Stupid Brakes... Mot Fail Again

[davey sprocket 14]

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.

 

 

Hmm... you know, I do agree with you... and I'm wrong to blame the guys at the test station. And I'm certainly not expecting them to falsify any readings.

 

But....

 

What else can it be??

 

Like Welshpug said, some test stations don't have state of the art rollers that do it all for them and print out pass or fail, they actually do it manually and make a decision themselves.

 

Brake pads don't go off do they?? there's plenty of life in them. The discs are absolutely fine.

 

We know the rears are capable of plenty high enough readings from when I had the faulty compensator in the line. Good compensators are limiting the rear brake effort to 40-50 whatever it is units on their machine.

 

I've passed the 10 days where I can get the car back in for a partial retest, so I'll have to have a full test now anyway. I'd rather do so somewhere else.

 

Should I throw new pads in the back tonight???

I'll re-bleed the rears again in case I've not got all the air out from changing the compensators.

[welshpug 1,683]

given the handbrake gave good readings id imagine the pads are fine

[C_W 3 1 Cars]

My experience is even with nice condition calipers, good pads and discs, they do the best part of FA. The only time my rear discs were ever not rusty was after very hard use on track - under normal driving they always tended to be half rust/half metal lol.

 

I could tell mine weren't used heavily as often the discs looked in ok condition, but actually the disc is quite rusty and you can literally chip plenty of it off with a hammer as it's actually rusty underneath but the top surface looks ok as it's been polished by the pad!

[Miles 331 1 Cars]

I could make up a bypass for the comp valves if it came to it, I know using a bias's valve on some of my cars the rears really do work

[davey sprocket 14]

Cheers Miles,

 

As I suggested above, I took the car elsewhere and she went straight through the test with another station, not even an advisory.

 

The first station I used was unbeleivably picky, like I said to you when I brought her over... had advisories on oil leaks (which were fixed ages ago and there is just some residual left over) and all sorts including the tiny chip in the windscreen that was there when I got the car and two other test centers have ignored.

 

The offside compensator was clearly faulty as replacing that with the one from the other side evened them up lovely. I do still suspect that the rears are underperforming somewhat but I'm sure that's how they've been for the 3 years I've had the car. The car stops fantastically well. There isn't much else to replace that could improve the standard performance.

 

I'm sure an adjustable bias set up is the way to get the absolute max out of the standard brakes, it's a shame you can't get an adjustable compensator valve to replace the standard ones as you could tune it to perfection.