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[terry paget]

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

It was heartening to read that MOT testers should 'pass and advise' for many minor infringements, like one rear mirror missing, only 2 washer jets clear, etc.

[dave the builder]

 It was heartening to read that MOT testers should 'pass and advise' for many minor infringements, like one rear mirror missing, only 2 washer jets clear, etc.

Or , Dis heartening to think how many MOT fails in the past should have been pass and advise or minor fault under the new system .

yep , my glass is half empty 

[cam.in.head]

When I recently took mine for test the front brakes were 12% out of balance.(within limits ) but I wasn’t happy with that. I rechecked all the pads ,replaced the front discs and re bled the system.took it back and they were still the same.rellaced front hoses ,re bled and tried again. Still the same.garage said they were fine and nothing I could do would make them 100% perfect. No cars are apparently.no signs of any pull either.
I still wanted them better so I rebuilt both calipers noticing that the lower side DID have some slight rusting on the piston ( the others were finger push,this was tighter but not in any way seized)and a SLIGHT wetness on piston.
Rebuilt,all finger push to retract now,rebled and back again.
Brakes now less than 1% out of balance.(0.7%) 229/230
So mine was definately a caliper issue. To be honest I don’t think it was the slightly stiff piston,more like the slight leak drawing a very small amount of air in on release.

[terry paget]

When I recently took mine for test the front brakes were 12% out of balance.(within limits ) but I wasn’t happy with that. I rechecked all the pads ,replaced the front discs and re bled the system.took it back and they were still the same.rellaced front hoses ,re bled and tried again. Still the same.garage said they were fine and nothing I could do would make them 100% perfect. No cars are apparently.no signs of any pull either.
I still wanted them better so I rebuilt both calipers noticing that the lower side DID have some slight rusting on the piston ( the others were finger push,this was tighter but not in any way seized)and a SLIGHT wetness on piston.
Rebuilt,all finger push to retract now,rebled and back again.
Brakes now less than 1% out of balance.(0.7%) 229/230
So mine was definately a caliper issue. To be honest I don’t think it was the slightly stiff piston,more like the slight leak drawing a very small amount of air in on release.

Were there any other symptons, apart from the MOT brake test imbalance? Like a steering twitch on initial braking? After the initial imbalance, did both brakes show the same braking force?

[cam.in.head]

Looking at his first post he did state that it pulled to the right as the left brake wasn’t as good.then by thorough checking he got it to just pass mot.so it does sound like an issue with that left caliper one way or another.i beleive that’s what he is now concentrating on.no doubt we will soon find out.as we know they are prone to the slider pins seizing but he’s done that.
My imbalance which wasn’t enough to call an imbalance apparrently was just something that I personally wanted to get to as near. 100% as I could.its on my early cav with twin piston calipers and the slight stiffness (and it was slight) or the slight leak( which I’m convinced was the actual issue)was enough once overhauled brough them back to virtually 100%.

[Greenbay packer]

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.

Thanks for the replies and sorry for the slow response - just back from holiday. I'm going to check the wishbones again as much as anything to make sure I don't have two faults at the same time - its always possible I've sorted the caliper issue, hence the improvement which got the car through the last MOT, but also have a wishbone bush starting to fail which is responsible for the slight twitch and straighten I can feel now. Not entirely sure how old the wishbones are off hand but both sides have been changed more than once. Current wishbones are Delphi, which certainly looked ok.

[Greenbay packer]

When I recently took mine for test the front brakes were 12% out of balance.(within limits ) but I wasn’t happy with that. I rechecked all the pads ,replaced the front discs and re bled the system.took it back and they were still the same.rellaced front hoses ,re bled and tried again. Still the same.garage said they were fine and nothing I could do would make them 100% perfect. No cars are apparently.no signs of any pull either.
I still wanted them better so I rebuilt both calipers noticing that the lower side DID have some slight rusting on the piston ( the others were finger push,this was tighter but not in any way seized)and a SLIGHT wetness on piston.
Rebuilt,all finger push to retract now,rebled and back again.
Brakes now less than 1% out of balance.(0.7%) 229/230
So mine was definately a caliper issue. To be honest I don’t think it was the slightly stiff piston,more like the slight leak drawing a very small amount of air in on release.

I'm going to have a look at both callipers again, this week I hope. Although both are going in and out ok I may be able to feel if one is a bit freer than the other when I push the piston back in.

[Doctor Gollum]

I wouldn't fit Delphi wishbones to a scrapped Omega for banger racing

Last one I fitted lasted less than a week. Start there

[Greenbay packer]

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  )

That is interesting. If the piston has gone slightly 'out of round' like you say it could explain why the fault seemed to appear when I changed the pads and the piston - i.e., the piston may have round in the old position for the worn pads. Also I'm going to do as you suggest and try and find another caliper to play around with - if I'm lucky I might be able to find one that has been in use recently and is still ok. I'm also going to have another look at my wishbones.

[Greenbay packer]

I wouldn't fit Delphi wishbones to a scrapped Omega for banger racing

Last one I fitted lasted less than a week. Start there

No idea they were that bad, will check them again.

[Shackeng]

I wouldn't fit Delphi wishbones to a scrapped Omega for banger racing

Last one I fitted lasted less than a week. Start there

I had the same experience with my beloved TD Estate years ago. Fitted Delphi, they lasted less than a year.

[Greenbay packer]

I wouldn't fit Delphi wishbones to a scrapped Omega for banger racing

Last one I fitted lasted less than a week. Start there

I had the same experience with my beloved TD Estate years ago. Fitted Delphi, they lasted less than a year.

Thanks for the reply.  The only reason I fitted them was that I've had a set of Delphi's on our workhorse Astra and they've been great for many years so I thought they'd be ok on the Omega too. Previous (unknown brand) set fitted to the Omega by a local garage lasted barely 18 months with very low mileage so I was hoping to improve on that.  Is there a brand that is recommended other that GM?

[Doctor Gollum]

The ATP set for £69 is about the best value available 

Currently on ebay.

[Greenbay packer]

The ATP set for £69 is about the best value available 

Currently on ebay.

Had a look just in case I need them but couldn't find on eBay.

[Shackeng]

The ATP set for £69 is about the best value available 

Currently on ebay.

Should that be All German AL?