soft pedal, hard pedal etc....

[1NASTY6]

Hey guys,

In a nutshell here is my problem:

With the Powermaster system on the car (87 GN) my pedal kept going away on me. I tried a new accumulator ball, same thing.

I bought a PM rebuild kit, and rebuilt PM with no problems, but when put back on car, same problem of Pedal going away on me.

Installed a power vacuum system on the car, and still had a pedal that would go away!
We have replaced Prop. Valve, bled the brakes till my leg about fell off, and still same problem. Oh yeah, we also changed Master cylinder at least 3 times now.

I changed out the booster, but evidently I put a bad one on, as the pedal went to a rock hard pedal.

Decided to go with MANUAL MASTER CYLINDER off of an S-10, and modified my pedal and used the "clevice type" adjustable rod out of a '65 Skylark and cut and grinded it to proper length.
(needed to cut and grind tip, but now it's adjustable, almost like what your adjustable wastegate rod is like. It uses a locking nut.)

You may have to do some adjusting etc. to get the rod to press the MC piston properly. Initially the rod was pointed to much skyward when the pedal was pushed, but with modifications, we solved that. Now pushes level with cylinder. Also, consider a "wedge shaped" mounting plate made out of 1/8 inch steel, that way your MC and tank will not be tipped down in the back (firewall side) so much. It takes a little manufacturing, but it sure looks good sitting in there level!

With Manual system, the pedal is better, only goes down about 1/2 way, but I still think something is not right.

We're going to try new calipers, shoes, and cylinders, but if that doesn't fix this issue.....

Anyone have this problem before, and if so, how did you fix it??

All ideas are welcome!

Thanks,

Tim

 

[gofstbuick]

I got tired of using my kids to help me bleed brakes, so I purchased a set of speedbleeders. They worked graet, then one day the pedal felt like it was going away. I noticed the some brake fluid on the inside of a front tire. I had one of my kids press on the brake pedal and noticed fluid leaking past the bleeder screw threads on the caliper. I suspect you may have a leak at a wheel cylinder, or caliper. Brake gauges may help, then you can test the lines and eliminate the hydraulic system leading up the the calipers and or wheel cylinders.

 

[BJM]

It sounds like your PM was not the actual problem. I remember a thread where someone mentioned how hard it was to bleed the rear brakes on our cars because the proportioning valve cuts flow off when there is too much differential pressure across it, like when one side is open. The solution there was to vacuum bleed at each brake. I use a vacuum pump and suck fluid out at each wheel and I have never had a soft pedal problem. Its also much easier to do than using the pedal. Its also the fastest way to bleed.

The speed bleeders don't fix this problem since you still use the pedal. Pressure bleeding at the master cylinder reservoir would probably work since the pressure is a lot lower than using the pedal.

 

[gofstbuick]

I took the speed bleeders out, replaced them with factory bleeders and have used gravity bleed and have not encountered any problems. There is a rubber cover that sits over the rod on the combination valve and it usually contains the rod well enough that if you bleed with the pedal, it' will usually not cause issues. But if you must, you can have someone hold the rod in while you bleed the brakes. Also, you could fill a container with brake fluid and attach a hose to it and connect it to a bleeder and pump away. As you pump the pedal, it will push out any air and when you release the pedal, the suction will draw fluid from the container (filled with brake fluid).