Stupid Brakes... Mot Fail Again

[davey sprocket 14]

Background:

Last two MOTs and this current one, have had advisories for all flexi hoses slightly perished and brake lines corroded.

Failed MOT this time on rear brake balance, N/S low effort. Went to give rear brakes an overhaul but both rear bleed nipples sheared off. Bugger.

Decided to bite the bullet, get the car up to Miles for the whole lot replaced. Near new master cylinder that I already had, new front pads, all new flexis, copper lines right through, one recently reconned rear caliper and one good second hand.

Fantastic.

 

Took car back for retest today.... rear brakes exactly the same as before. Tester called me in to have a look... on footbrake operation O/S pulls about 145, N/S 40-ish. Handbrake not too bad, about 120 each side.

 

Now the only thing that is the same on that part of the circuit as before the work is the compensator. Is my reasoning right??? I assume if one compensator is playing up, that side will be down on braking, or is it the opposite side??

Do GSF carry the compensators? Can't get onto their website from work.

Edited June 20, 2011 by davey sprocket

[Anthony 1,003]

If it's a 1.9 GTi then it'll almost certainly be a compensator issue in my experience, especially if the handbrake is OK.

 

I'd personally go with the low reading one being at fault if you're not locking a rear wheel under heavy braking, although to be honest unless money is tight I'd replace them both for peace of mind and so that you've got a matched pair.

[davey sprocket 14]

Thanks Anthony, yes it is a 1.9. Miles said the rears both seemed to bleed OK, so we didn't expect any further issues.

 

What are these compensators?? A pressure limiting valve of some sort presumably?

 

I also need to figure out if I can get hold of them kinda sharpish. I think GSF will still be open after I get out of work but don't know if they do them let alone have them on the shelf.

 

'Suppose replacing one or two comes down to how much they are!

[feb 47]

A few years ago I had both of these replaced in my 1.9 (within a month of doing one I did the other) to cure a rear wheel locking issue under heavy braking.

I can't remember exactly how much they cost but they weren't cheap (70 pound odd IIRC?).

Edited June 20, 2011 by feb

[Anthony 1,003]

1.9 compensators are pressure limiting valves as you say, and there's valves out there with differing pressures, hence the comment about a matched pair ideally.

 

They normally seem to fail either fully closed (ie little or no effort, barely any fluid passes trying to bleed) or fully open (ie excessive effort, easy to lock the rear wheel) but I guess they must have a failure mode that allowed them to give low effort. Certainly 40 sounds distinctly low if you're getting 120 ish on the (notoriously crap) handbrake. Fronts probably would have been 200-250 ish I guess if you've got the brake roller printout in front of you?

 

GSF certainly used to do them, although no idea if they still do thanks to their stupid website rehash - they used to be about £30-40 each from memory.

 

I think that I've got a couple of newish looking ones around somewhere if you get stuck.

[davey sprocket 14]

Thanks both.

 

I just can't think that it can be anything else... what are the chances of replacing so much of the system and having exactly the same defect as before?

 

As this was a retest they didn't re-do the fronts as they passed the test first time, so I don't know what the readings were like up front.

 

I'll stop by at GSF on way home.

 

Kind offer Anthony, problem is I've got 10 days from the original test date (which was last Monday) or else its another full re-test, so kinda short on time.

[davey sprocket 14]

GSF do have them (well one) on the shelf. £46 inc VAT.

 

Have had a bite to eat and now trying to find some enthusiasm to go out in the rain to fit it and re-bleed the brakes.

 

Wish me luck.

[davey sprocket 14]

OK, so that wasnt too bad because it's only been together a few days.... and why did I wait all these years to invest in an Ezebleed kit??

 

 

I guess I'll find out on the MOT station's rollers tomorrow whether that has made any difference. Having been up and down the road, leaping on the brakes, the rear discs both feel plenty hot enough (ouch!) to suggest they're working.

Edited June 20, 2011 by davey sprocket

[TT205 42]

Fingers crossed

[davey sprocket 14]

FFS

 

OK, I'm fed up now. Will take the afternoon to decide whether just to park the car up for a while or to try and figure out what could actually be wrong here.

[welshpug 1,682]

just fit a pair of compensators

[davey sprocket 14]

Am I missing something along the way???

 

Between the pedal and the wheel there are:

 

Master cylinder (changed for known good used one)

Solid brake lines (all replaced with new copper)

Compensators (one on the side that is reading low has been replaced with brand new genuine Bosch one)

Flexi hoses (all replaced with new)

Calipers (both rears replaced with good used parts. The caliper on the problem side is like new, recently refurbished)

Discs and pads.

 

Now, I've discounted the discs and pads as they look fine and the handbrake works as well as they ever do and doesn't seem to read low on the problem side.

How does the handbrake actuate the brake?? Does that mechanical actuation push on the pads independently of the hydraulics or does it push on the hydraulic piston?

Could the pads be crap but the handbrake is making them work somehow but the hydraulics can't??

 

I'd understand this if there was any difference whatso-ever from how it was to start with, better or worse but nothing seems to make any difference at all!

[davey sprocket 14]

just fit a pair of compensators

 

How can the compensator on the off side reduce the effectiveness of the brake on the near side??

 

Having replaced the nearside one with new and it making not the slightest difference, there was clearly nothing wrong with it. I might fit that to the other side, see if that makes any difference.

Edited June 21, 2011 by davey sprocket

[TT205 42]

Why not pay Miles a visit before you attack it with a tree branch! - he's only in Ringwood

[davey sprocket 14]

Why not pay Miles a visit before you attack it with a tree branch! - he's only in Ringwood

PM'd

[welshpug 1,682]

Thats certainly the approach I'd take with the compensators, thay can seize wide open as well as shut.

[feb 47]

I might have followed the same approach a few years back when one of my rears was locking up, replcaed the same side compensator which had no effect and then had to replace the other one as well.

It doesn't make sense to me either but worth replacing the other one as well as others have said.

[C_W 3 1 Cars]

How can the compensator on the off side reduce the effectiveness of the brake on the near side??

 

Having replaced the nearside one with new and it making not the slightest difference, there was clearly nothing wrong with it. I might fit that to the other side, see if that makes any difference.

 

 

My opinion is that your attention is on the wrong side; it's the one with more braking power that is at fault.

 

I would go with your last suggestion and put your old one that is now off the car on the other side. This happened to mine a couple of times and the first time had me chasing the lower effort caliper as the faulty one when it was in fact the other side; the main thing with the rear brakes is that they are balanced, they don't do a lot but when they're unbalanced they can really destabilise the car under braking from high speed. IME the compensators have always broke in the more "open" position which gives a high effort reading. Now if you got two "faulty" open compensators that would work too!!

[davey sprocket 14]

Right, well I'll go with the consensus then and try the other side!

 

If that does indeed bring the effort down on the off side and the MOT tester doesn't like that ( I did ask that specific question... are they sure it's this one that's low and not the other one that's high), I'll book her in at another station for a full retest.

[C_W 3 1 Cars]

I think to be fair to the tester, when you see both brakes on a brake test and one is showing as low effort then you usually think that's the one at fault. Hopefully swapping the compensator on that other side solves the inbalance!

[woodymi16 24 2 Cars]

If you swap the compensators over and the problem stays on the same side, you know its not that.

 

I had a similar problem on my 1.9 and it was the master cylinder, maybe you've been really unlucky and your replacement is faulty as well.

 

Best of luck.

[davey sprocket 14]

Rear brake balance now spot on, thank you all for your help on this! As you guys suggested, it wasn't that the nearside was low but the offside compensator had failed open and was overbraking that side.

 

Effiin morons at the test station still won't let it pass because of low effort on the rears. ......'puter says no!

 

 

Spoke to the guys in my local garage and they said they've had all sorts of problems with this test station trying to get cars through and they won't use them at all.

Car now booked in for full MOT through them at another test station, who apparently employ humans!

[welshpug 1,682]

low effort? press that pedal harder

 

not sure what the specific numbers should be for these cars, not had a printout for some time as the place I usually use has an old machine!

[Anthony 1,003]

Effiin morons at the test station still won't let it pass because of low effort on the rears. ......'puter says no!

To be fair, the brake efficiency test is quite straightforward and must achieve a minimum of a given % of the cars test weight.

 

From memory it's 50% (total) on the service (foot) brake and 16% on the parking (hand) brake.

 

Assuming that they've got the test weight correct, if putting the figures into the MOT computer says that it's failed, then I'm not sure what you expect them to do? Falsify the figures to allow it to pass? I have my grievances with certain testers either not doing their job correctly or being anal to the point that an example of that model fresh off the production line would have failed (205 headlights being "insecure" is always a favourite!) but if the brakes aren't upto scratch then they're not upto scratch!

 

Assuming the figures you're getting are comparable to the test station I normally use, 40(kgf I assume) is distinctly on the low side for the rear brakes, and is why I incorrectly assumed that side had the faulty compensator. I'd have to have a look through the paperwork to see if I've ever been given a printout of the brake test results, but if memory serves me right I tend to see around 100-120kgf on the rears and 200-250kgf on the fronts.

 

Of course, I'm not quite sure *why* the rear brake effort is low on yours, given you've replaced most of it and the handbrake (which is the usual problem!) is fine.

[davey sprocket 14]

low effort? press that pedal harder

 

not sure what the specific numbers should be for these cars, not had a printout for some time as the place I usually use has an old machine!

 

I shall feel a right pillock if it fails at the other station as well!