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[TheBoy]

TBE has a problem with its brakes, where I feel there is too much movement in the pedal, even by Omega standards (granted, I have got more used to the Jag's Ford-esque style brakes over the last few months, as I don't drive TBE much).

Initially I thought the brake pedal was creeping all the way to the floor, but now I have sufficient mobility back, I've had a better look.

Ign off, brake pedal moves and becomes nice an solid, without any pumping etc.  Start car, and as expected, the pedal drops a little lower, BUT continues to creep down until its about an inch from the floor (well, mat).

I have bled the brakes (and changed front pads whilst there, not that that matters for this discussion), the old fluid was quite dark for fluid that was about 3yrs old  .  I have activated the ABS return pump more times than I can remember.  Tech2 activation of each wheel shows no specific wheel is worse than others...  ...in addition, then testing each wheel, there is a fair amount of pedal movement when going from reducing brake pressure to each wheel, to allowing brake pressure to each wheel.


Running out of ideas, and time before the MOT is due.

Is this an MOT failure, ie to much brake pedal movement (but it doesn't sink to the floor)?


Any answers on a postcard please.

[VXL V6]

Had similar before and believe I ended up fitting a new master cylinder.

[Nick W]

Had similar before and believe I ended up fitting a new master cylinder.

that's what I would be looking at.

[TheBoy]

Tinterweb seems to imply that if it doesn't creep without servo assistance, it cant be master cylinder?  But then the internet is full of shite.

Any way of proving before going down that line?

[cam.in.head]

If you hose clamp both front hoses and both rear hoses and try the same pedal test this will confirm master cylinder is faulty. Providing of course that there are no leaks from any unions or pipes or from the abs block.the fact that the pedal creeps down with servo assistance is probably only because it is easier to press.if it doesnt creep any more now you can release each hose clamp seperately to find a faulty corner if req

[TheBoy]

If you hose clamp both front hoses and both rear hoses and try the same pedal test this will confirm master cylinder is faulty. Providing of course that there are no leaks from any unions or pipes or from the abs block.the fact that the pedal creeps down with servo assistance is probably only because it is easier to press.if it doesnt creep any more now you can release each hose clamp seperately to find a faulty corner if req

That's effectively what using tech2 does, but by using the ABS unit, not hose clamping...  ...and I ain't got 4 sets of molegrips . The results seems to imply all 4 have air in, even after bleeding, which is unlikely.  When I first did the test, as soon as I did the first caliper, I immediately though that that had air in.  Then the 2nd one. Obviously by the 4th, I was doubting things....


If it was master cylinder, would pedal sink to floor though?

[TheBoy]

Should point out, no visible leaks (apart from where I bled etc), and fluid level is stable.

[cam.in.head]

It still sounds like the master cylinder to me .if there are no other leaks and the fluid does not go down.( you could clamp the front hoses first and then do the rears if you have only two clamps !) to do the previous check.The master cylinder can fail in two ways.either fluid leaks out of the back and into the servo but this would cause the level to drop or it can leak internally.ie the seals leak fluid past themselves in the bore. Hence the piston will slowly move though the fluid / bore but none will actually be lost anywhere.

[TheBoy]

It still sounds like the master cylinder to me .if there are no other leaks and the fluid does not go down.( you could clamp the front hoses first and then do the rears if you have only two clamps !) to do the previous check.The master cylinder can fail in two ways.either fluid leaks out of the back and into the servo but this would cause the level to drop or it can leak internally.ie the seals leak fluid past themselves in the bore. Hence the piston will slowly move though the fluid / bore but none will actually be lost anywhere.

But wouldn't that cause the pedal to creep all the way to the floor?

[BazaJT]

I'll follow this with interest as last time I drove mine I too thought the pedal rather too close to the floor for my comfort,but similar to TB I didn't know if it was just due to being used to the pedal "feel" of the V70.If it should be the master cylinder seals are seal kits available?Or is it case of swapping the whole thing?

[Andy H]

It still sounds like the master cylinder to me .if there are no other leaks and the fluid does not go down.( you could clamp the front hoses first and then do the rears if you have only two clamps !) to do the previous check.The master cylinder can fail in two ways.either fluid leaks out of the back and into the servo but this would cause the level to drop or it can leak internally.ie the seals leak fluid past themselves in the bore. Hence the piston will slowly move though the fluid / bore but none will actually be lost anywhere.

But wouldn't that cause the pedal to creep all the way to the floor?

Only if the seals are completely shagged.

Most of the time the brake master piston spends it's time working over a short range in the cylinder - once that bit of cylinder has become worn and scored the  piston has to travel a bit further down the cylinder before it achieves a leak free seal.

Fitting new seals would improve things a little but it wouldn't remove the scoring (which is why you are meant to hone the master cylinder before changing the seals).

+1 for new master cylinder.........

[Kevin Wood]

Mine creeeps a little too, and only with the servo assistance. I think this is because you can generate way more pressure via the servo than you can manually. There is no more "give" in the servo than directly via the pedal, so it's the master cylinder piston dropping regardless of anything else.

It's clearly not any of the 4 wheel cylinders as they would be leaking. Could be a tired master cylinder seal, and it can potentially be an MOT failure. I wondered if mine would be OK at MOT but didn't get a comment, so clearly not bad enough yet.

Haven't tried playing with Tech 2 on the ABS unit. Might give that a go and see if mine is the same as yours next time I CBA.

[Doctor Gollum]

Any sign of brake fluid in the vacuum line from the servo?

[ajsphead]

Had exactly the same problem with a previous Omega. Checked in the same way, changed master cylinder, made no difference. Current Omega did the same thing, stripped and rebuilt front calipers on advice from my friendly mechanic and got the best Omega brake pedal I have ever had. Two years later and it's back to mush again, fluid change made no difference so am considering whether rebuilding the rear calipers might help too. Free movement on the slide pins seemed to be the issue.

[terry paget]

Had exactly the same problem with a previous Omega. Checked in the same way, changed master cylinder, made no difference. Current Omega did the same thing, stripped and rebuilt front calipers on advice from my friendly mechanic and got the best Omega brake pedal I have ever had. Two years later and it's back to mush again, fluid change made no difference so am considering whether rebuilding the rear calipers might help too. Free movement on the slide pins seemed to be the issue.

Makes sense. I have had front slide pins seize solid, and rear pistons seize solid. Cured both by replacing calipers. I suppose we should expect these things in 17 year old cars, with brake pads changed rarely. I recall Quentin Wilson's interview with the police garage mechanic about his 24 valve Senators, being told 'we change the brake pads every fortnight and the tyres once a month; nothing else on thse cars goes wrong'. I doubt they had trouble with seizing pins or pistons.