Nothing goes smoothly lately...

I installed a brand new MC, proportioning valve, dual 8" booster and rear Cadillac disc brakes from MP. On the front, I have new C4 Corvette 12" calipers, rotors and pads. The only thing I did not change is the brake lines and the distribution block bolted on the frame.

Everything is nice and tight, no leaks. The booster seems to be OK according to the MP troubleshooting site. I have 22" of vacuum at idle. Originaly, my car had power drum brakes all around.

My brake pedal is hard as a rock and the car barely stops. I drove it for a while but no measurable improvement. I cannot even lock the front brakes.

What is wrong???? HELP!!!
I am getting really frustrated with this.

Theo.
'68 Chevelle Conv. sb400.

First off, what is your MC bore diameter?

Second, your C4/Caddy setup might lead, down the road, to some problems. There needs to be a balance between the brake piston size front to rear.

Joe

when you open a bleeder screw on a caliper does the pedal go down fine?

My MC is 1 1/8" diameter disc/disc. I believe it is a Corvette one. I bought everything, except the front brakes, from MP. In addition, MP sells the same C4 Corvette front brakes as their 12" package.

The pedal goes down fine when a bleed screw is open. It does not bind in any way.

I keep calling MP but I always get an answering machine... That's great customer service!

Theo.

With that front caliper and vacuum assist a 15/16" master cylinder will be needed to generate enough line pressure.

The 1 1/8" MC is too big for vacuum assist systems with the PBR caliper.

The problem, as mentioned above, is that in order to generate enough line pressure to get the fronts to work correctly the rears may then have too much line pressure. Locking up the rear brakes prematurely gets ugly in a hurry.

CarlC,

I went with what MP Brakes is selling. They sold me the rear kit and they are selling the front corvette kit with the 1 1/8 MC. You can see it at: MP Brakes 12" Corvette (http://www.mpbrakes.com/db1780p.HTM). For rear brakes I have the following: MP Brakes Rear Disk Brake Kit (http://www.mpbrakes.com/reardisc.HTM)

Somehow, I think that something else is wrong somewhere. I hope that I'll be able to get hold of them soon...

Theo.

Sorry Theo, Carl C is correct. Just a few minutes ago I solved the same problem. I put Wilwood on all 4 corners Master Brakes distribtion block for 4 wheel discs, and all new lines, but it only slowed down. I then changed the master cylinder to a 1" from a 1 1/4". I just returned from the test run. I can stop now, but I think I will add an adjustable porportioning valve. Do you have braided steel instead of rubber going to the calipers? If not I think you will want them to keep a hard feeling peddle. Wish you the best with your brakes. Edd

Edd,

I will try this next week. I hope this will be the end of my problem... What master cylinder did you get? Do you have the part number or year/model of car?

Do you have a combination valve in your setup? I am not familiar about their operation. I understand that they sometimes get stuck to front or rear brakes, if you bleed both front or rear together... Does anyone have any experience or input on that?

Thanks,
Theo.

Originally posted by CarlC:
With that front caliper and vacuum assist a 15/16" master cylinder will be needed to generate enough line pressure.

The 1 1/8" MC is way to big for vacuum assist systems with the PBR caliper. Exactly. You'll probably want a 15/16" bore MC to use with the PBR's.

A good MC to use for this app is for a 77 Malibu 6 Cylinder with MANUAL brakes. It is a 15/16" bore MC. The only caveat is that on that particular MC the front port goes to the rear brakes, and the rear port is for the front brakes, so you will have to re-do your plumbing a bit. I use this particular MC in my app (PBR's all around) and it works well with my Hydroboost. It should also work well with a vacuum booster.

Troy

Theo, I cannot find the numbers on the master cylinder. The purpose of a combination valve is to give correct bias on the front and rear brakes,it slows down and cuts the amount of pressure to the back brakes. To tell if your valve is tripped, take your test light to a positive and touch the top of the switch,if it lights its tripped,if not its ok. If its tripped go to the side with the flow open a bleeder and slowly depress the pedal until the light goes out. Close the bleeder, its reset. Hope this helps but I'll bet you a coke if you ask them about the master cylinder they will give you the right one. Edd

The problem is that there are companies that sell brake kits and there are companies that sell brake systems. It is almost scarry how easy it is to buy a "kit" that is several steps down in performance than the factory designed "system."

Unfortunately, except for one, maybe two, company(s) actually sell a brake system, something that is engineered to work together. All the others are selling kits that have a lot of "WOW" and not a lot, if any, engineering.

Let's look at this problem from a practical standpoint.

Ford uses the PBR caliper in millions of Mustangs. They use, from the best measurements that I can take without disassembling the MC, a 1" bore MC. It might be smaller but without gutting it I cannot tell. There is no way it is larger than 1". This system is factory engineered to work correctly using a hydraboost assist unit which makes significantly more assist than any vacuum setup.

The 1992-6 Camaro Z28 and the C4 Vette use the same caliper with a similarly sized MC.

Now let's start our own brake company and realize that the most obtainable (read CHEAPEST) GM master cylinder on the planet is the 1 1/8" passenger car type. This MC is designed to be used with a single piston caliper with a big-ass piston area. Hence, low line pressures, high pedal, great reliability.

If a 1 1/8" MC is used with a PBR caliper a 27% increase in pedal effort is required to get the same line pressure as a 1" MC. 45% if a 15/16" is used. Throw in a smaller diameter booster and it gets much worse.

"We've sold hundreds of these kits and never hear of any problems." Yeah, right.

"We have 1" master cylinders for $100." Why wasn't it supplied with the kit?

I had the president of one of the BIG companies tell me several times that I had a volume problem with a 1 1/8" MC, not pressure. Funny, as soon as I changed to the smaller MC, the line pressure problem went away.

Here's a test that I ran during my hydraboost swap. Before the swap, using a 1" MC, factory large diameter booster, engine revved up and making vacuum, the best line pressure I could get was around 900 psi and did not stop well. With the HB 1500 psi is possible. Now the car stops the way it should.

It may be copy-catting, but studying the factory installed SYSTEMS is by far the best way to determine braking balance and proportioning. Mixing and matching of components can be expensive and dangerous without a through understanding of all their interactions.

Thanks guys!

Troy, I will check out the 77 Malibu MC. MP Brakes has a Manual MC for disc/disc systems that is exactly the same as the power one, except it has 1" bore. They are asking $119 for it!!! I hope they tell me which car it comes from because the local autoparts store does not know how to find the part... Does anyone know what car it came from?

It is the MC390360M master cylinder shown in: MP Master Cylinders (http://www.911brakes.com/mcdimensions1pdf.htm)


I will also see what MP Brakes will tell me on Monday.

This really sucks because MP is selling the 12" Corvette caliper kit with 1 1/8" master cylinder... As an engineer, it upsets me when companies sell things without testing them first.

Theo.

Theo,

Your local NAPA can look up MC's by bore size. It takes some manual catalog hunting but it can be done.

Be sure to get one that has the same depth actuator rod hole depth on the piston. Most manual setups have a deep hole while the power types have a shallow hole.

I have a 1" that came from a disk-disk late 2nd gen Trans Am. Something like a 1980 or so. I would highly suggest based on my experience with this part to find either a 15/16" or 7/8" MC. It won't be easy since 99.9999% of power MC's to fit the Delco power booster won't have a piston that small.

If you want to use a later model MC and have access to a lathe you can do the modification done here http://www.geocities.com/torkerscamaro/torker.html
I did the machine work on the MC register. It's easy. Just be sure that before you buy the MC that there is going to be enough meat left in the register wall to fit inside of the vacuum booster. This setup should work very well for you.

I'm an engineer as well and made the assumption that the aftermarket brake companies do their homework. Unfortunately most of them are just butchers.

One place that makes pretty good parts that is in your area is American Brakes and Steering. They did the HB unit in the website above. They may be able to set you up with a MC.

CarlC,

I also did a search for 15/16" MC and I came up with the "torker" website. I am glad that you are suggesting the same site.

I just got off the phone with the local autoparts store and I ordered a new 1988 S10 manual brake 15/16" MC with reservoir for $60. If the fittings are the same, it should plug in, after I reduce the register diameter. Since I do not have access to a lathe, can I sand it down to make it fit?

Thanks again,
Theo.

It would be really hard to sand/grind the OD.

What you need to find is a little hole-in-the-wall machine shop with an old salt that will give you a good deal. If you have a hard time finding one let me know and I'll see what I can do.

Just be sure to measure the booster bore vs. OD of the MC register to confirm wall thickness.

Another source for MC is http://www.rockauto.com I think Torker paid something like $35 including core charge.

CarlC,

I just picked up the MC I ordered and it is 1 1/4" bore... Apparently there are two sizes for manual brakes and the autoparts stores do not differentiate in their database.

I'll have to do some more searching to find the 15/16" (24mm) bore Cardone part number. I believe the Wagner part # is R105801. Is there any difference between the 24mm manual and power master cylinders (both same diameter bore)?

You are right about reducing the OD. I'll find a machine shop for that.

Theo.

Take a look at my website to find the #'s on a 15/16" bore MC and how to adapt the late model aluminum MC's to our cars. graemlins/thumbsup.gif

Joe

Joe,

Did you use the *Manual* brake S10 MC? There are two 24mm MC's for the S10.

With Power Brakes: 24 & 36mm cylinder bore
W/out Power Brakes: 24 & 31.75 cylinder bore

I assume that the larger bore value is for the rear cylinders? The port to the front of the car is for front brakes and the rear for the rear? Correct?

Thanks,
Theo.

If I'm not mistaken the S-10 MC's are "quick take up" style; they use a larger bore to move the fluid in less pedal stroke to get the pads into contact, then switch over and use the smaller bore for actually delivering the line pressure.

Troy

Hey Guys,

I was just reading through this thread. I am using the S10 MC on my GTO. I have the front brakes hooked up to the rear port and the rear brakes to the front port. I am using rather large Wilwood calipers on the front, so I need extra fluid (quick take up feature) going to the front. This works very well on my car. Its a manual setup.

Andrew

The S10 master cylinder is the quick take-up kind. I just bought a manual one, finally. Tomorrow, I will reduce the OD, on the booster side, to make it fit my dual 8" booster.

I have the C4 (dual piston) calipers on the front and Cadillac (single piston) calipers on the back. I plan to connect the front port (toward front of car) to the front brakes and the rear to the rears. I hope that's going to be fine. I can't wait! I really can't believe that companies like MP Brakes are using 1 1/8" MC (same as the one I had) with the Corvette brake setup... I am sure they have a lot of calls, if they sell any.

Theo.

Theo,
Sorry I couldn’t answer you question quick enough. The MC is the manual brake one. The front brakes (C5/LS1 style) are connected to the rear port and rear brakes (LT1/C4 style) are connected to the front. I do believe in discussions with Troy about his ’89 TTA, it is plumbed that way from the factory.

The quick take-up MC’s have three pistons inside the bore. Your C4 style front PBR calipers are of the quick take-up caliper variety. As I state on my website, the engineers use this style of MC to help out with gas mileage primarily by having the third piston suck back the fluid & thus the caliper piston to help out with caliper drag that is normal in disc brake systems. The third piston will quickly push back the piston(s) when the brake pedal is applied.

Ever wonder why the NHRA super stock class racers generally run drum brakes up front? Its so they can adjust the brakes for no drag.

I would warn you about the caddy/TA rear disc setup you have as I stated previously. The piston area verses the piston area of the front C4 PBR’s is not what you want to see for a four-wheel disc brake system. The caddy/TA caliper does lose some of its effective pressure area due to the internal parking brake power screw, but I don’t believe its enough to bring the system into balance. With such a huge piston area in the rear and your tires unloading in the rear when panic stopped, you are likely to have the rear end and front end want to swap each other. Not fun at all with your prized possesion! Most people think they can just turn down the pressure with the adjustable proportioning valve, but it might not be enough in some situations. I would suggest changing out to the C4/LT1 rear PBR’s for your swap. I know it’s not what you want to hear, but it may save you and your prized ride (not to mention you’ll need to change your shorts) a trip somewhere that will really hurt your wallet ($$$). Sell the system to guys doing the Suburban caliper swap or have stock discs up front to regain some of your dough.

Good luck with what you decide on.

Joe

Joe,

It seems that I opened a can of worms... I probably should have never gone with the C4 front brakes as I would be done now.

I will try using the Cadillac rear brakes and see how they work. I will change them if they tend to lock.

So, with my brakes (C4 front, Cadillac rear), would you still connect the rear brakes to the front port? Is there a difference between the ports? What is the logic there?

Thank you for your help,
Theo.

Originally posted by Theo:
Joe,

It seems that I opened a can of worms...
Theo. No you haven't opened a can of worms. I just wanted to let you know what could happen in a higher speed panic situation.

If I were you I would still connect the front port to the rear and the rear port to the front. Just because the PBR's quick take up caliper design.

You'll be fine for stop and go traffic, but just be aware what could happen with "spirited" driving/braking.

You might want to read David Pozzi's write up on the quick take-up MC.

Click here (http://ourworld.compuserve.com/homepages/David_Pozzi/quick_take_up_master_cyl.htm#Quick%20Take%20Up%20M aster%20Cylinder%20for%20Manual%20Brakes)

Joe

Thanks Joe.

I primed the S10 Manual brake MC and installed/connected it as you suggested. A friend of mine is helping me bleed the system tomorrow morning.

I am using a proportioning valve, which, I hope, will make the whole system balance out... As a ex-racer, brakes are extremely important to me, even more than hp. I hope all will be just fine.

Theo.

Theo-I haven't expeirened this with aftermarket stuff however at the Chrysler i work at we get our share of mini vans that have the same exact symptoms after doing a front brake job. Seems when you stroke the pedal to the floor to "pump the brakes up" it ruins the diaphrame in the booster and the booster is now in-op. try running the car with the booster unplugged from vaccum and see if the pedal "feel" changes. if not you may have a bad booster.

Dennis,

I did the booster test that MP Brakes has in their website and the booster is OK, according to that. I will be more positive about that after I bleed the brakes with the new 15/16" S10 manual MC, in a couple of hours...

Thanks,
Theo.

Well, I am completely lost now. I bled the brakes twice. First manually (waited 15secs after each pump), and then with a vacuum bleeder.

I cannot even lock the front brakes. The pedal goes all the way to the floor and the car barely stops. When the engine is off, the brake pedal is hard and moves only about 1" from top.

I have no leaks. The front and rear calipers, rotors & pads are new. I am using the correct manual brake S10 master cylinder (which, I bench bled), a combination valve (tested OK), and a dual 8" booster. The booster passes the MP Brakes test. I wired the rear brakes (1/4" lines) to the front MC outlet.

What can be wrong?

I should be able to lock the front brakes regardless of the rear brakes, right?

Should I have the system pressure bled? Any ideas?

Thanks everyone and Happy Turkey day!!!

Theo.

Lets see Theo...

Look for the obvious first when trying to figure this out.

Do you happen to have access to a digital camera to take pics of the setup?

Is this the dual diaphram booster you are using? What kind of vacuum are you pulling with your motor? They take a lot of vacuum to operate.

The rear caddy calipers probably aren't adjusted out correctly (they're notorious for it).

Was the car originally a power booster equipped car?

Are the bleeders pointed towards the top?

Look for the obvious first before you start throwing your time, effort and $$$ into this.

Joe

Joe,

I have a dual 8" booster. My vacuum at idle is 22"+ (stock small block 400). I followed the instructions to adjust the rear calipers. I even believe they were too tight. I will check them again but, should they affect the front brakes that much? I cannot lock the front brakes at all. The pedal goes all the way to the floor, when the car is running. I have a hard pedal, when the car is OFF.

The car originaly had power drum brakes all around. There is a distribution block bolted on the frame. MP Brakes told me that it is just a junction block, but the brake light goes ON when I press on the brake pedal too far. The is an electrical connection on the block.

I also have the MP brakes disc/disc combination valve under the MC, which is operating correctly (no brake light ON, when I test it).

All the bleeder screws are on top. I ordered a pressure bleeder adapter for the MC. I want to cover all areas...

I do have a digital camera and I can take any picture you want. Just let me know.

I appreciate your help,

Theo.

I'm confused how you have the disk/disk block and the origional drum block both plumbed into the system at the same time? The disk/disk block should have 2 front outlets and a rear outlet and you shouldn't need the origional block.

Peter

Peter,

I asked MP Brakes about the same thing and they said that the original drum/drum block is just a junction box. They said that I do not need to remove it...

I am getting the "Brake" light ON, from the drum/drum block, when the pedal goes all the way to the floor. So, I am not sure what is going on. There must be some kind of valve in there.

What have other people done? Do they remove it or leave it?

Theo.

Originally posted by Theo:

I am getting the "Brake" light ON, from the drum/drum block, when the pedal goes all the way to the floor. So, I am not sure what is going on. There must be some kind of valve in there.
The only thing in the drum/drum block is a safety switch (what trips the light). This occurs when the block sees a pressure differential across both inlet ports. You cannot have any sort of proportioning valve before the distribution block; otherwise there will be a pressure differential between the front and rear circuits and the switch will trip, which not only turns the light on but also cuts the fluid flow to the circuit with the low pressure.

I had this same problem when I installed my adjustable proportioning valve between the master cylinder and my drum/drum distribution block; I'd get hard on the brakes and the warning light would come on. I knew better than to install the proportioning valve there, but I did it anyways. graemlins/clonk.gif

I have since relocated the proportioning valve to the front to rear brake line along the frame AFTER the distribution block and I have no more problems.

What you'll need to do is eliminate the drum/drum block on the frame and only run the MP brakes combination valve.

Troy

I'm confused now Theo. Are you running a brass combo valve before the drum junction block and not a knob style adjustable proportioning valve?

If you are, get rid of the drum junction block and just run the MP brass brake combo valve in its location. More than likely you'll need some brake line adaptor fittings to allow everything to bolt up.

A pic of your MC & how you have everything plumbed up (combintation block and drum junction block) would be nice.

Joe

Troy & Joe,

I think that you are right. I will eliminate the drum/drum junction box on the frame. It upsets me that MP Brakes has been wrong in everything they told me.

I took some pictures of my connections:

This one shows the MC and the MP Brakes disc/disc combination valve:
Picture 1 (http://mysite.verizon.net/res0cslo/IMG_0680.JPG)

This one shows (hard to see) the drum/drum valve on the frame:
Picture 2 (http://mysite.verizon.net/res0cslo/IMG_0681.JPG)

This one shows a spare drum/drum valve that I bought so that I figure out what it does... The center opening is for the "BRAKE" light. I can see a spring in it. How can I take it further apart?
Picture 3 (http://mysite.verizon.net/res0cslo/IMG_0682.JPG)

Theo

Theo,
Any chance you could get a picture from the other side of the MP valve in picture 1??

Also, the reservoir you are currently using probably is going to hurt you down the road for the amount of fluid volume it can hold. Grab one off a third gen f-body or '91+ B-body as these were designed for angled MC setups. graemlins/thumbsup.gif She'll swap right on.

Joe

Theo,

I suspect that the MP valve under MC is the cause of you problems. That S10 MC should generate some really good pressure when combined with a booster. It works great in my car in a manual application. The only pressure reducing device should be the adjustable prop valve, plumbed into the rear line.

Another thing to check is to see if you have a pressure reducing valve in the rear line. Look on the front side of the rear cross member. See if there is a little valve just to the left of where the hard line mates to the flex line going to the rear end housing.

Andrew

The only thing I could think of is that you have the line coming out the front (as it's mounted) of the proportioning valve under the master going to the front brake line. Otherwise, maybe it's still a bleeding prblem. Try waiting for more time when bleeding.

Are you using DOT 5 brake fluid? That stuff is really hard to bleed because it's easy to aerate so it's full of bubbles. You have to go extremely slow with it.

What did you do with the other hole in that new valve? The one on the back towards the booster. That's where the other front brake line usually goes.

You can mount the new valve down at the frame in place of the other one. I think you need to adapt the size of the rear line but other than that it should bolt on. Then, you run the lines to the master like it was stock.

The stock block has a valve in the middle. It's basically a solid round piece with a V cut into the middle. If the pressure front to back isn't the same it's pushed off centre and the switch that is opened by dropping into the V get closed. There's the same type of thing in the other block measuring the pressures before the rear brake pressur gets reduced.

I have to agree with Joe in that the front and rear brakes are mismatched and could lead to rear lockup. The thing about that is you won't know until you're cruising at a good clip and have to brake hard when it will be too late. Do some decent panic stop testing when you get things working.

Peter

Any further news Theo?

Andrew

I just came back from a business trip... I am trying to catch up with all your great suggestions. Thank you all, again.

What I plan to do is remove the original drum/drum prop valve that is installed on the frame and leave only the MP valve. I should do it in the next couple of days.

I will swap the MC reservoir, as per Joe's suggestion. Joe, I can take a picture of the MP Valve other side but there is nothing there, except a plugged front brake outlet. The MP people said that I can use either one or both. Is there something else I should know???

After I remove the stock valve, I'll see if the front or rear locks first during panic braking. If it is the rear, I will either replace them with the Corvette brakes or install a rear adjustable prop valve. What do you guys think? Will I be opening another can of worms???

If I cannot lock the brakes (after I remove the stock valve), I will also remove the MP valve and use a rear only adjustable prop valve, as per Andrew's, suggestion.

Peter, the line that's coming out of the front of the prop valve (front of the car) goes to the rear brakes. I will remove the stock drum/drum prop valve at the frame and see what happens. I will definitely do a lot of panic stop testing before I finalize things.

This started as a brake improvement project but it became the never ending project...

Theo.

Joe,

The local Chevy dealer parts people are kind of jerks... They can only order the whole MC and I just need the reservoir. Can you tell me what years & models are the third gen f-body or '91+ B-body cars? This way I can get a remanufactured MC from an autoparts store, with actually helpful people...

I made some progress today... I removed the stock drum/drum valve & lines and I bought new brake lines and connectors. I expect to do the work tomorrow. I am keeping my fingers crossed.

Theo.

Theo,
A junkyard might be a better shot than the GM dealer for the reservoir.

I do believe all third gen f-bodies '82-'92 had the right one and '91+ Caprices (could be used earlier...I haven't snooped around enough to check that out) should also have the angled reservoir.

If you can't find one let me know and I'll see if I can grab one for you.

Joe

CarlC,

Questions about my '67 camaro's "pdqCBB" setup..

I finally got over here and have to ask if I will have a problem with my big single piston Van front calipers and 1980 Seville rear calipers balance-wise?

The Van calipers are 2-15/16" dia. and the Seville calipers are right at 2.00" dia.

I have installed my prop. valve on the M/C port closet the firewall which should be the rear brakes then to my stock four wheel drum brake block under the M/C. This is correct isn't it.

AND since I am hard-headed, I am going to try a 1.25" M/C and will have to can it if it doesn't work!! Per david Pozzi's thought's too..

Please advise. Awaiting your and anybody else's comments..

Thanks in advance.

pdq67

PS., the big calipers and 13" Vette rotors on the front look like they are stock!!!

I finally run all the hard lines needed when I removed the stock drum/drum combination valve. Now I have a 1/4" line for the rear brakes and two separate 3/16" lines for the front brakes. The front MC outlet feeds the rear brakes. There are no leaks that I can see. I also got a camaro reservoir, which is perfect! Thank you guys! Joe, thank you for the offer. I appreciate it. Do you need a new remanufactured Camaro MC without the the reservoir?

I vacuum bled the system. I am not sure if this is a good way for this MC and calipers but I had no helper available. My wife will not come close to the garage... The pedal is hard and moves about 1" with the engine OFF. With the engine ON, the pedal moves almost all the way to the floor. Again, I cannot lock the front or rear wheels no matter how hard I try. The pedal feels spongy. It stops a little better than before though.

I am not sure if there is more air in the system. If there isn't, I may have to eliminate the MP Brakes disc/disc Combination valve Combination Valve Info (http://www.mpbrakes.com/mp21.htm) and install just a proportioning valve Prop. Valve Info (http://www.mpbrakes.com/vl3350w.htm) on the rear circuit. I ordered a brake pressure bleeder adaptor for my compressor so that I bleed the brakes again.

This is the MP Brakes troubleshooting for spongy pedal: Spongy Pedal Reasons (http://www.mpbrakes.com/trouble1.htm). It may be that the MC is too small diameter for the rear brakes...

What do you guys think?

Theo.

Originally posted by Theo:
Do you need a new remanufactured Camaro MC without the reservoir? What size bore is it?


Originally posted by Theo:
It may be that the MC is too small diameter for the rear brakes... True, the MC might not have enough pump stroke to move enough fluid volume to fill the huge pistons that are in the rear disc calipers.

What I would do is make sure the combo valve from MP is plumbed right. That other front brake port is used on the valve also and not capped off like it was when you got the valve.

If that doesn’t work I would use the stock junction block with a knob style adjustable proportioning valve in the rear brake line.

Bleed the system again. Follow David Pozzi’s recommendations when bleeding the MC. Tell the wife she has to help ;)


Let us know how things are going. And don’t forget the beer when this is all done!

Joe

Joe,

I did another test. I pinched the rear brake lines, right before the calipers, and the pedal was hard with the engine OFF. So, the rear calipers have something to do with the spongy pedal.

In addition, the car hardly stops with the pinched rear brake lines. Shouldn't the front brakes still stop the car? Is this a by-product of the combination valve or something else is wrong?

The pinched brake line test confirmed to me that my MC is OK. It seems that it might be undersized for the rear Cadillac calipers.

My connections are like this:
The forward MC port is connected to the rear brake IN of the Combination valve. The front brakes are connected to the two front OUT of the Combination valve. So, I used all the Combination valve ports.


Now, I am on a search for Corvette C4 rear calipers and rotors. Does anyone know if the 1st gen. Camaro axle housing flange is the same as the '68 Chevelle? I think they should be...

I feel that I am getting closer, slowly...

Regarding the reman. Camaro MC, I believe it is 15/16" bore. The Cardone # is 10-2057. If you can use it, it's yours.

Theo.

Originally posted by Theo:
Joe,

So, the rear calipers have something to do with the spongy pedal.

The pinched brake line test confirmed to me that my MC is OK. It seems that it might be undersized for the rear Cadillac calipers.I think you are right. There just doesn't seem to be enough fluid volume being pushed back to your rear calipers. But I would recommend before you start swapping out expensive parts to bleed this MC following David Pozzi's recommendations though to see what happens.

From David Pozzi’s website
This Master cyl can take a lot of time to bleed the rear brakes on, due to the small refill port from reservoir to rear bore. You must take at least thirty seconds or more before applying the brakes for each stroke when bleeding, to allow time for the rear bore to refill.
Originally posted by Theo:

Now, I am on a search for Corvette C4 rear calipers and rotors. Does anyone know if the 1st gen. Camaro axle housing flange is the same as the '68 Chevelle? I think they should be...
Yes, they are the same. The LT1 setup bolts up with the calipers facing the back of the car on LT1 F-bodies (if I can remember correctly). You’ll want to swap the LH side setup onto the RH side of your Chevelle and vice versa for the other side to avoid interference with shocks and their studs.


Originally posted by Theo:

Regarding the reman. Camaro MC, I believe it is 15/16" bore. The Cardone # is 10-2057. If you can use it, it's yours.

Theo. Yeah, I can always use it and if not I can chuck it up on a lathe to turn down the O.D. for someone else to use on the early style Moraine booster for this kind of swap.

e-mail me: Joseph.Whiles@harley-davidson.com

Let me know how your bleeding goes and what you decide to do.

Joe

Theo,

I'll bet there's still some air in the system. I too used both a vacuum pump and pressurized setup but still could not get all of the air out. 20 minutes using Torker's leg and the pedal firmed up nicely.

Once you know for sure (and that's not easy) that the air is out you may want to pinch the front lines to find out if there is enough MC volume to fully actuate the rear caliper. Don't pinch the front lines if they are braided steel. Teflon does not like to be squished.

I don't know about the interchangabilty of early Camaro and your car but if the backing plates are the same, or have the same bolt pattern, you may very well be able to use the 93-96 Z-28 rear setup. Torker's website has some good pictures and some measurements that may be helpful. Looks like Joe's got the lowdown as well.

pdq,

I'll have to re-find the piston sizes for 3-4 OEM setups and start comparing.

I'd bet on air too. Even if the master can't provide the fluid for the rear brakes it should still operate the fronts.

What type of fluid are you using?

Peter

I really hope that you guys are right.

The way I see it, the rear calipers do not retract as much as the front ones, as they are not the quick take take-up (?) type. So, the rears should (hopefully) require almost equivalent fluid requirements as the fronts. The MC is designed to handle this situation.

I am using the Valvoline Synthetic brake fluid. That's the best I can find locally.

I just received the pressure bleeded and I plan to bleed the system again today. I hope I see a difference. I also plan to recruit my wife... It has to be good exercise for her legs...

Theo.

I pressure bled the whole system twice and used 2 quarts of new brake fluid. No change in brake pedal. It is still soft and goes all the way to the floor when the engine is ON. I still cannot lock the front brakes.

What the hell???? What else can be wrong???

Here is a summary of my system:
Front - Double Piston Corvette C4 12" calipers
Rear - Single piston Cadillac 11" calipers
Booster - MP Brakes Dual 8". It seems to work.
MC - S10 15/16" manual brake. The front outlet (front of the car) is connected to the rear brakes with 1/4" line.
Combination Valve - MP Brake disc/disc combination valve. Rear Brakes connected with single 1/4" line. Front brakes use their one outlet from the comb. valve with 3/16" lines.
Here is a picture: MC & Combination Valve (http://mysite.verizon.net/res0cslo/IMG_0680.JPG).

Is it the combination valve or the rear calipers?
When I clamp the rear caliper lines, the pedal is hard but the car barely stops.

Theo

I'm a little confused about the pedal. When you clamp the rear lines you have good pedal with the engine running but the car still won't stop? You should be able to drive with front brakes only and have fairly decent stopping power.

The synthetic fluid could be the problem. The DOT5 stuff is a major major pain to bleed. I had to drill the port from the reservoir to the cylinder in the master to get it to work for me. It tends to get saturated with small air bubbles when you work with it that are hard to get out.

How are you pressurizing the plastic reservoir? IF you are, try putting the vacuum pump on it for a while, or just hook a vacuum line from there to an engine vacuum port and leave the car idling for a bit and operate the brakes at the same time. Maybe that will suck some of the air out of the fluid?

The only other thing I can think of is that the operating (push) rod in the booster is the wrong length and it's either not pushing the pistons in enough or it's not letting the piston all the way back in the bore.

Peter

How we doing guy's??

pdq67

Peter,

I used the pressure bleeder system that pushes fluid directly in the fluid inlets with two metal tubes (it is made KD tools). It is kind of hard to describe... I used it with a Garden sprayer for pressure. It works well. I've used a similar setup for my race car for a long time. I used to flash the brake fluid every couple of races.

The fluid I am using is DOT 3 & DOT 4 compatible Valvoline synthetic. It is not DOT 5, which is silicon based. So, the fluid should be OK.

From what I could tell the S10 MC is the same type (short piston depth?) as the 1 1/8" Corvette MC I originally bought from MP Brakes. The Booster is made for this kind of MC. Also, I adjusted the brake pedal to not push the MC at rest. It has a little play.

Regarding what happened when I clamped the rear brakes, I am also confused. I attibute the result to the Combination valve. I am not that familiar with is function. The only thing I know is that it is connected correctly and that it is not locked in one position (Brake warning sensor is OK). Any ideas/opinions on that?

So... now, I am down to the fact that the piston size of the rear calipers might be too large for the 15/16" MC. I really thought that the "quick take-up" MC would compensate for that, but who knows. I am pretty sure I adjusted the Cadillac calipers correctly. I will try again though.

I ordered a set of C4 rear calipers and brackets. I should receive them by the end of this week. I hope that next week I'll be on the road again...

Theo.

Theo,
I think in the end of this we are going to find out the piston areas when compared to front to back is just not going to work with the size MC that the C4 calipers need to generate any amount of line pressure necessary to brake with them.

There is just a trade off with MC bores.

When the MC bore is big the stroke required to generate volume isn't as much as if the bore was small, but you generate more line pressure to operate those tiny caliper pistons.

Pressure = Force/Area

To get a little you have to give a little away. Its a catch-22 with this kind of work.

I'm thinking with a step bore MC we could make the swap work in your case, but I've yet to come across such a monster that would work with our cars :( Anyone out there know of an application that offers step bores?

Joe

Joe,

So what are you saying? Will the 15/16" MC work with the front and rear C4 brakes? Is the quick take-up kind MC a step bore?

I just received the rear Camaro/Firebird (C4 BPR) calipers with parking brake assemblies. I am waiting on the mounting bracket and rotors. I should have them by middle next week.

Since I was planning on installing a posi diff and I will need to remove the rear axles to install the rear caliper mounting brackets, I will have the diff people install the brackets at the diff swap. If everything will fit, I should be set... I hope.

Theo.

Originally posted by Theo:
Joe,

So what are you saying? Will the 15/16" MC work with the front and rear C4 brakes? Is the quick take-up kind MC a step bore?

Theo. Yes, the MC you have right now will work wonderfully with the C4 front and rear setup.

Have you decided to sell the Caddy setup to guys running stock discs up front?

Joe

Once again Ih ave been following closely. I have a theory.

It seems that your problem is a lack of volume that is being sent to the rear calipers. The "quick takeup" (read more volume) function on the S10 MC was originally developed for this exact same problem that you are experiencing. The S10 pickups used large bore cylinders in the rear drums, so they needed the extra volume. However the "quick takeup" function is only on the REAR port of the MC. This is the reason I have my front brakes plumbed to the rear port. My front calipers have 6 pistons and require the extra volume. In your setup, you need the extra volume for the rear.
Have you tried plumbing the rear brakes to the rear port? Did you ever check if you have a factory prop valve on the rear crossmember?

Andrew

Andrew,
Good theory, but I just think the Caddy calipers require way too much volume for this MC to cope with. With the small bore the stroke required to push the necessary amount of volume to the caddy calipers makes you bottom out on the MC before the volume is reached.

That and the fact that the front calipers should be 40-50% larger than the rears or something that I talked about on the first page of this thread could happen.

What do you think?

I've also read some articles, that I could get my hands on, about the quick take up MC is that they were used in conjunction with front calipers that came with specially cut piston seals that allowed less drag when fluid volume was retracted back.

I could be wrong though as all those BB_Mike years of drinking beer in college do catch up with you later in life :D

I'm willing to bet that once Theo bolts up the C4/LT1 rear calipers & discs that he'll have a grin on his face from ear to ear graemlins/thumbsup.gif

Anyone else out there have any ideas?

Joe

Well, the proportioning block has a valve/switch that measure differences in pressure so if the front was making pressure and the rear wasn't the switch should be closing and putting the brake light on. Since that master should work fine with the front calipers but everyone thinks there isn't enough fluid volume for the rears then this is what should be happening. But, the light isn't going on. Because of this, I'm not totally convinced that the fluid volume is the problem.

I thought the PBR calipers required a quick take-up master because they were low drag. Doesn't this mean that both ports of the master need to be quick take up to match the calipers?

I agree with Andrew, if the quick take up port of the master is the rear one then the rear brakes should be connected to it.

Peter

Here is some more info on the S10 quick take up MC. I should mention that it took me FOREVER to bleed my system. So make sure that there is no air in your system.

http://www.babcox.com/editorial/bf/bf60133.htm

Quick take up info (http://ourworld.compuserve.com/homepages/David_Pozzi/quick_take_up_master_cyl.htm#Quick%20Take%20Up%20M aster%20Cylinder%20for%20Manual%20Brakes)


Incidently, I am using the C4 12 inch rotor setup in the rear of my GTO. They seem to be perfectly balanced with my Wilwood 6 piston calipers in the front.

Andrew

Happy Holidays everyone!

I've been collecting parts all this time... This is what I am planning to do.

On the front, I will be installing the 13" HD C4 Brakes (J55). I got a good deal on the setup.
On the rear, I will install the 1993-97 12" PBR Camaro/Firebird calipers with built-in handbrake. They are the same as the C4 calipers.
I will keep the S10 MC and the MP Brakes combination valve, connected the way it is now. If the comb. valve creates problems, I will replace it with an adjustable valve, on the rear circuit only.
I will also install braided lines all around.

I will do all this on the first week of next year, when I'll replace my diff. The rear caliper brackets require removal of the rear axles, so I figured that's a great time to do it.

Joe, I will sell my Cadillac rear setup. Let me know if you are interested.

I'll keep you posted about my progress.
Theo.

Theo,
Thanks for the offer. I've got the LS1/C5 rear disc swap going on right now.

Though, I'm sure someone on this board will want them. Have you tried placing an ad in the TC classifieds?

graemlins/beers.gif

Theo,

Did you ever check to see if you have a little factory valve in the rear line, on the rear crossmember?

Andrew

Originally posted by andrewb70:
Theo,

Did you ever check to see if you have a little factory valve in the rear line, on the rear crossmember?

Andrew Andrew,
Are you talking about the residual pressure valve back there? I've only seen those on Pontiacs (for some reason) :confused:

I'm really anxious to see what Theo comes up with when he swaps on the C4 setup graemlins/thumbsup.gif

Joe

Here is the latest update.

Because I switched to the 13" front brakes, I am ordering a new set of brake lines (longer). So, I am waiting on that for the moment. The 13" brakes look great with the 17" American Racing Torque II wheels! I cannot wait!

Another thing that you should know is that the C4 Corvette brake lines are the BUBBLE type, not the double flare. So, you will need to find the correct brake lines. I am ordering braided lines. What the hell... Since I am going all the way.

When I receive them, I will bleed the brakes and then take the car to the differential place to install the new diff and rear brake brackets (the axles need to be removed).

It is getting closer. I will keep you posted.

Theo.

Keep us updated Theo! graemlins/thumbsup.gif

Joe

Theo did you ever get your original problem solved of the hard brake pedal and car not stopping? i am way to lazy to read 5 pages of threads, sorry. the reason i ask is i put new brakes on my 67, wilwoods all 4 corners and a new master and prop. valve in rear. i had same problem. my fix was as simply as moving the rod that goes through the firewall from the pedal to the master. there are a couple holes on the pedal the just moving the rod(i cant remember up or down, wilwood site does into this, though) made all the difference in the world. if original problem fixxed sorry about the post, if not you might want to look at.

Any update Theo???

Joe

I'm curious how this story ends...