brake troubles

[Chad Rhodes]

I'm working on my 92 camaro stocker which has all stock brakes, except a mopar master cylinder and line lock. There is no proportioning valve. I replaced the master cylinder because it was leaking. Prior to that it had brakes, but wouldn't hold the car very well on the starting line. I have bled the brakes repeadedly, i bench bled the master cylinder, but i still have no rear brakes. Anyone have a suggestion?

[Greg Reimer 7376]

I would be suspicious of the master cylinder. If it worked before you replaced it, and theres no air in the system, it sounds like the seal around the rear portion of the piston in the master cylinder isn't holding any pressure in that half of the system.

[Chad Rhodes]

I think i have figured it out this morning. The old master was leaking, but its a new car (new but sat for 5 years before we acquired it). Took the car to test, and it wouldn't hild very well in the lights, found a small seepage of fluid at the back of the master cylinder. Replaced master, problem still there. Just to double check i looked at our other stocker (vette) and noticed that the lines were reversed on the master. Now if I can just chase down the correct fittings so that I can swap them. That would explain the car not holding very well on the startinng line, but still stopping reasonably well

[Greg Reimer 7376]

In review, it's possible that the positions of the master cylinder reservoirs could be reversed. Drum brakes are self-energizing,meaning that as they apply, the front shoe is pulled into the rotating drum,thereby activating itself and pushing through the brake adjuster star wheel on the bottom, the lower end of the rear shoe. They require a volume of fluid to work, where disc pads are applied through pressure.Disc brakes require only a small amount of fluid under high pressure to work. Make sure they can release rapidly even if it means removing any pressure retention valve or device in the m/c where the line goes on.Drums and discs would not be compatible on a single master cylinder, like a 66 Chevy or something like that. Before adequate enough stopping power for the front brakes could be achieved,the rear tires would be up in smoke.The only exception to that rule I ever saw was a 65 Triumph Spitfire that a friend of mine has. The rear w/c's are probably 1/2" in diameter, and the front caliper bores were fairly large.On a British car like that, you don't buy rebuilt calipers or wheel cylinders-they sell you a seal kit. I went through the whole system on that car, and it worked fairly well. It was different, but I don't care to be an authority on how they build cars over there.Hopefully,your project will be easier to sort out.The large reservoir on a tandem master cylinder is for the disc brakes, the small one is for the side with the drums.

[Chad Rhodes]

both resivoirs appear the same (mopar style master), but i think there is a difference in the internals.

[RonM]

My instructions from Jegs on a mopar style master cylinder say that the rear port on the master cylinder (primary) should be connected to the end with the greatest total effective piston bore area. On my 85 camaro this is the smaller diameter line that goes to the front calipers. The rear brakes have the larger diameter line. I hope this helps. Ron

[GTX JOHN]

Mopar Masters come in different bore sizes and front to back proportion ratios (see Mopar Perf Cat. With my Wilwood Front and stock drums back ended up with 61 Frt. and 39 Back Master and I think 15/16 Bore for best holding

[Kris Kristofferson]

Is the pedal "high&hard"? What is the diameter of the master cylinder bore? I
f the master has been changed, did someone make sure the pedal is in the right position? ie a slot for manual etc to change leverage point??
If you want to get into it you could get a brake pressure gauge and diagnose..

[Kevin Lang]

Chad, Does this car have stock style brake hoses on it ? If it does then you need to put new ones on because when a vehicle sits that long without being used the brake hoses will swell up on the inside and close passage of fluid. My tow vehicle sat for 4 years and when I tried to bleed the brakes I got very little from the front and nothing form the rear. I hope this helps you. good luck!!!!! p.s. Keep it shiny side up!!!

[Chad Rhodes]

i got it figured out. Part of the problem was it had too big of a master cylinder, the other part was that the pushrod was in a bind. fixed those two things and its wonderful now.