Bad wheel cylinder?

Northof49 · Posted: Wed Jul 16, 2014 8:02 am Post subject: Bad wheel cylinder?

I replaced my brakes completely, front to back. I have one rear wheel that every time I bleed that brake, it gives me air. I've gone over all the connections and there is no visible leakage. Brakes work fine, but pedal distance is further down than I'd like. The distance the pedal travels doesn't seem to increase over time. The other rear wheel cylinder never gives me air, just fluid. This one, always a puff of air when I have someone step on the brake pedal and I bleed it with a hose. Should I assume its the wheel cylinder drawing in air?
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1958 Karmann Ghia owner

PJ_1600 · Posted: Wed Jul 16, 2014 10:15 am Post subject:

Sometimes there is a stubborn pocket of air that just takes a lot a time and bleeding to get out. I've found that sometimes leaving it sit for a day or two will result in the air moving up and then a round or two will expel it. Another thing it to be sure all your shoes are turned out to the point where you can just barely (or not) turn your wheels by hand to maximize fluid space in the system - this will also help expel air. Lastly, if none of these work it could be a bad wheel cylinder. I've had that happen too when I (unknowingly) bought inferior (MiC) parts. I then got German made from WW and had no problems. Good luck.

Northof49 · Posted: Wed Jul 16, 2014 10:20 am Post subject:

My theory is that air is leaking in somehow. I figure that because after I expel air from the suspect wheel cylinder, the pedal doesn't get any higher. I'd expect that with every bit of air I get out, the pedal should come up. What do you think of that theory? The brakes work fine, I can make them squeal if I stop hard. Fronts are converted to discs.
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1958 Karmann Ghia owner

Mr.Duncan · Posted: Wed Jul 16, 2014 10:40 am Post subject:

Northof49 · Posted: Wed Jul 16, 2014 11:17 am Post subject:

Parking brake has no effect on my pedal. I have to try something, so it's a 20 dollar gamble to replace it. The right rear, when treated the same way, no air. I worry it's something to do with the junction block at the rear, but I can't find any leaking fluid there.
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1958 Karmann Ghia owner

Mr.Duncan · Posted: Wed Jul 16, 2014 11:18 am Post subject:

Northof49 · Posted: Wed Jul 16, 2014 11:31 am Post subject:

I can't recall what brand I bought. I bought them from CIP. I'm re-using my old, probably circa 1973 brake light switches. Still working!
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1958 Karmann Ghia owner

BUGGED11111 · Posted: Wed Jul 16, 2014 11:41 am Post subject:

If you have a cylinder handy I would just swap it and see how it goes.

I agree on the bleeder valves mentioned. I've had fussy ones that if I opened more than an 1/8 turn it would suck air and produce bubbles.

PJ_1600 · Posted: Wed Jul 16, 2014 11:50 am Post subject:

I gave up on the wheel cyls from CIP1 after getting two that leaked badly. Now pay the higher cost for German from WW. Ditto on bleeder screw more than 18th turn too.

Northof49 · Posted: Wed Jul 16, 2014 11:51 am Post subject:

I guess I can't rule out that its air coming in the bleeder valve when its cracked open. I do only open it about 1/8th of a turn.
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1958 Karmann Ghia owner

wcfvw69 · Posted: Wed Jul 16, 2014 3:57 pm Post subject:

How are you bleeding them? With the pedal or a power bleeder or a suction bleeder? Suction bleeders can pull the inner rubber cups over in the wheel cylinders. I've seen that before.

I use a power bleeder now and it pushes ALL the air out fairly quickly.
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Northof49 · Posted: Wed Jul 16, 2014 6:08 pm Post subject:

I am bleeding using an assistant to press the brake pedal, while I crack open the bleeder for a short burst.
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1958 Karmann Ghia owner

Rene60 · Posted: Wed Jul 16, 2014 8:03 pm Post subject:

I had a front wheel cylinder do the same thing. It wasn't leaking or showing any signs of leaking. I replaced it and that fixed the problem.

Rene60 · Posted: Wed Jul 16, 2014 8:04 pm Post subject:

I had a front wheel cylinder do the same thing. It wasn't leaking or showing any signs of leaking. I replaced it and that fixed the problem.

alexvw · Posted: Wed Jul 16, 2014 8:07 pm Post subject:

Have the helper press pedal 4 times, and hold it. While they hold the pedal crack the bleeder and let air out. If this doesnt work you may want to invest in a bleeder tool that pushes fluid through the bleeder screw up to the master cylinder. It will push all the air out through the reservoir.
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Hyperspace · Posted: Wed Jul 16, 2014 10:29 pm Post subject:

sometimes the nipple has too much play and will only work when turned out perfectly. A judcious glob of copper grease smeared around the base to seal the nipple to cylinder junction will usualy sort this out.
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