[68SS396]

Here's the deal. Last year car had new power booster, new master cylinder (original style with the bleeder screws) and pretty much all new brake lines. It was front disk and rear drum. Car stopped great. Put in new rear end and added the conplete rear disk setup from a 79-81 Trans Am. Added a Wilwood adj pro valve from Summit at the same time. Now the pedal goes to the floor. The car will stop but the pedal goes right down. Pumping doesn't change anything. I've flushed so much fluid through that there is no way they need to be bled. Even bled the master cylinder again and again. Playing with the adjustable pro valve doesn't change anything. What am I missing? Do I need a different master cyl.? If so which one is a bolt on? The rear strapped me terribly for cash and don't want to buy parts hoping it fixes the problem, then it doesn't. Especially when everything is new. One rear caliper is new and everything is in mint condition with new pads. The large nut on the back of the rear calipers are turned snug so there is no extra travel. I know this is pretty straight foward so what am I missing? Please help

[elcamino72]

The only thing that I can suggest is to Bench Bleed the master cylinder. You have to have air in your system, thats about the only thing that would cause this probelm, I think. I suppose it could be a probelm w/ the proportioning valve, but I don't know.

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Bryan Shook
Burgettstown, Pa

[elcamino72]

I almost forgot. Do you have enough vacuum getting to the booster? I believe you need to have intake vacuum going to the booster.

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Bryan Shook
Burgettstown, Pa

[68SS396]

Thanks for the response Bryan. Yes I do believe the booster is getting enough vacuum. It is hooked up directly to the intake. The only things that changed since the brakes don't work is the rear with the disks and the adj. pro valve. I have tried bench bleeding also. I have gone through five quarts of brake fluid bleeding everything at least once and finding out about the bad caliper and bleeding again. Its almost funny. Frustrated as I am I have to laugh. Its the only thing I can think of so I keep doing it. Although I always thought that if they needed to be bled that you would be able to pump them to get a pedal feel for a few seconds then the pedal would go down. Mine goes down right from the beginning and they don't pump up at all.

[Joseph]

I don't know too much about brakes but I'll ask a few questions here and maybe they can get you on track.
Is the new master cylinder you purchased for a front disc/rear drum car? I believe that for rear disc cars the master cylinder needs to have a larger rear sump to accomidate the larger amount of fluid it takes to operate disc calipers. Where I'm going with this is I think the master cylinder does not have enough fluid volume to operate the rear calipers, thus excessive pedal travel.
Also, when you changed the brake lines did they have the same inner diameter as the originals? If they are larger then we are dealing with a new system which needs more fluid. This could compound the issue mentioned above.
If you are in anyway unsure as to the presence of air in your system have it power bled. It's the only way to make sure there is no air in your system.
The proportioning value only regulates the amount of fluid movement and should not create your problem unless it leaks.

Hope this gets you going in the right direction.

Joseph

[DOUG G]

did this start when the new power boster was installed? make sure the rod is in correct hole on brake pedal and is the rod long enough?and one more thing isn't there a special proportioning valve for that set up?

[68SS396]

One of the rear calipers has started to leak out of the cap in the middle of the piston so I had to buy a new one. Just picked it up today and installing it tonight. Don't think it is the whole problem but I can't diagnose any further until I fix this. I will let you know how I make out after doing this.
Doug, Everything mentioned was new about a year ago or so and was working great and the only thing that changed was the rear end and rear brakes and adj pro valve. Yes there is a special pro valve for 4wheel disk. I bought a adjustable one that does the same or better. I am tempted to think its the master cylinder but I know of many that have done this without changing it. We'll see what happens tonight when I replace the caliper. Thanks for the responses. I appreciate it.

[Bri]

I just put a power front disc brake system from Master Power on my camaro. When I asked what I would need to change if/when I put rear disc brakes on they said I would need a bigger power booster. If I read everything you wrote correctly your booster is matched to a disc/drum combo. Maybe a booster from a disc/disc set up would do the trick.

[68SS396]

Bri, Interesting. I haven't heard that before . Maybe I will go to a parts store and see if they list different part numbers. I ended up replacing both back calipers and the pedal feels a little better. It still seems to go alot further down than it should. Funny though, the car stops really good but the adj. pro valve doesn't seem to make a difference no matter what position I put it in. Even with full pressure to the back the car seems to still slightly nosedive when braking hard. Maybe something is wrong with the distribution block? Would that have a effect? I have the rear line running from the master cylinder to the pro valve to the dist. block then to the rear. Should I bypass the dist block for the rear? I guess I don't really know what its for.

[MikeDF80]

The master cylinder for drum/disk should be different from disk/disk. THis is because you need more volume per pedel stroke for disk brakes due to the large piston size.

[68SS396]

Mike, Unfortunately deep down this is what I expected. Has anyone done this or know what master cylinder is a bolt on? The rear disk setup is from a 79-81 TA. Does anyone know if I can use the master cylinder from one of those cars?

[MikeDF80]

The master cylinder from the car that you got the rear out of should work. Just make sure that the front calipers are similar, they shoud be. You will run into problemsif the T.A. front calipers had more pistons than your current calipres. I highly doubt this though. You can also can one of the aftermaket brakesources, and they can get you hookedup. I am 99 percent sure the T.A. should work.

[68SS396]

I can't believe how cheap those master cylinders are!! I just priced one and it was 18.00 with a 7.00 core. They had a better brand for a little more but I am experimenting here so there is no need at this point. If I get time I will pick it up anf try it tonight and let you know tomorrow. Thanks for the tips

[68SS396]

Bought the mster cylinder, bench bled it and put it on. Had to cut the pushrod coming out of the booster about a inch to work with this unit but besides that it was a bolt on. Here's the wierd part. Never have I ever undone a bleeder screw and had vacuum in the system. I found out by submerging the bleeder hose into a container of brake fluid, then opening the bleeder. It would actually suck up the fluid in the cup (rather quickly) instead of bleeding out air or fluid. That was a first. I had to bleed the rears by pushing the pedal down first then opening the bleeder. I could watch it squirt out when I opened it then it would come out slower until it would stop and actually start to suck up in a little. I bled by not waiting until that point. Did both backs that way and actually started to get a decent pedal but I didn't get a chance to do the fronts or start the car to check the feel. Too late and my car is too loud. Anyone ever heard of vacuum in the brake system? I'll see what happens this weekend if I can but have a Wedding on Saturday to go to and a swapmeet at Stafford Motor Speedway Sunday in CT. Great swapmeet

[68SS396]

Took the car around the block last night. Pedal is there and the brakes worked great. As good as my wife's Stealth. Ahh its like a new car again. Thank you everybody for the responses. Life is good again.