Brakes locking while driving (LT35)

[Imatigur]

Hi guys i wonder if you can help me with this problem. After driving for a few miles/ minutes my brake pedal goes hard and the front brakes lock on, on their own. If i leave it a while it's all back to normal for a few miles and it starts all over again. Any ideas?:confused:

Van is an 2.5 TDI LT35 on an X plate (2000) with 120k on the clock.

[zollaf]

could be the master cylineder not returning enough so fluid is trapped, gets hot, expands, brakes lock on, cools down, brakes release. try lifting the pedal next time it happens and see if it releases them.

[Imatigur]

Thanks for the fast reply zollaf. The pedal has no movement, it's hard right at the top. Would i still be able to lift it?

[zollaf]

there has to be freeplay in it, the master cylindermust return right to the top of its travel. if there is no freeplay, its like you are applying the brakes all the time. has it had any work done in this area or did this fault just appear.

[Imatigur]

No work done, just started to happen. The only way i can describe the pedal is if the pedal has been pumped solid without the engine running so the pedal will not depress at all. I just tried it and there is no room for me to lift it, it's fully out.

[Imatigur]

Anyone else have any guesses? Would a fault finder flash up a code? Are there any electronic workshop manuals to be had guys??

[zollaf]

so next time they lock, undo the 2 nuts holding the master cylinder onto the servo. see if loosening them releases the brakes.

[Imatigur]

Cool, i will try that next Zollaf.....if it does release them what does that mean? Thanks so much for your help it is much appreciated.

[zollaf]

if it does release then its probably the master locking out for some strange reason, not enough travel keeping it closed inside, not allowing fluid to return. i would also un nip the connections onto it that go to the front brakes to see if that works. what i think is happening you see is that the master cylinder is simply not returning enough, so its like you are pressing the brakes slightly. faulty cylinder or faulty pedal. another test would be to try and push a cylinder back in a caliper, if it won't go back, undo things until it will, like the master from the servo, pipe connections etc.

[zollaf]

it could also be the front flexi hoses. they can fail internally and not let fluid return .

[Imatigur]

Zollaf, many thanks for the replies. I will try all of the above on Monday when i'm back home and report back.......have a nice weekend :o)

[zollaf]

no problem, happy to help, hopefully something will work on it. :)

[Imatigur]

Ok just tried it. For some reason it took longer to lock up this time, no idea why. They did eventually lock on so i released the two nuts that hold the master cylinder to the servo.....whoosh of air and i locked them back up. Jumped in, pedal still hard....fired her up and the pedal went back to normal and brakes working again.......took it for a spin and all fine (until it does it again)?? Is it normal that when i press the pedal it sounds like blowing an air-bed up with a foot pump? I think it has always done this though. Another thing, would there be any pipes behind the dash?

[Imatigur]

With the information so far does anyone want to hazard a guess on what part may be faulty? Servo, MC, Pump???