Changed pads\discs all round on my golf mk2 at christmas. Also had to replace both rear brake calipers. After this, the brakes rocked!
Then about a week later, the brakes were spongy & alot of travel on the pedal. Re-bled the brakes & the rear ones had air in them. After this brakes back to good working order.
Now, a month on i've had the same trouble, spongy brakes & excess travel on pedal. Bled just the rear brakes at the weekend, got some air out & brakes are good again.
Can't work out where the air is getting in. If it's the master cylinder, then i would have thought the front bakes would have had air in as well(the brake system is one front\one rear off each line out of the master cylinder).
I thought it would be the rear brake compensator, but no obvious sign of leak behind the rubber seal (if air is getting in, then likely that fluid is getting out, right??).
Also, checked one of the new rear calipers & had a look for fluid behind the rubber seal - no sign!
Now waiting for a while to see if the brakes screw up again & i guess i'll have to start swappig out parts!
Any ideas??
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Not an expert, but a similar problem in my old Polo. To quote Bob Dylan 'it brakes just like a little girl'.
Racking my brains, IIRC there was a leak going into one of the calipers, or certainly at the rear wheel end of the system. The leak caused the fluid level to drop below the mimimum, which lead to air in the system.
You mention you've checked one caliper - what about the other? My mechanic, who knows his stuff, told me that this was a common problem in the car.
HTH. If not, give me another shout and I'll ask Mr Mechanic when I see him next week.
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Thanks for the info. The brake fluid level doesn't seem to drop, definately not below minimum. I'll check both calipers out properly if it happens again although being brand new, I'd hope they are ok. Guess it wouldn't be the first time new parts have been defective though!
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This may not be related to your problem but I've been told that bleeding brakes using the pedal as opposed to an easybleed can lead to problems due to excessive travel of the piston in the master cylinder. The theory (I'm told) is that seals move further than normal in the bore of the cylinder coming into contact with and dragging back any corrosion in the usually untouched part of the bore. This then damages the seals which then leads to rapid failure. I know of several instances of brake failure following bleeding of the brakes.
Doesn't really fit with your problem in that your brakes come back up after more bleeding. A full swap of fluid using an easybleed may be worth a try - assuming you didn't use this method in the first place.
Steve.
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It may not be relevant to this car, but I have several times had the symptoms of air in the system (ie spongy pedal) and it was the master cylinder seals starting to leak.
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I thought it could have been a problem with a faulty master cylinder after i bled the brakes - originally bled it via the pedal, then 2nd time using an easybleed. The fluid has been changed during this process.
The only thing that possibly contradicts this is that i only seem to get air in the rear brakes. As the master cylinder has 2 lines coming from it & these go to one front & the opposite rear, i would have expected air in the front & rear. However, maybe there's some law of physics out there that will explain this!
Someone else has suggested i push the pedal down hard & wedge it in place with something to keep pressure in the system, then leave it for a day or so. Afterwards inspect the system for leaks. May try this when i get a few days off?
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Hi Spoiler,
I can confirm that the pumped up and loaded brake pedal method seems to remove any air I cant get out by normal bleeding methods. 24 hrs is the usual time needed. Definitely well worth a try in your case, as it should also reveal any leaks as the previous poster suggests.
Good luck.
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Spoiler.
Trying to work through the fug of time but in the Polo again, the manual said that the most air will be extracted from the wheels furthest away from the cylinder. If you have time to do only one, do that one (one pipe only).
The rest is logical to me - front engine car. Rear wheels will always have the most air in the system.
HTH again.
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