Kowal

71 442, power brakes, front disc.

Putting the car back together after doing a bunch of projects. It has a new brake booster from Brothers, new reproduction master cylinder (the kind with the bleeders), and new combination valve.

(Previous MC leaked, combo valve kept sticking, power brake booster seemed to be just a good idea)

Anyway...I am getting a very soft pedal and at the end of the pedal travel the brake idiot light goes on. The light goes back off as I release the brakes. I bled the brakes with a Mityvac, and bench bled the MC prior. Have no leaks that I can see. The booster is holding vacuum.

I know this is all probably describing air still in the brake lines. I am really just writing this out of frustration, after several hours and a large bottle of brake fluid gone. Should I just do the old fashioned wife pushing the brake pedal routine? I was surprised how quickly the Mityvac (the compressed air kind) emptied the reservoirs though the volume was so quick it was hard to see if the fluid was lacking air.

Tips? Doing the push the pedal routine, doesn't that cause the combo valve to slam one way or the other? Could this all be something else?

gs72

If you replaced the calipers, make sure they are on the correct sides. If the right and left calipers are mounted on the wrong sides, the bleeders end up being on the bottom of the caliper instead of the top. If this is the case you will never get the air out of the system. Unless you turn the car upside down lol.

Kowal

The calipers are untouched. Bleeders are on top of the calipers.

What got me started on the brakes, besides the leaky MC leaking out the back, was that it seemed as I drove the car when I got it that the brakes hung up a bit, with what seemed like more force up front.

gs72

Did you measure and match the pushrod height to the old master? A miss adjustment will effect how the fluid flows back to the master with pedal released. This could also effect bleeding.

oldcutlass

If your sucking all the fluid out of the M/C, all your doing is introducing more air in the system. You might try the ol fashioned way, which is my preferred method.

Kowal

On pushrod length. The new MC had a "shallow" pocket, the booster had the choice of the long and short pushrod, short pushrod installed as it came to me. Both are reproduction parts. So I didn't see a pushrod adjustment anywhere to be had (?). To the pedal, the clevis is set so the pedal was about a 1/4 to 3/8 of an inch from topping out when the pedal is released and at the top of its travel, the pedal has got plenty of room between it and the floor when pushed all the way down.

The MC was never empty as I used the Mityvac, I just did aerobics going back and forth from underneath to the MC and back.

So, did I do something wrong with the pushrod??

If I do the two person job, will the combo valve be a problem and how do I work around that??

Does gravity bleeding work and might that help??

Kowal

OK Following a tech tip on the Right Stuff website, I used a hose clamp and clamped the rubber hose to the rear axle that shut the supply to the rear brakes...and then started it up and tried the pedal. With the clamp in place everything was instantly fine...good force on the pedal, no brake light. So...I guess that tells me that I still have air in the rear somewhere, or maybe a bad rear wheel cylinder (guessing here). Will keep working it!

What really drove me in to this when I started was that I suspected that all of my stopping power was coming from the front as I test drove the car. Interesting.

tru-blue 442

You may have found the problem in
the rear wheel cylinders.
Do you see any oil slung out
on the inside of the rear tires?

gs72

The pushrod I was talking about is between the booster and the master. But it sounds like you have found the source of the problem. Neat trick isolating the front from the rears.

Kowal

Spent a bunch of time bleeding the rears, carefully and with great deliberation!

And it all works! Stops great. Good pedal.

Now on to the next issues! (Wipers don't work, ditto the radio, and I think it needs an alignment). Whew!