Please confirm suspect master cylinder... I want to stop!

[Wildthings]

[BDorsey]

Ok, I've done it twice but I may not have them adjusted tight enough. I'll check again and see if that solves it. For reference, should I be able to turn the drums, wheels off, by hand when they are adjusted correctly?

I don't see any fluid coming from the rear cylinders. Or anywhere else in the braking system, for that matter. The fluid in the res has stayed steady.

Thanks much!

[Wildthings]

Sometimes it can take a bit of effort to turn the wheel especially if the drums are warped. If they are too tight the brakes will heat up and start to noticeable drag so it they are too tight it is make itself obvious pretty quickly.

[wesitarz]

[quote="BDorsey"]Hello all,
So I've changed the brake master cylinder (German FTE from Van-Cafe) and the rear brake flex lines then bled the system three times. But... the problem persists and actually feels a little worse. That is, the pedal is really soft and if I apply steady pressure it will sink until it feels like it hits something. I can feel and hear a knock coming from the MC when this happens (console is off still so I can see and touch the MC).
I did not bench bleed the MC but I feel I've done a thorough job bleeding with the pedal pump method.
I guess its possible that I bought a defective MC but I find it unlikely that it would fail in the exact same manner. I've read that a bad proportioning valve can cause soft pedal but honestly I don't understand how that would work unless there is a huge bubble in there.
Any suggestions? Thanks!!

I would take the MC off and bench bleed it,then re-bleed the whole system.Is it possible to damage the internals of a MC if it is not bench bled? Test MC by plugging both outlets and press brake pedal to see if it's firm?

[wcdennis]

I vote for a bad replacement MC. Even if your rears were badly adjusted, you should be able to pump the brakes and have the pedal get firm and hold solid. Bleeding brakes is not that tricky and it sounds like you understand the principal, I doubt you have air in the system.

[BDorsey]

"Even if your rears were badly adjusted, you should be able to pump the brakes and have the pedal get firm and hold solid."

"I would take the MC off and bench bleed it,then re-bleed the whole system."

These two ideas have been nagging me too.

I would expect the pedal to hold once the shoes were against the drum but even pumping the pedal doesn't cause this to happen. It always sinks to where I believe one of the MC's internal pistons reaches then end of its travel. The shoes are touching the drum without pressing the pedal so I would think it would be possible to get a firm pedal, even if it took a few pumps.

Is it possible that there is air still in the MC? I find that hard to believe since I've pushed a lot of fluid through it already but maybe bench bleeding is required. I could try this since I have to empty the reservoir again to replace the clutch MC.

Bummer... I was hoping I could just adjust the rear shoes and it would be solved. Maybe not, but I'll try that first.

I'll be disappointed if the new MC is defective. I haven't eaten the cookie the folks at Van Cafe sent with my parts yet. Do I trust it?

[Wildthings]

If the seals in the MC are bypassing fluid as in the pedal slowly sinks towards the floor the MC is faulty.

Sadly a fairly high percentage of new parts are bad right out of the box, nothing new here, always been that way.

[dobryan]

Yep, certainly could be a bad mc out of the box.
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[Vana Guy]

Any luck with the brakes?

Same problem here, pedal goes down a little bit, then seems to hit a hard metallic stop with brakes not fully engaged.

[BDorsey]

Hi Vana Guy
I don't know if our symptoms are exactly the same since my brakes engage fully and I have good stopping power. That said, I did replace the master cylinder again, after bench bleeding it, and bled the brakes thoroughly. I still had the same thing happening so I took it to a local German auto mechanic to get some expert advice. He drove it and said the brakes were some of the best he'd felt on a vanagon. I've been driving it all over the west, over 10k foot passes, local mountains, etc and have had no problem with the brakes even though I can still get the pedal to hit the solid stop. At this point I'm satisfied with the function and safety so I've decided to let it be.

This is probably not very helpful to you, sorry. But if you get any other answers I'm still curious to know exactly what's happening.

Good luck.

[Vana Guy]

Thanks for getting back. I have a new clue to my problem...
http://www.thesamba.com/vw/forum/viewtopic.php?t=662406

One thing I have been wondering, is it possible air can get trapped in the master cylinder since it is slanted and not level when installed into the car. Looking at it, there is some space from where the brake lines screw into the cylinder and the end of the cylinder which is higher than where the brake line screws in. It looks like air could get trapped in that space at the end of the cylinder.

[Ahwahnee]

[BDorsey]

If your pedal is really hard to move then I think the link you posted may be on the right track. But if its a soft pedal that seems to go too far toward the floor then that doesn't seem like a vacuum leak.