18 replies to this topic

[emalee]

Model: Mini Sky
Year: 1989
Description of problem :

My brakes have progressivly got worse over the past month and the rear brakes lock up very easily in anything more than normal braking.

90% of the braking system was renewed in May including all the brake pipes are either new copper ones, or stainless flexi hoses,the calipers have been rebuilt with stainless pistons with green stuff pads and new discs, and the rears are new drums, shoes and cyclinders. and the rears are fully adjusted up and the drums cleared of any build up of dust. The brakes used to be perfect on it untill a months ago

The Front brakes just don't seem to be getting enough power to them to stop!! and instead the rears just locking

We've bled the brakes tonight and all was well and it hasn't lost any fuild

the only other thing with the brakes it that during the summer the brake pedal sticks down, and when we were bleeding the fronts it was sticking down again

has anyone any ideas of what it causing it?

Thanks Emma

[Surfbluegarage]

not 100% on this but wld connecting the compensater valve up wrong do anythin to cause this??

[bmcecosse]

Possibly the front pads have 'glazed' - and are now not working as well as before - at normal temperatures. The brake balance seems to be too much to the rear (very dangerous! Easy to spin!!) - the answer is to fit smaller diameter rear brake cylinders which will reduce the braking effort at the rear - for the same pedal pressure.. do you happen to know what size cylinders were fitted at the overhaul ?

[bmcecosse]

Yes - the compensator valve wrong way round would do this - when I got my last Mini that's EXACTLY what the bozo who had it before me had done - the braking was terrible - and it would spin in a minute - and it had a brand new MOT!! However - poster says the brakes worked ok before - so I think it's something that has deteriorated.

[Surfbluegarage]

yeah just a thought as he said hed overhauled it and possibally cld have made new copper pipes up the wrong way round from the master???
would it do it from the off rather than just go then if it was the wrong way round?

Edited by mini_mad_daps, 18 January 2010 - 09:43 PM.

[emalee]

Possibly the front pads have 'glazed' - and are now not working as well as before - at normal temperatures. The brake balance seems to be too much to the rear (very dangerous! Easy to spin!!) - the answer is to fit smaller diameter rear brake cylinders which will reduce the braking effort at the rear - for the same pedal pressure.. do you happen to know what size cylinders were fitted at the overhaul ?

i'm not too sure which cyclinders they were - but they were brought from my local mini specialist for that car so they should be fine, its just odd that the brakes have been fine for 6-7 months and have just started playing up!!. I also have exactly the same set up on my other mini which is fine for the temperature etc...

could it be the bias valve playing up sending too much pressure to the rear rather than the front??

[bmcecosse]

Best way round it all is to ditch the ghastly 'compensator' - plumb the front brakes direct - and put an old style 'pressure regulator' valve in the feed to the rear brakes. The spring in the PR can then be adjusted to get just the right amount of rear braking - even with large bore cylinders.

[emalee]

Yes - the compensator valve wrong way round would do this - when I got my last Mini that's EXACTLY what the bozo who had it before me had done - the braking was terrible - and it would spin in a minute - and it had a brand new MOT!! However - poster says the brakes worked ok before - so I think it's something that has deteriorated.

the brakes were fine for months, and i was very careful when putting it back together and double checking against my other mini to make sure it was all connected up right

[bmcecosse]

Yes - the fact they were fine for months does suggest the problem lies with the front brakes - does it lock the front wheels on a dry road ?

[emalee]

Yes - the fact they were fine for months does suggest the problem lies with the front brakes - does it lock the front wheels on a dry road ?

No!!, just the rears!!

[bmcecosse]

Ah well - but did it used to be able to lock the fronts ? Mini brakes MUST be able to lock the front wheels on a dry road (at 30 mph) .

[emalee]

this is how the Bias Valve is plumbed in - i know its bolted in the wrong way, but i pretty sure the hoses all go in the right way!!

[emalee]

Ah well - but did it used to be able to lock the fronts ? Mini brakes MUST be able to lock the front wheels on a dry road (at 30 mph) .

Yeah they used to lock all 4's when we were frist testing the brakes!!! I know i need to sort them as soon as possible!!

[bmcecosse]

Well - I suggest an urgent new set of front pads - just use standard material - but it should NOT be able to lock the rears. I solved it by fitting the pressure reg valve and ditching the so called 'compensator' - it's MUCH better!

[emalee]

Well - I suggest an urgent new set of front pads - just use standard material - but it should NOT be able to lock the rears. I solved it by fitting the pressure reg valve and ditching the so called 'compensator' - it's MUCH better!

I will look into the pads as we haven't checked them since the rebuild and its done about 8k on them, i think i have a spare standard set some where!!