Rear Wheel Cylinders

[PJ]

One rear wheel cylinder started leeking badly over the weekend and needs replacing. It appears that over the models/years minis have used at least 5 different diameter cylinders. I've just stripped mine out and measured it as 19.0mm but it's obviously not the original 1981 part and I cannot be 100% certain that it is a correct replacement. My suspicions are further aroused by the holes in the backplate for the roll-pin: there is one infront of and one behind the bleed nipple, on the same level as the nipple, but the forward hole has another hole immediately above it breaking into it like a figure 8. The only picture I can find of a backplate (Minisport catalogue) shows a single hole in front of and level with the nipple hole. It all suggests to me that mine has been bodged at sometime to take a different wheel cylinder. The cylinder on there now has a roll-pin that goes through the forward, lower (in line with the nipple) hole.

So, does ayone know:
a) were the roll pins in different places on different sized cylinders to ensure the correct size would be fitted.
b) what size should I have on a 1981, 1275 Californian with 8.4" discs and standard twin piston iron calipers. Master cylinder is dual circuit type of unknown bore and once again may not the original part - in fact, using the Minisport catalogue as a spotters guide, it looks like an '85-on one

When all is said and done, the front/rear brake balance seems about right so I will probably keep to the 19mm cylinders unless anyone comes up with any definitive info.

PJ

[Tim]

So, does ayone know:
a) were the roll pins in different places on different sized cylinders to ensure the correct size would be fitted.

Yes but offhand I can't tell you which one is which.

b) what size should I have on a 1981, 1275 Californian with 8.4" discs and standard twin piston iron calipers. Master cylinder is dual circuit type of unknown bore and once again may not the original part - in fact, using the Minisport catalogue as a spotters guide, it looks like an '85-on one

First off they are imperial, so 19mm is really 3/4", which were used on most of the drum braked Minis and Mokes. I changed to 5/8" (Cooper S) ones, on my car when I fitted Metro 4 pot disk brakes up front. However the late model Australian Mokes like yours were fitted with 11/16", I believe.

When all is said and done, the front/rear brake balance seems about right so I will probably keep to the 19mm cylinders unless anyone comes up with any definitive info.
PJ

This is the most important thing. I've found that when fitting disks the 3/4" rears lock up way too easily, however there are other factors such as the difference between master cylinders and proportioning valves, as I've only ever fitted disks to models earlier than yours. If you find that the backs lock up, just change them for smaller ones. The backs do very little in the way of braking anyway.

Tim

[PJ]

Thanks, Tim

It's a long time since I was grubbing around under Minis, but it's all begining to come back to me now. All the mini variants that I've had before had a pressure limiting valve on the rear face of the front crossmember of the rear subframe. (We sometimes modified this to make it adjustable and mounted it inside when putting the brakelines inside for off-road use). My Moke has a bigger-bodied device on the inside of the right-hand sidemember of the rear frame, with the lettering 'FRONT' cast into it with an arrow pointing (surprise) forward: This has prompted a hazy recollection from my days at Longbridge (1970s) of some export markets having an 'inertia valve' in the brakeline to cut the pressure under heavy braking. The Haynes manual has nothing about this and none of my parts catalogues make any reference to this sort of thing - do you know anything about it?

[Tim]

PJ, although I've never seen one (my Mokes have all been too old) the later cars did have an inertia valve. There was a recent thread on the Australian Moke forum about them.

http://moke.com.au/Forum/index.php?topic=3248.0

My parts book lists 13H7757 Brake Inertia valve, dual line brakes without limit valve, Moke 80-81

a quick bit of googling

[img:355:318]http://www.minimania.com/imagesbig/13h7757.jpg[/img]

Tim

[PJ]

Tim,

That's the thing! seems to work o.k but the standard front discs aren't that hot with the torque that 13" wheels put on them. I'll see what happens after I've upgraded the front, but for the time being I've gone for a pair of 11/16" cylinders and will keep the inertia valve as is. Back on the road tomorrow, I hope.