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

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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

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

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


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?

 

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)

I'm really anxious to see what Theo comes up with when he swaps on the C4 setup

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!

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...