weak brakes

[Stovepipe]

I just got my car back together after a motor swap (1970 240z). Let me begin by saying my brakes worked fine last year when I parked the car. I had the front lines, MC, and booster out of the car for an engine bay repaint, and everything went back in when done.

Now after re-assembly, the brakes are weak. High pedal effort is required for even moderate stopping power. The pedal is fairly hard without spongyness, but it does have longer travel, and there is less than half normal braking power when i push as hard as I can.

In addition, the brake warning light on the dash comes on with anything more than light effort on the pedal, so basically anytime the pedal is depressed. I've read about what that means but I have not been able to find the cause of the pressure differential that would cause the light to come on, but I naturally believe this to be part of the problem.

So far I have done the following: bled and re-bled the MC and then the lines in proper order, rebuilt the front calipers with new pistons/seals, and took apart the booster in search of the elusive reaction disc. It's still in its bore, where it's supposed to be. The check valve in the vacuum line from the manifold is installed the right way and works fine. The rear drum pistons are not seized. There are no leaks in the hydraulic system that I can see.

Any suggestions on what is wrong?

Thanks,

Phil

Edited August 8, 2011 by Stovepipe

[Walter Moore]

1. Are the bleeders on the top of the calipers?

2. Is there a chance that you let the pusher disk (not sure what it is called) in the brake booster slip out of place when you put it all back together?

3. Could you have put the check valve in the brake vacuum hose in backward, or have a serious vacuum leak?

Edit: skip 2 and 3 you have that covered already. I suggest you look for a vacuum leak.

Edited August 9, 2011 by Walter Moore
Can't read apparently...

[Stovepipe]

The bleeders are on the bottom of the calipers. I should note i had the weak brakes before removing and rebuilding the calipers (I thought that might be the problem since the car sat for so long, and it did need a new brake piston, but no luck curing the problems).

Thanks for the reply Walter.

[beermanpete]

The brake warning light indicates low pressure on 1 of the 2 circuits.

The bleeders should be at the top of the calipers. You might have the right and left calipers reveresed. This will not allow you to get all the air out.

I suggest swapping the calipers side to side, rebleed, and test again.

[Stovepipe]

Yep, I reversed the calipers when I put them back on. I switched them back and re-bled them and now they work great, and the light is out. Thanks guys.