Need brake help, again

[BigRed76]

This has to do with the brakes on my '72 Cutlass. Its still GM brakes so i figured i could get some help with this.

I recently did an engine swap on this car, and that is where the brake trouble began. This used to be an all drum brake car but was converted to disc in the front so it has the distribution block on the frame below the mc. When putting in the new headers i had to remove the distribution block to get the header in, and then i reinstalled the block afterwards. I Then bled the brakes with no success (Excessive pedal travel & weak brakes). I then found a pinched brake line underneath the oil pan causing a restriction. I replaced that line and bled the brakes 2 more times, this time getting steady streams of fluid at all 4 wheels. But...there is still excessive pedal travel and the brakes do not apply until the pedal is nearly to the floor.

Could there somehow be air trapped inside of that distribution block?
Am i skipping something in the bleeding process?

Any input on this would help me greatly.

[chris71]

A few things. A distribution block is for 4 drum cars, pretty sure you need to switch to a proportioning valve for a front disc/rear drum setup. Also the MC needs to be for a disc/drum setup as well. Disc brakes require more fluid volume and less fluid pressure than drum brakes. Also, did you swap to power brakes? if so check the vaccum pressure to the booster from the mainfold. i think you need like at least 16 to 18 psi, since you changed engines this something to verify. low psi will equate to crappy brakes. if you disconnected the dist. block, did all the fluid drain out of the MC? if so you may need to bleed the MC. new MC's it is essential to bench bleed them. there is a way you can bleed the MC still on the car. how are you bleeding the car, the way that I do it is get a helper to be in the car, pump the pedal 5 times and hold, then you open a bleeder, to get the fluid/bubbles out then close, helper releases pedal. repeat.

[BigRed76]

The car has had disc brakes on it for about a year and it does have a disc/drum master cylinder on it. I didn't think about the engine vacuum even though there is a different engine now. The car has always had power brakes and the booster works great, it's just the brake pressure that's the problem. I have been bleeding the brakes as you described (helper pumping 5 times, hold pedal, repeat). When I removed the distribution block I do recall fluid draining out, so my issue may be with the master cylinder.

[BigRed76]

How exactly would I bleed the master cylinder while it is in the car?

[DKN]

These cars mount the booster on a large angle and can get air trapped at the end of the master cylinder bore. This is how I bleed the mastercylinder after it has been installed:

Unbolt the master cylinder from the booster. Position the master cylinder so the front is lower than the back. While the master cylinder is in this position compress the piston in one of the front brake calipers. (I usually wedge a screw driver between the caliper and the rotor and pull the screw driver with just enough force to move the caliper being carfull not to damadge the rotor.) This will cause the fluid to flow bacward thru the master cylinder. If you had any air trapped in the bore of the master cylinder it will be pushed out of the bore and into the reservoir. Then to bleed the rear circuit keep the front of the master cylinder positioned lower than the rear and using a blunt tool like a screw driver or a punch compress the master cylinder piston and release it several times. When you compress the master cylinder piston the rear wheel cylinders will extend. When you release the return springs inside the drum will compress the wheel cylinders creating a back flow once again pushing the air from the master cylinder bore up into the reservoir. Re-install the master cylider against the booster.

Danny Nix
CPP