Chevelle Brake Problem

[Damien]

I have just replaced my booster prop valve, master cylinder and the lines from the distribution block located on the chassis rail to the master on my 70 SS Chevelle. The booster and prop valve are restored items from Brake Boosters and the master cylinder is repro single bail 70 style with bleeders that came from Ground Up. The booster came with both long and short pins for the master and I installed it with the long pin as the master has the deep hole in it rather than the indentation that is for the short pin. So I change everything over, bleed the brakes, and the pedal just about hits the floor before they barely engage. Ok, do some searches, perhaps the rod out of the back of the booster to the pedal is a fraction long in adjustment and is hanging the master open? Adjust that, seems ok, gravity feed the brakes as I'm home alone, still the same! Now I'm getting fluid to all 4 corners, no problem. There should be no need for shoe adjustment, wheel cylinder replacement, any of that, doesn't leak and as 2 days ago everything worked great with the old set up. Obviously it's something I have or haven't done. Any help is greatly appreciated.
Thanks!

[Damien]

Is it possible the pin could be a little long and hanging the piston open in the master?

[Zman1969]

I replaced a booster and master on a 69 Firebird frt disc car with repo parts, I had to shorten the pin so I shortened the long one first (this way I'd have 2 chances)it had to be shorter than the short pin IIRC I took off over 1/4" gotta love aftermarket parts - sounds like it needs to be a little longer?
when you bolted the master to the booster did you have to push it back to get the nuts started? then the pin would be too long as was my case. you verify the booster is in the correct hole on the pedal?

[DWR]

I had the original master cylinder sleeved on my 70. I installed it and bled brakes at the wheels, could not get much pedal. I ended up pulling master cylinder and bench bleeding it, reinstalled and bled wheels again. Problem solved.

[m22mike]

Always, ALWAYS, bench bleed a master cylinder. I use some old hard lines bend up to the bottom of the reservoirs and leave them in place while bolting the MC down.

[jasonL78]

X2!!!!!!!

[njsteve]

X3. Without a bench bleed prior to installation, you will never get all the air out of the internal ports in the master cylinder.

[m22mike]

Not that this is Damien's problem, but I was just talking to Phil Woj on getting a good pedel on one of his projects.
One thing I told him to check was to make darn sure you have the back brake shoes adjusted, to much slop there and you may end up with lots of pedal travel and it may not be air.

Mike

[Damien]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Zman1969</div><div class="ubbcode-body">I replaced a booster and master on a 69 Firebird frt disc car with repo parts, I had to shorten the pin so I shortened the long one first (this way I'd have 2 chances)it had to be shorter than the short pin IIRC I took off over 1/4&quot; gotta love aftermarket parts - sounds like it needs to be a little longer?
when you bolted the master to the booster did you have to push it back to get the nuts started? then the pin would be too long as was my case. you verify the booster is in the correct hole on the pedal? </div></div>

Apologies everyone, I should have added that I did bench bleed the master before installing it.
Zman, I will check the pin length again as it could be the problem even if it hangs the piston open a little. The booster rod is in the correct (bottom) hole in the pedal.

[Woj]

FWIW,

I used a repop master cylinder on a past 69 Chevelle project, bench bled the heck out of it and never got a pedal. Put a rebuilt on in, bench bled and it worked like a champ. There is a chance you might just have a bad MC. Try another from a parts store (they are cheap). Or, maybe your old one if it worked.

Good luck.

Phil Woj.