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I have a 2002 Volkswagen Passat 130 TDI Sport which I bought new as an import (Warranty expired) The problem I have started at the end of August when I had to make an emergency stop. The ABS cut in and the car stopped when I went to move off the car would not move and stayed like that for about 1 to 2 minutes after a click sound that appeared to come from the front of the car I found that I could move the car. I carried on my journey and found when I got to work that the rear offside caliper was binding. I managed to ease the binding but I have found that the fuel consumption on the car has dropped by about 25% and that from time to time the brakes appear to be binding, the rear offside caliper has been replaced and as a precaution the handbrake cable to this caliper was also been replaced. The fault still remains. The front calipers have been cleaned and cooper grease applied to the bearing surfaces. The car has had a thorough brake test by a local brake centre including an ABS diagnostic check and no faults were found. This is obviously an intermitent fault. I have been told that the ABS Modulator may be at fault and this would not have been apparent on the diagnostic check. I would appreciate any comments please help!
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Here's the starting point I would go from...
When you find the wheel is binding, is there hydraulic pressure in the circuit to that brake? i.e., can the binding be relieved simply by opening the bleed valve?
If this is the case, then you are looking for something upstream of the wheel. If the other brake on that circuit is not similarly pressurised, that would clear the master cylinder from suspicion, and would focus attention on the ABS unit.
number_cruncher
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Let me get this right. When binding takes place I need to check whether both the front nearside and the rear offside are binding, if I can release the front wheel by opening the bleed valve and the rear wheel also releases you are saying that the master cylinder is probably the fault.
With reference to the master cylinder when the brakes start to bind the brake pedal does not have as much play and the brakes comes on with a smaller than usual depression on the pedal.
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I don't know how the braking circuits are laid out on this car, but the brakes on the same circuit are fed from the same piston on the master cylinder.
If it does point to the master cylinder, you can get the car to bind up again, then loosen a brake pipe on the appropriate piston on the master cylinder. If that frees both brakes, then you have diagnosed the master cylinder.
Likewise, loosening the appropriate pipe downstream of the ABS unit may help to pinpoint the fault to that unit.
While the method is a bit of trial and error, it will allow you to find the faulty component, and have more confidence that replacing it will cure your fault.
I agree with Aprilia's excellent suggestion of considering the flexible pipes, it's not unknown!
number_cruncher
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This morning the brakes started to bind so when I got home I released the presure at the master cylinder. The wheels were no longer binding after the presure was releasesd. I've ordered a new master cylinder which I shall fit tomorrow. Fingers crossed!
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Hi Ralph,
When fitting your new cylinder, make sure that there is clearance between the pushrod and the piston. If not, the fluid can't get back into the reservoir, which can cause binding.
number_cruncher
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I assume the clearance is governed and adjusted at the pedal end.
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Hi Ralph,
I'm not sure. There can be adjustment at the pedal, and within the stub of the pushrod in the servo. Both, obviously need to be right!
number_cruncher
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I took the master cylinder off yesterday and found the servo had about 1.5l of water in it and the plenum chamber had about 2l of water in it the drain on the plenum chamber was blocked with black silt. The servo fell to bits so I had to get hold of a new one. Fitted a new servo and new master cylinder and as yet all seems to be correct.
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My wife's got a passat 2001 130 sport with what sounds exactly the same problem you car had. The initial problem (last week) was the brakes sticking on as per your problem. Recently though the brakes aren't as responsive as they were and the acceleration is sluggish and the brakes bind. I've changed discs, pads and fluid today as it needed doing but this hasn't helped. Can you let me know if changing the master cylinder / servo fixed the problem. A response would be greatly appreciated as i'm booked in with VW but would prefer to do it myself. Regards Mark
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When you found the rear brakes binding was the correct tool used to retract the pistons into the calipers? If the pistons were pushed back into the caliper without being rotated at the same time then permanent damage and/or seizure could result.
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The piston was not forced back but the caliper in question has been replaced and I still have the same problem.
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I have seen this before on another vehicle and it was indeed the ABS electrohydraulic modulator (a sticking solenoid). Do check for other things first though - like one of the rubber brake hoses collapsing internally - I've seen that too.
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