Spongy brakes...stilll

[JP Noonan]

About 12-18 months and 5000+ miles I put on rebuilt 320i fronts, a new 19mm master cylinder, and new SS lines. I removed the prop valve and put in a 911 "T".

Better, but still the rears draged and didn't do much of anything. I just now put on rebuilt rears (I re-built them, the pistons were good just coated with grime, I cleaned out the bore above the seal and flushed the caliper out. Replaced all seals). Brakes seemed to get worse. I re-bled the system 6-7 times over the next two days with the car level, using the two person method. I even bought a pressure "power bleeder" and the pedal is still mushy, the fronts lock up but the rears still don't do squat. The E-brake barly holds the car still. The only good thing is that now the rears don't drag. I used some NOS Textar rear pads that came from a PO, and set the vent clearence twice, once before and after several bleedings.

Am I doing something wrong? Is there a way to "bench bleed" the master cylinder that I didn't know about? Do I need a 22mm bus or a 23 Merc master cylinder?

I didn't turn the rotors, I will be replacing the fronts with new rotors in the near future. I've put new pads on old rotors before with no problem on other cars, but is this the problem?

Thanks

[Jim Smolka]

A couple of tricks for bleeding the brakes.

Check to be sure that the bleeder valve is above the piston... I mount my 5 lug rear brakes on the wrong side, therefore the bleeder valves would not let the air out.

I am not sure it will work on 914 rear brakes, but push the pistons in a little, and then bleed the brakes.

As always, just my $0.015 worth

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Smoke Daddy

[sammyg2]

Replace the brake lines. They do go bad. That is my guess, unless the venting clearance is way off. How does the e-brake work?

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Gerald Gore II (Sam)
73 914 350 small block

[JP Noonan]

Thanks

1. The rears have two bleeds per caliper. I bled the bottom ones first then the top ones. The fronts have the bleeders on the top. I'll try the pedal pushed in with the power bleeder.

2. Do you mean the hard lines go bad? I guess they could be full of corrosion but the fluid comes out clear. The hoses are brand new stainless steel braided kind. The P-Brake doesn't work well at all, but it never did. The vent clearence is set to .008"

[Dave at Pelican Parts]

JP, try setting the venting clearance to about half of spec. It may not be something that you want to drive around on all the time, but it may help take some of the slop out of the pedal.

Have you bled all of the calipers a number of times? Air bubbles in the brake system are notorious for magically transporting themselves from one end of the car to the other. Any air in any part of the system will make for a spongy-feeling pedal.

--DD

[JP Noonan]

hmmm.... I thought about tring that, since the rears used to drag so much anyway.

I learned my leason about bleeding the whole system a while ago. I did the front calipers on my truck and didn't see the need to bleed the rears when done. Exciting ride.

The action of the pedal is such that it travels about 3-4" before pushing back and takes another 2" before the fronts start to brake. I have the actuator rod adjusted, maybe this is just how 914 brakes are??? They do work, I'm just being picky.

BTW if I "pump" the brakes it doesn't help and if I hold firm pressure on the pedal it doesn't go to the floor.

Do I need to bleed the "T" connection?

[JTB]

I would check the tee. If it has any sort of loop in it, it could trap some air.

I think you will always have too much pedal travel though. I have M calipers on the front, rebuilt on the rear, and a 19 mm master cylinder and have too much travel in my opinion. No mater how many times I bleed, pressurized or not, I can never get a solid pedal with little travel.

[John Rogers]

Hi JP, I agree with Dave, set the vent clearance to 1/2 or less of stock spec on the rears ( I use 1mm). Once bled they should work and the E-brake should grab really tight. Since you did say the fronts are tight the master cylinder should be fine. Before starting, block one of the rear caliper brake lines till one side is hard then hook up the other and do the same. Remember since you had the pistons out and new seals installed it is going to take a while to make the seals creep along the caliper bore to find their resting place. The way I do this in a hurry is to loosen the caliper from the mounts and put a block of hard wood that is about 1/8 inch thinner than the rotor between the pads and then bleed. Then have an assistant stomp the pedal HARD and watch what the pads do. They will move out a little more than they should but this will simulate worn pads. Or you can use the old pads you took out, don't breath the dust!! Make sure the e-brake cable is adjusted to the new settings of the calipers. I usually start with the handle down and minimum amount of cable sleve adjuster "out" and proceede from there. Next I would make sure there were no sharp edges on the pad metal backing. I have seen some that would not barely move due to burrs. Finally, Tees have no loops or other hidden places inside so I would not worry about that and you don't need a 23mm M/C yet unless you do what I did with the 320i's on the rear too! Good luck.