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[Doctor Gollum]

Would it be possible to reconnect the brake lines in the wrong ports on the ABS block?

What effect would that have?

[Nick W]

Would it be possible to reconnect the brake lines in the wrong ports on the ABS block?

What effect would that have?

It's hard enough connecting them correctly.

[cam.in.head]

Yep, if the MOT brake tester shows an imbalance then it's clearly not down to the bushes. That doesn't mean they are OK, of course.

I can't remember how the brake circuits are split on an Omega. A problem anywhere other than the caliper would affect both sides equally if they're on the same circuit, which I think they are.

Thanks for that.  Its beginning to seem like I might as well start by looking at the caliper and either replace or overhaul it.

Just make 100% sure that the piston retracts into the caliper as easily as the other caliper.and also peel back the piston dust cover if you can to make sure it’s dry inside, a small leak here can cause a small amount of air to be drawn back into the caliper as well.it could be hoses as you have previously thought but it’s rare and the tester would have felt them under pressure anyway.

[Greenbay packer]

Just make 100% sure that the piston retracts into the caliper as easily as the other caliper.and also peel back the piston dust cover if you can to make sure it’s dry inside, a small leak here can cause a small amount of air to be drawn back into the caliper as well.it could be hoses as you have previously thought but it’s rare and the tester would have felt them under pressure anyway.
[/quote]

Thanks, its definitely bone dry inside the boot but I think I'll do as you suggest and have a look at the other caliper too just to see if one side is moving more freely than the other. I'm guessing/ hoping the callipers are fairly easy to rebuild if the correct seal kit and/ or new piston is available.

[cam.in.head]

Yes ,dead easy,especially as it’s only a single piston type.to be honest though if the inside of the boot is dry and the piston not rusty and you can push it back nice and easy you won’t achieve much by rebuilding it the usual cause of imbalance on these is the two slider pins/bolts but you have already checked them. The way to get balanced readings(within tolerances) is to have equal physical properties each side.this means identical pad composition,disc condition,caliper condition,hose condition and all new fluid.you will never get a balance of absolute zero but one side coming on before the other USUALLY means that the faulty side has an issue somewhere.nothing to do with anything on the suspension ,bushes,tyres ,etc as the brake rollers are only measuring the effect of what it sees the brakes doing.
Have you got a good pedal!. If not you could still have an air bubble somewhere on that side in either the pipes,abs unit or caliper .

[Greenbay packer]

Yes ,dead easy,especially as it’s only a single piston type.to be honest though if the inside of the boot is dry and the piston not rusty and you can push it back nice and easy you won’t achieve much by rebuilding it the usual cause of imbalance on these is the two slider pins/bolts but you have already checked them. The way to get balanced readings(within tolerances) is to have equal physical properties each side.this means identical pad composition,disc condition,caliper condition,hose condition and all new fluid.you will never get a balance of absolute zero but one side coming on before the other USUALLY means that the faulty side has an issue somewhere.nothing to do with anything on the suspension ,bushes,tyres ,etc as the brake rollers are only measuring the effect of what it sees the brakes doing.
Have you got a good pedal!. If not you could still have an air bubble somewhere on that side in either the pipes,abs unit or caliper .

Thanks for the reply, its confirmed what I was thinking particularly with being able to rule out things like suspension, tyres, etc, which is a big help. The pedal is good and firm and its position doesn't change when I pump it. I was hoping there may still have been some air somewhere and that the rebleed I've just done would help but it doesn't seem to have made any difference. I might try pumping the piston out a bit further as I've only seen about 1/2" of it so it may be in worse condition further inside the caliper. The problem only seemed to arise after I'd changed the discs and pads and the caliper piston was pushed right in to take the new pads. I've actually been contemplating putting the worn pads back in briefly just to see if there is any difference with the piston operating further out of the caliper bore but I know that's a poor idea as the old pads will be worn differently.

[BazaJT]

If you're going to pump the piston out a bit further you'll need to put the old pads in first anyway.Whatever you do don't try pumping the piston out with nothing in the way to stop it coming out altogether.

[Greenbay packer]

If you're going to pump the piston out a bit further you'll need to put the old pads in first anyway.Whatever you do don't try pumping the piston out with nothing in the way to stop it coming out altogether.

 

[terry paget]

I have driven cars with rod brakes, and cable brakes; they were all right, both had some method of compensation to achieve left right balance; it worked, often with a slight delay, causing a steering twitch as it settled down. The way you describe your fault, it sounds similar; an initial twitch one way, settling down with both sides braking evenly.
If that is the case, I don't think you should exclude suspension behaviour from possible causes. If both front wheels showed the same retardation rate after a small delay, my money is still on wishbone front bushes. With the car on a rolling road testing rig, the car does not move, but if left and right suspensions respond differently as the brakes are applied, this will appear on the testing system as a delay.

[cam.in.head]

Hi terry if you were testing "on the road " i would agree with you 100%. Omega front suspensions are very sensitive to bushes wear and if any one was worn then they do have that strange feeling of brake pull one way and steering wheel twitch the other but i assume these brakes here were tested on rollers and one brake operates before the other does.this can surely mean that the slower side to operate has either a small air bubble still in it somewhere or a small leak in a piston seal drawing air in when pedal released.or a stiffer piston on this side,(he has confirmed that hes got matching discs,pads and checked slider pins).
My money is on a stiffer piston or air bubble.

[terry paget]

Hi terry if you were testing "on the road " i would agree with you 100%. Omega front suspensions are very sensitive to bushes wear and if any one was worn then they do have that strange feeling of brake pull one way and steering wheel twitch the other but i assume these brakes here were tested on rollers and one brake operates before the other does.this can surely mean that the slower side to operate has either a small air bubble still in it somewhere or a small leak in a piston seal drawing air in when pedal released.or a stiffer piston on this side,(he has confirmed that hes got matching discs,pads and checked slider pins).
My money is on a stiffer piston or air bubble.

The whole point of hydraulic brakes is that all brakes get the same pressure simultaneously. That holds even when there is a bulgy hose or air in a cylinder. The rolling road brake tester presumably measures the resistance by the braked wheel to roller rotation. Roller speed is very slow, so if initially a braked front wheel can move backwards that will appear on the tester as a braking delay.

[dave the builder]

when on the RBT
if the caliper was sticking ,the drag/bind would register
 you run up to centralize the wheels, you select which wheel to spin up
then once the roller is up to speed, the brake should be depressed gradually ,increasing to full braking or lock
then reduced gradually

Better still ,watch the MOT Matters video on brake testing
https://www.youtube.com/watch?v=xVpgCKz8oWs
but the VTS device works out the in-balance now IIRC 

I know some mot testers get it wrong

also well worth watching the MOT mistakes
(which some MOT testers should watch too ,from past experience )
https://www.youtube.com/watch?v=MT8ZbRvemhg

[terry paget]

Thanks Dave. I enjoyed those testers' guides enormously, and learned a lot from them.
The OP had a steering pull last year's MOT, tester failed the car. After some fiddling OP improved matters slightly and car just passed on retest. Car still has a steering pull and is soon due for test again. Car is 22 years old, and must have had wishbones changed. Do you know when they were last changed, Greenbay Packer? Was a new pair fitted, or just one? What make were they? As I said in post 9 of this thread, it was very obvious to me mine were faulty, watching from below as car above me braked. Without a pit its hard to imagine a simple test. Perhaps you could lever both front bushes in turn with front of the car on axle stands.

[dave the builder]

had a caliper with a problematic piston before , very odd
kept sticking , worked it in and out and all was fine for a week or so , then the same again
I'd inspected it ,no rust etc
I replaced it with a known good used item
examined the dud unit with digital micrometer
the piston had gone "out of round"
which if you think about it ,can happen because the piston does get dragged in one direction by it's pad and calipers all the time during braking, not much but enough to cause the issue

If it was my car (or one i look after) I would buy a used replacement caliper(would be cheap and easy to get hold of) i
present for mot early , if there is an in-balance issue  then you have the spare ready to go on
but you can't rule out other issues like a dud ,semi jammed/part blocked  solenoid in the ABS module etc
IF all the slides / pads/ discs  / fluid /wheel bearing  etc is ok (including manufacturing faults so compare o/s and n/s for any slight size differences etc)
and you've checked the suspension components both sides
(it could be a duff component on on the non pulling side that makes the car pull to the problem side )

also, familiarize yourself with the RBT procedure as per the video and watch them do the test if possible 

not that i'm saying your garage is one of the bad ones , it does sound like you have an issue

I just don't trust garages

I'm fortunate to have an MOT tester that is strict but fair

I've missed things in the past ,he has too , we are all human
 (though Mrs Builder may argue that point about me  )

[dave the builder]

having re-read the first bit of thread and thinking 
maybe the n/s lazy caliper is fine and the other side driver's ? is sticking and bites sooner
so worth getting both as free as possible