Mk I Rabbit with super soft brake pedal

[280Z Turbo]

I'm actually posting about my race team's 1980 Volkswagen Rabbit.



The pedal almost goes to the floor, but you can pump it up to get it more firm. We replaced the master cylinder and bled it a bunch of times, but it's still really bad. The master cylinder pushrod is adjusted properly.

I suggested checking the rear drums to see if the shoes were out of adjustment. Anybody know of anything else?

[Raghavan]

Bad wheel cylinders that have too much slack so the pistons take a while to push the shoes out completely?

[280Z Turbo]

Bad wheel cylinders that have too much slack so the pistons take a while to push the shoes out completely?

Sort of. There's an adjustment on the rear wheel cylinders. If the shoes are too far away from the surface of the drums you have to pump the brakes up to get enough fluid back there to expand them that extra distance.

[Raghavan]

So it's the wheel cylinders then? I think that'd make sense. Too bad they're a PITA to replace.

[280Z Turbo]

So it's the wheel cylinders then? I think that'd make sense. Too bad they're a PITA to replace.

No, if that was the case (and we don't know that it is), then the cylinders would simply have to be tightened.

Wheel cylinders are easy to replace, BTW.

[Raghavan]

You can tighten wheel cylinders? I didn't know that. I'm still a n00b mechanic though.
And I thought it was a bit of a PITA to replace on a VW Bus.

[Raghavan]

Oh, and is the Rabbit in tripod mode in that pic?
That's so cool!

[280Z Turbo]

Oh, and is the Rabbit in tripod mode in that pic?
That's so cool!

It has a tendency to do that. It has a BIG rear sway bar.

It was doing it tonight.

[Raghavan]

Don't big rear swaybars make FWD cars lift oversteer?

[93JC]

Brake lines?

I think that's one of the first things I'd check. The rubber lines to the wheels moreso than the steel lines. If they're original, OEM lines they've probably gone to shite. Stainless, braided lines FTW!

[280Z Turbo]

I think they are stainless braided, but I will check.

[JWC]

I don't think you really tighten the wheel cylinders themselves, you adjust shoes which decreases their amount of travel.  Usually, there is an access hole for the star wheel adjuster on the backing plate.  Take a flat screw driver, or brake adjustment tool (looks like a flat head screw driver with a bend in it) and adjust the shoes till the wheel will not spin.  Then, back it off slightly until it has just a little drag to it.

[280Z Turbo]

I know how to do it...I've done it many times myself.

I'm asking what could it be other than that?

[S204STi]

Leaking wheel cylinders could do it.  Not sure if the vacuum assist would cause an issue like the one you mention, but maybe...

[JWC]

I know how to do it...I've done it many times myself.

I'm asking what could it be other than that?

Sorry, I was responding to Rag saying to "tighten" the wheel cylinders.


If you have already bled the brakes (and I don't mean just the master cylinder), I'd do as Ringe said and check for a leaking wheel cylinder (or two). 

If nothing seems obvious, I'd suspect a defective master cylinder and exchange it.

[280Z Turbo]

Those guys don't think it's the rear drums, but we'll see on Saturday.

I'll let you know what happens.

[280Z Turbo]

We adjusted the brake pedal pushrod fork. The only problem was that the stopper was missing, so the pedal stuck out rather far.

Much better than it was before.

[S204STi]

Cool!