22 replies to this topic

[Staddon]

MoT place have said that when the brake pedal is pressed, the rear brakes will brake much more than the fronts and almost lock up before the fronts start working.

[ibrooks]

OK so the MOT station has measured a brake imbalance - too much rear braking effort.

 

There can be two reasons. Either the front brakes are providing low effort whilst the rears are OK or the proportioning valve is dud and not limiting the pressure allowed to the rears as it should.

 

The fronts being low should be obvious from their readings but what worries me is that the testing station have specifically mentioned a device that the Mini doesn't have. It suggests a level of incompetence on their part or that they are being devious hoping to get work by baffling you with terminology. It makes me question whether they can be trusted to spot where the problem really lies from the readings on their equipment or whether they can be trusted to tell you if it's something simple like possibly sticking pads rather than the proportioning valve needing replacing at not inconsiderable cost.

 

I'm guessing this place doesn't do much testing on older cars. Much as it can be painful to write off the test fee already paid it might be worth taking it somewhere that knows older cars and having it tested again to get a more accurate diagnosis of where/what the actual problem is.

 

Iain

[Staddon]

Don't worry, they're not carrying out the work, a friend of my dads a mechanic, who's owned about 5 minis and myself are doing it.

You know what? I think I will take it to some other place as even after ringing up, the guy wasn't sure what the problem was. They had just put it down to the valve (the one a mini doesn't have) and he then went on to simply describe the problem and quite a number of parts which may be causing it..

[Ethel]

I'm dubious about the MoT tester's diagnosis. Does he have a 4 wheel brake tester? If not how is he comparing the brake effort on two separate tests? Even then, how has he identified the proportioning valve as the fault, and not anything else degrading brake performance at the front?

 

Which pattern master cylinder do you have? Is there a plastic ID band round it, are the pipe unions the same size? Also, look at the condition of your discs and pads; remove the pads to check the pistons aren't seized.

[Staddon]

Can't check right now as I'm away from home for next week, but will do all that when back.

Thanks for your help though guys!

[firstforward]

To tell if the rear brakes are overbraking you do not need to even test the front brake performance. When the rear brakes are tested on the rollers if they lock up on pedal application that is enough for a fail - period. Of course the problem will be exacerbated on the road if the front brakes are underperforming.

 

Admittedely the tester has used the wrong description on possible parts required but that is another story.

[Ethel]

I've had plenty of MoT's where testing rear brake performance on a Min has been a tad "challenging" as it climbed off the rollers before reaching the required figure. Weighing it down with a mechanic or two was needed.

 

If it did lock up with minimum pedal effort, I'd be looking at the brake shoes and pull off springs: not the valve.

[firstforward]

Yes I agree that can happen but usually with a handbrake test it climbs the rollers, on footrake the front brakes are holding in place. I have had a drum out of true that locked up the rear on one side so maybe there is more to the MOT testers diagnosis than we know, if it was on both wheels that could be why but until inspection is carried out we shall not know.

 

A simple brake test on a safe road will tell if it is both or just one side that locks up. If it is one side go with Ethel's suggestion.