Which rear wheel Cylinders?
Turbo Mini Forums

Hi,

Can anyone offer any advice on this please?

I've got a Mk1 (1966) with tin top master cylinder, single line brakes with regulator valve on the rear. Cooper S discs + calipers front with drums to the rear.

It's just failed the MOT on lack of brake effort at the rear. I've replaced the wheel cylinders (+shoes and drums) as they were seized. I wasn't sure what to go for and there we no refs on the them. In the end I've fitted 0.500" following some advice I found on here.

Failed again today on the same thing. To be honest I think they need bleeding again as the pedal is still not very firm but just wanted to make sure 0.500" wheel cylinders (GWC1126) are the right choice.

Any thoughts?

Thanks in advance.

Its a long time since I've done anything with rear brake wheel cylinders, but the 1/2" rear cylinders I thought were for use without the rear mounted limiter valve?

Edited by Tom Fenton on 8th Jun, 2018.

Have a look at this chart

http://www.minispares.com/catalogues/class...rt.aspx?1~9~105

I reckon a 0.625" rear cylinder is a better choice.

yed Deffo not much on the rear with the 1/2” cylinders and the limiting valve. Which valve is it though as the cooper S had a different valve rating as well.

Mine only passed the test as there’s so much brake on the front it made up for the lack of rear.

What brake force were you getting on the rear. Mine barely made 12kg per wheel

Maybe the simplest route is to remove the rear limiter valve and fit a T piece and then see how they are? Be a shame to have to remove brand new 1/2" cylinders to fit something else.

Thanks for the input so far.
I'm sure the limiter valve is a normal one rather than an s one.

He didn't give me any figures only that it's worse now that before I changed them!

Might order a new limiter valve and some 0.675 unless anyone has any better ideas.

What were on the car to begin with? If they were bigger than the 1/2” ones then that’s why it’s “worse”.

Most minis were fitted with the 3/4”. The chart Tom links to is all you need to refer to to find out what should have been in there.

Edited by Sprocket on 8th Jun, 2018.

On a side note. If the parking brake passes, but the service brake fails on the rears, it’s to do with the wheel cylinder size and limiting valve.

Thanks for the help guys

Before you spend any money did the MOT tester know what he was doing?

The MOT system won't have the expected brake efficiency for a 1960s mini, so he will need to do a calculation on the basis of axle weight.

Because there is not much weight on the rear axle, required brake efficiency is quite low, otherwise you would lock up rear wheels under hard braking.

HOSS

I use Dave Payne at Seisdon Post Office Garage for my MOTs. He has a couple of classic minis so knows what he is doing with them. If you are in bham, not a million miles away. He did the brake efficiency calculation when he tested my Elf.

HOSS

With the single circuit limiter the harder you press the brakes the less effort goes to rear brakes, to avoid lock up under hard braking, Dave was able to demonstrate this on the MOT brake tester, again a lot of testers don't understand how old car brake systems work, they are used to modern cars with ABS etc.

Maybe why 40+ year old cars no longer require MOT.

HOSS