Rear brake cylinder size
Turbo Mini Forums

Currently ive got 7.5" disc on the front, single line system with standard 0.7" master cylinder, regulator valve mounted to the subframe. The braking is crap, i plan to overall the rear brakes, what size rear brake cylinder should i use. Also is it worth fitting a brake bias proportion valve?

Chris

1972 998 TURBO SLEEPER

Bin the factory regulator, fit a bias valve instead.

What’s crap about the brakes?

stopping power, fade and pedal travel is fine once bled, but fades fairly quickly.

1972 998 TURBO SLEEPER

You still using the standard drum brake pedal ? If so I had the same problem fixed it by fitting a later disc brake pedal.

Yes, does the disc pedal have a different ratio?

1972 998 TURBO SLEEPER

Put some good pads in the front, Mintex 1144 or Ferodo DS2500. They will transform the brakes. I had CooperS brakes years ago and they were great.

If your original is the earlier square pedal, as mine was.

Cheers Tom

It’s a 1972 pedal box

1972 998 TURBO SLEEPER

Most braking is done on the front so if its as bad as you say, you really need to look at the front brakes first. If you have a problem locking the rear brakes, then you need to look at increasing the bias more towards the front.

If you fit an adjustable bias valve, fit any of the smaller rear wheel cylinders, other than the more common 3/4" ones. This will give you more control over the bias. 1/2" is as small as you can go on the rear, and were fitted on only a few early models without any pressure reducing valve. all later cars used the 3/4" wheel cylinders with one or another type of pressure reducing valve.

as for the brake pedal, the lever ratio is exactly the same, only difference was the reserve pedal travel when they changed from a single line master cylinder to a dual line master cylinder, you have to stomp on the brakes equally as hard on either pedal, just that one pedal position is higher up than the other.

I agree with Tom, the Mintex 1144's or similar. What pads are fitted?

Oh, and if you want to know what the car should have fitted as standard, have a look on Minispares, they have a chart the explains all

Edited by Sprocket on 4th Apr, 2018.

Sorry colin but I went though all this, only the later hexagonal pedals are the same.
If longy has square pedals this will be the problem.
Mine passed it's mot with the drum braked pedal and where ok around town taking it easy. Once you started to push a bit, the brakes where crap. I changed the pads, the fluid even though it was new in fact everything was new.
I think one of the problems is with the fluid return, the drum pedal not allowing enough fluid back to the cylinder. Effectively pumping the rear brakes up which eventually stops the front been applied fully.
One one occasion the rear drums had actually started to lock up and the only way to release them to drive home was to open the bleed valve on both rear cylinders to let the pressure off.
All this is single circuit on a 1970 mini with full S brake set up.
The way I fixed it was to fit a brake pedal from a '86 mini.

Thanks for the feedback guys,

Colin the pads currently on there are Mintex GBP103MIN, ill get some 1144's.

I there is definitely too much bias towars the rear as i can lock up the rears. All in all apart from the front discs/calipers/pads the system in tired and needs overhauling.

Just found this thread on the mini forum,
http://www.theminiforum.co.uk/forums/topic...ni-brake-pedal/

1972 998 TURBO SLEEPER

Which shows that the pedal ratio is still the same but the pedal is just higher up

So are you saying theres no operating difference between older pedals/newer pedals/servo pedals?