200 TDi Brake problems

alright,

Just a quick question, do you think these symptoms point towards a faulty brake master cylinder?

Since about 2 weeks ago, the brake pedal seems to have a lot of travel, feel soft and reduced braking efficiency one minute, then hard, hardly any travel and good braking (which is how it has always felt) the next, not depending on engine revs.

The front callipers, rear cylinders and all brake pipes were replaced in august 2010. There is no bulging in the flexi pipes, and no leaks anywhere, even though the master cylinder had lost about a table spoon of brake fluid, since the brake overhaul in august 2010.

I pressure bled the system today, no air bubbles came through. But the pedal still seems to be good one minute and soft the next.

The master cylinder does make a "puffing" noise when depressing the pedal.

Does this sound like a faulty master cylinder??

Any help appreciated.

thanks

Joe

well. I get the puffing noise too, and my brakes work brilliantly, so I wouldn't worry about that as a symptom in itself. I had a hyundai once that almost killed me by having great pedal resistance one minute, and then no resistance at all the next.. the travel went to the floor! That was the master cylinder, so I reckon you're on the right track personally. I think a test you can do is to put your foot down on the brake quite hard, with consistent pressure, and if the pedal keeps on moving to the floor, then there's a problem with the master cylinder internally.

i had a similar thing happen to me whilst on a family holiday, as i didnt have any tools with me and knowing i may be ready for brake pads i ignored it until i got home.
Sometimes the pedal would travel further than normal and required pressing again to get a full pedal. It turned out that a wheel bearing had colapsed and the wheel had enough movement to push the pads apart. There was no indication anything was wrong with the bearing and the journey home probably worsened it more. Worth a try as you have overhauled the brake system recently

Have you tried adjusting the rear shoes up?



Lynall

It's a fair point. Depends on the consistency. if you have long travel on the first press and then it stiffens on the next, then it could be that the shoes are too far out, or something else causing pads or shoes to be pushed away like top cat said. if it appears to be random, with no way to predict the behavior, then that sounds like what happened to my Hyundai.

yeah i adjusted up the rear shoes. The adjuster only went round another click. The pedal is really random. Its fine for the first few pedal usages, then seems to become random after that. I think it might be pointing towards the master cylinder, like tombardier's Hyundai.

Ive also had slack wheel bearings which allow the disc to knock the pads away from the disc causing long travel.



Lynall

tombardier said:

well. I get the puffing noise too, and my brakes work brilliantly, so I wouldn't worry about that as a symptom in itself. I had a hyundai once that almost killed me by having great pedal resistance one minute, and then no resistance at all the next.. the travel went to the floor! That was the master cylinder, so I reckon you're on the right track personally. I think a test you can do is to put your foot down on the brake quite hard, with consistent pressure, and if the pedal keeps on moving to the floor, then there's a problem with the master cylinder internally.

Click to expand...

I'd try that test, my merc's master cylinder went on the clutch but, that test would only work if I applied fairly light pressure. If I pressed the pedal so the clutch disengaged the pressure wouldn't drop. However if I rested the weight of my foot on the pedal and didn't actually depress the pedal, it would sink to the floor.

Does sound master cylinder like if everything is adjusted as should.

All the wheel bearings have only just recently been replaced (in last 6 months), and there is no play in them what so ever, so I can’t see it being them.
The only thing, but it’s a long shot, that may be causing the pads to knock away from the disc, is that I stretched the springs that are meant to stop the pads from rattling in the callipers, as the pads were rattling really badly, but I can’t see the little springs that slide on split pins that hold that pads in place forcing the calliper pistons back in, or could they??

Anyhow, I’ve ordered a new master cylinder, and should be fitting it on Saturday, so time will tell.

thanks

no, but it was a long shot