Help me troubleshoot a brake problem

[ksechler]

I rebuilt and modified my brakes. Here's what I have:

Stock Booster

15/16 Master from an '81 ZX (the right one with 2 reservoirs)

4-piston calipers with the proper, non-vented rotors

Rear disk conversion from MSA

Wilwood proportioning valve (to rear brakes)

New steel lines throughout

Braided lines to calipers

I bled the brakes at the master cylinder and each caliper; right rear, left rear, left front, right front. I actually bled them twice and there didn't seem to be any air in the lines.

The pedal can still be depressed to the floor but pumping it repeatedly will get me pressure and minimal braking (I'm not sure how much because the car is simply not safe to drive right now).

I adjusted the booster pushrod length. I have no idea if it is right, but I did it wrong and may have dropped the reaction disk, but before I tear the booster apart I would like to be sure that is the problem. Doesn't the pump up symptom indicate air in the system, though?

Is there anyway to know if the reaction disk is dropped without taking the booster apart?

[Zed Head]

Some of the conversions don't put the bleed valve at the top of the internal cavities. A bubble gets stuck above the bleed valve. Other people have actually removed the calipers and oriented them to get the air out, with a piece of wood between the pads to squeeze on if they can't get it on the disc, then reinstalled after they're bled. It's also possible to put the stock calipers on the wrong sides, with the bleed valve on the bottom.

I think that a missing reaction disc just makes the brakes more off/on. The reaction disc smooths application of the booster pressure, I believe.

[EuroDat]

It sounds like air in your system. I think its the position of your calipers. I would checks Zed Head's tips. Reinstalling the calipers with brake lines attached can be a PITA, but its the only sure way of getting the air out.

[ksechler]

Some of the conversions don't put the bleed valve at the top of the internal cavities. A bubble gets stuck above the bleed valve. Other people have actually removed the calipers and oriented them to get the air out, with a piece of wood between the pads to squeeze on if they can't get it on the disc, then reinstalled after they're bled. It's also possible to put the stock calipers on the wrong sides, with the bleed valve on the bottom.

I think that a missing reaction disc just makes the brakes more off/on. The reaction disc smooths application of the booster pressure, I believe.

Thanks, you were right. I had the rear calipers reversed right for left. I switched them and got a good bleed. There are still some other issues but I have pedal feedback now and the car stops when I back it out of the garage. I think I might have dropped the reaction disk in the booster and the throw isn't quite right yet, but I have made some progress. Thanks again for the help.

[mlc240z]

Also, when you rebleed the system, start at left rear then right rear. On the Z, the left rear is actually the furthest from the master.

[Diseazd]

Ksechler......You probably did drop your reaction disc. No problem....you need to remove the two nuts attaching the M/C to the booster. Now move the M/C over a few inches to gain access to the plunger rod (no need to remove hydraulic lines from M/C, they will bend and move easily to give you access to the plunger). Pull the plunger and rubber seal cover out of the booster. Shine a light in the booster......if you see metal where the back of the plunger contacts the booster, the disc has dropped. You can probably retrieve the disc with needle nose pliers, if not, make a small neck down on your shop vac and vacuum the little rubber circle out. Super glue it to the back of the plunger and reinstall everything. You may have to adjust the length of the plunger, but a booster with out a reaction disc will never be right.

Edited March 2, 2013 by Diseazd

[Jeff G 78]

If Guy's advice above doesn't do it, there might still be air in the master cylinder. Get a 6" long hose and put one end of the hose on the front MC bleed port and the other end in the front reservoir below the fluid line. Crack the bleed port just enough to flow and slowly pump the brake pedal up and down until no bubbles appear in the reservoir. Close the port and repeat for the rear port. Rebleed the corners LR, RR, RF, and LF.

[Diseazd]

Hi Jeff......The reaction disc isn't going to fix his pedal to the floor problem, but when he fixes his bleed problem, he'll need to follow my post number 6 or he'll face another problem. Regards. Guy