21 replies to this topic

[Haydns]

Hi,
I'm new to mini's but have spent many years working on mg's and austin healeys.

I now have a 2000 reg mini 40. (cooper) which is in good nick but has failed its mot due to the rear brakes not locking up. I've gone through the system, changed the shoes bleed out the old fluid all round but still have the same problem. The handbrake locks solid on 3 clicks so the rears are adjusted properly, and all looks well when bleeding them, pedal has a good solid feel so I'm a bit stumped!

Any advice gratefully received.

Regards
H

[Carlos W]

What does the fail sheet say?

The rears shouldn't lock up should they?

[Ryang556]

What does the fail sheet say?

The rears shouldn't lock up should they?

I was thinking exactly this

[bmcecosse]

The rears don't need to lock up - they do need to provide braking forces! Probably the cylinders are seized and the linkages inside will be seized up too. A complete overhaul costs pennies (well - not much anyway) in parts. Just DO it! But as above - what does the sheet say ? Did it fail on both foot and emergency brake ??

[Haydns]

Hi!

The sheet says. RBT service brake efficiency 41%. Spoke to the tester and he said the fronts were fine and the problem was with the rears. Parking brake is working normally.

The rear cylinders looked ok from a visual inspection. But with someone pressing the pedal hard I can rotate the rear wheels with reasonable effort (two hands on the wheel and a firm turn).

If there are no obvious tricks that I'm missing then I guess it's a new set of rear cylinders?

Cheers
H

[Ryang556]

I'd say it's defiantly a new pair of rear wheel cylinders, probably seized

[Carlos W]

Could be seized adjusters!

Have you tried adjusting them?

[Haydns]

Hi Carlos,

Yes I've adjusted them up and the hand brake is solid on 3 clicks so it's not that, must be the cylinders?

Cheers
Haydn

[Carlos W]

Or a faulty bias valve??? but I know nothing about this, so hopefully someone who knows what they are talking about will come along soon!

[Haydns]

Could it be the pressure reducing valve? Both rears seam to require the same amount of force to rotate then when the pedal is being pressed hard down, suggesting its a common issue to both ( which could still be the wheel cylinders).

H

[Cooperman]

The rears should never lock up, even with the pedal pushed down very hard, but they should meet the MoT requirements. Does your MoT tester realise this?
However, if both sides fall way short, then it could well be the pressure relief valve or, possibly, both the rear cylinders.

[bmcecosse]

Possible someone has fitted small bore cylinders - and the pressure from the bias valve is just not enough to do the job...... I much prefer to dump the ghastly bias valve - and fit the old style pressure limiting valve - which can then be fine tuned to get good rear brakes without risk of locking. Someone recently put up a link to what seemed a very reasonably priced adjustable bias valve......I think from Wilwood. So - if the rear cylinders/links etc are found to be NOT seized - that may be a way to go.

[Ethel]

It could also be a faulty master cylinder. I assume it's a horizontal servo master? You could familiarise yourself with the actual MoT requirements, maybe the handbrake passes because it doesn't need to show as high a brake force as the foot brake - even though there's a common fault?

Knew I wouldn't be able to resist reading up on the specifics of the test,

There is no rear brake performance requirement.

You just need 50% overall service brake efficiency, with the front brakes being within 25% of each other.

The handbrake needs 16% efficiency, 25% on cars with a single brake circuit.

This also means you can't pass on the front & fail on the rear. I also thought the brake rollers' results were now fed straight into the VOSA computer terminal.

[Jordie]

the brake rollers arent directly linked, the tester has to input the readings and click the "locked" box on the page before giving the result (pass / fail)

[lrostoke]

I would try the following

Adjust the rear shoes until the wheel locks up, then back the adjuster back a quarter turn.

Although actually I've noticed on mine and a couple of other I can turn the rear wheels using reasonable force with the footbrake applied.