Ive posted before about the drum to disc swap that i did, and how things werent going so swell... So, being my daily driver, i had to put the drums back on (this is just a front disc conversion, backs remain drums). Now i have the time, and just bought brand new rotors, and am ready to go for it again.

I need to know if i am missing anything for the swap... I have the spindles with rotors and calipers and brake lines all assembled (so they are ready to be bolted on). I have that covered, but I have no booster (is that required?) and proportioning valves? and whatever else?? Shouldnt i be able to hook it right up to the brake lines, bleed them, and be ready?

Last time i did this, it took one full pump on the brake pedal before i would have pressure...and then i would slow down just fine. i bled them seveal times thinking i still had air in the lines.. but no change. Thats when i had to give up and put the drums back on (ouch!).

Any info would be great.

Thanks,

Bubba graemlins/clonk.gif some pictures of my 68 chevelle (http://www.garsworld.com/chev/default.htm)

Just a quick question? why are you goin back to drums??? if its your daily driver, wouldnt u want the better stopping power of the discs. I love mine, i did a four corner kit from SSBC with 2piston front single piston rear calipers. New brake lines from year one and master cyl. and brake booster from SSBC.

I only put the drums back on becasue the discs werent working right and i couldnt drive it with the non working discs. So i had to suffer and put the drums back on for the meantime... but believe me, i HATE the drums and have been anxiously waiting for time to go for the swap again. Someone was saying they werent bled right and that is why they werent working, if thats the case ill just get the car down to a brake shop and have them bleed them with their equipment. But i am posting now to see if i should swap the discs back on, get alignment, and bleed brakes. Should i go for it? I dont 'need' a booster, right? or proportioning valve? I should be set to just pu on the spindles, hook up brake lines, and bleed them corectly right?

Thanks

Bubba

Hey Bubba,
You have got to change out the proportioning valve and the master cylinder. I do not know if the booster maters as there are non power disc cars out there. If its a drum/drum setup these need to be changed to a disc/drum unit. Maybe thats what happened to you the last time. I bought a MP brakes master cylinder and combo valve kit, still need to install it.
Anyone else? Corrections?

John C.
65 wagon project.

What is the difference between the new master that i need and the one i currently have (it is pretty big with 2 resevoirs if that explains it). The brake lines go down to a square block on the frame (is that the proportioning valve?)

A guy who restores chevelles tells me it should work with what i have...

Bubba

A brake booster is recomended for these applications, especially if u are making some decent power with your engine. Remember, no matter how fast your car can go, its useless if u cant stop!! As for a proportioning valve, a new one came in my kit and works great, although you really only use it once. Once you get good proportion between front and rear, you can pretty much leave it as it is.

Anyone, please correct me if I am wrong, but.....

Disc brakes need far more pressure to operate than a drum master cylinder can provide.
Hence why there are drum/drum, disc/drum, and disc/disc master cylinders.

Your setup was lacking the needed presure to clamp down on the rotors. It was not to long ago that one of the hot-rod magazines went over this info. I never really understood it until that article was published. It takes more pressure to clamp down on the rotor that to push out the drum shoes.
Check with MP brakes, they have a great tech help system. But I reallythink this "guy who restores Chevelles" may be off target.
John C.

that's correct, disc need more pressure

you HAVE to buy a new master cylinder, it's less than $20! Mine was $14

you NEED to have a proportioning valve, on a 69 i think its like a 70 and there is one by themaster cylinder and one near the rear axle

the one near the rear axle is there to make sure the rear brakes lock before the front, without it the front locks before the rear even start to work (good for burnouts but causes nose dives :D )

I would recommend a brake booster too, you'll be much happier with power brakes.

Also a good set of brake pads are another cheap improvement, like thermoquiets. I also had factory appearing rotors with slots machined into them on mine since they were the same price as plain ones...

Excellent, that is the info I needed. Can anyone recomend a good place to get all these parts?

proportioning valve..... from ground up. (http://www.ss396.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=396&Product_Code=FM-1350&Category_Code=BRA-001)

Which is the same one (looks like it)from..
http://www.mpbrakes.com/mp8.htm

Home page for each:

http://www.ss396.com aka--- groundup. (http://www.ss396.com)

http://www.mpbrakes.com/

There are other choices so by all means shop around if you have the time.

John C.
Pensacola Fl
65 project wagon.

You can get the master cylinder and likely the booster from any parts store, if not a booster complete with mastercylinder is available from National Parts Depot for I think either 65 or 85 dollars...

the valves are available on several sites...the one for my car was $75 so I used the ones from the parts car instead

The major difference in a Disc/Drum master cylinder and a Drum/Drum M/C is that the bore is 1-1/8" diameter for the disc/drum versus the drum/drum which is about 15/16" this is required because stock calipers take much more fluid to move then to the drum/drum. Also, the disc portion of the M/C has a larger reservoir due the calipers requiring more fluid. Yes you also need to have the proper proportioning valve, but I suspect the prior issue was because of the Drum/Drum M/C. What happens is that you run out of stroke before you can fully apply the front brakes. With that smaller M/C you are losing 44% of the fluid in the larger bore M/C.

I have done this swap. I used an adjustable proporting valve, front brake hoses for a 69 Camaro so that they will mount in the stock drum brake hose clips, and a Master cylinder for a 69 chevelle with non power disc brakes. Calipers, Pads, hoses and Mastercylinder all available through Autozone. The Adjustable proportion valve was about $50.(available through Summit and the like) I tapped in inline after the distribution block and before it meets the rear block. It was an easy swap and definitely one of the best improvements I've to my ride. graemlins/thumbsup.gif

is the proportioning valve jsut to keep the back from locking up? Also, do i need a special master cylinder if im doing non-power discs? (when i can, id like to add the booster).

Thanks for all your help guys (and ladys)

Bubba
Heres my 68ss (first restoration/dream car that i have finally made happen---im only 21)
what do ya' think? any sugestions? Im trying to make it really nice, and i have big block all built up and ready to be dropped in next weekend!
web page (http://www.garsworld.com/chev/default.htm)

is the proportioning valve jsut to keep the back from locking up? Also, do i need a special master cylinder if im doing non-power discs? (when i can, id like to add the booster).

Thanks for all your help guys (and ladys)

Bubba
Heres my 68ss (first restoration/dream car that i have finally made happen---im only 21)
what do ya' think? any sugestions? Im trying to make it really nice, and i have big block all built up and ready to be dropped in next weekend!
web page (http://www.garsworld.com/chev/default.htm)

No the valve keeps the front from locking BEFORE the rear, I think the brake pads need less travel than the brake shoes to lock?

All I know is I had forgotten the rear valve and my car was doing nose dives just barely pushing the pedal, put the valve on and it stopped nose diving

The proportioning valve (or is it the combination valve?) does two things. It reduces the pressure to the rear brakes (so they do not lock-up because most of the weight is on the front brakes) and it provides a slight delay to the front brakes so that the rears apply first. It also has a switch built into it that illuminates a lamp in the dash to show if the system is unbalanced (meaning front or rear brakes aren't getting the right pressure). Anyone correct me if I screwed-up that explanation.
As for the M/C...you might need to change the M/C when you add a power booster as typically the Manual M/C has a different plunger on the back where the pedal rod fits in. I think the power booster normally uses a shorter rod and shallower plunger and the manual has a longer rod and deeper plunger. This is important to check because the wrong combination can cause either excessive pedal travel or your brakes are constantly under excessive drag (because the long rod and shallow plunger is applying the brakes some even with your foot off of the pedal).