THSCC Forums

The Jetta has been having brake system issues for a while now. I had gotten used to the feel when I drove it every day but now that I'm not I know how bad they really are. The pedal is very soft and travels almost to the floor when I stop. I've bled the brakes twice, changed pads, had the master cylinder replaced and bled the brakes again and refilled with ATE Blue. The problem still exists. That leaves three possibilities that I can think of:

1) ABS controller. The ABS still works and there are no ABS errors on the dash, so I don't think that is the problem.

2) Brake booster. It passes the test in the Bentley manual.

3) Brake lines. The flexible brake lines are original and have almost 100k on them. I consider myself a fairly aggressive driver plus I've done several autocrosses in the car. I'm left thinking these have worn out and are expanding under pressure.

The calipers don't leak so I don't know what else it could be. Any suggestions?

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'99 Mk IV Jetta VR6 now claimed by the better half.

'90 Miata A-package, Floats like a butterfly and buzzes like a BEE with loudspeakers.

Assuming:

1) The master cylinder is new (rather than a different used one)

2) This is with normal use (i.e. fluid or pad fade is not an issue)

3) The abs pump cannot cause the problem. I'll defer to someone who knows about abs pump failure modes. I had a Ford/Bosch pump fail but it was "just" a massive leak!

Sounds like you either:

1) Have air trapped somewhere in the system even though you've bled it twice.

2) Have something causing excess pad travel at one or more of the wheels.

Possible causes of excess pad travel with old and new pads:

1) Loose wheel/hub bearing(s) causing run out which "kicks" the pads back.

2) Extreme rotor runout kicking the pads back at one or more wheels.

3) "Something" (technical term) wrong with the parking brake system that is keeping one or more of the involved pads from operating properly. Example, IF the parking brake is the type where the piston has some sort of slot that engages with the pad backing plate it may not be engaged properly allowing the pad to "rock" when the brakes are applied.

Booster should not be a problem since there should be a direct mechanical linkage from the pedal through the booster to the master cylinder.

Basically from what I know or think I know it is either:

Air in the hydraulic system, bad replacement M/C, or excess pad travel since pads should have almost no travel.

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Dick Rasmussen

FS 50 2018 Mustang GT

See also http://www.4g61t.com/thsccforum/viewtopic.php?t=1424

This is a thread started under Tech by Ryan Holton on May 5 if the link doesn't work.

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Dick Rasmussen

FS 50 2018 Mustang GT

There may be another cause for the problem here. If the Jetta has rear drum brakes there could be a problem with the adjusters. With a 100k miles they could be gummed up and not working.


My $.02

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George Bright Member # 141
One of the youngest of the old farts.
Yes I voted against you joining the club.

4 wheel disc brakes George. but thanks for playing

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www.ncvw.org
1993 VW Corrado VR6 - DSP15 (RIP)
1986 MB 190E 2.3L 16v - STX (SOLD)
1997 BMW M3 3.2L - BS for now

When I replaced a master cylinder and rebuilt 2 calipers on the BMW, it literally took 3 weeks and a DOZEN bleeds to get all the air out. It was all coming out as these tiny bubbles that I couldn't see unless I had a light shining on the clear bleed tube. I must have bled a gallon of brake fluid. Something to consider.

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

Just another idea...

If the ABS is full of air bubbles they are a bugger to get out. On one of my cars I ended up just paying the dealer to bleed them. They have a Tech something-or-other bleeding system. It forces the ABS on and off during the bleed and actually pumps the brake fluid out of the ABS. Just doing home bleeding draining of each corner of the car won't get the air out of the ABS. You can just spend weeks bleeding off a little at a time.

It's only happened to me once but it was worth paying the dealer to get it done.

Graham

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http://www.greywinds.com

Since Dick mentioned pad knockback as a potential cause, I thought I'd pass along this link on the subject from Stoptech:

http://www.stoptech.com/whitepapers/knockback.htm

I assume you have floating calipers so its less likely than in a fixed caliper system but the "tap the brakes a couple of times" test is pretty easy to try.


Frank

I second Dick's suggestion of looking at the parking brake. VW rear calipers are pretty notorious for parking brake problems. The parking brake operates with a funky ratcheting screw thing that (at least on the VR6) requires a tool to retract. They tend to rust solid from the inside out too, as the rears seem to collect water if not religiously bled once a year or more ofter.

--Kevin H.

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2003 WRX (again!)

Interresting! I'll look into that. Do you have VW rear caliper experience? What are the signs of rust building up? Would I not be able to compress the piston when changing pads? I don't have a proper tool for changing pads but should be able to get a loaner from Advance or Autozone.

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'99 Mk IV Jetta VR6 now claimed by the better half.

'90 Miata A-package, Floats like a butterfly and buzzes like a BEE with loudspeakers.

To quote Pat, thanks for playing Kevin, but nope .

The rear brake caliper issues were with early MKII's. They changed the design in the MKIII's. And the MKIV's, like Doug's, use aluminium rear calipers now.

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91 Jetta GLI STS/DSP 111
85 Porsche 944 ASP 11
http://www.blackforestindustries.com

That's interesting because my friend with the A3 GTI VR6 had parking brake probs almost exactly identical to those I had on the GTI 16v. But you definitely have a lot more late model VW experience than me. I'll take your word for it.

--Kevin H.

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2003 WRX (again!)