What kind of rear brake cylinder do I have?

[apblake]

I want to rebuild the rear brake cylinders on my Cooper S. The question I have is: does anyone recognize what type of brake cylinder I have? It has a 29 on it. Would it be original to the car or is it a replacement? Is it worth reconditioning, or should I just buy new cylinders? Any problems with modern rebuild parts for the cylinders from minispares?

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[minibitz]

The stamped number will be a manufactures casting number, so no clues there.

Take a cylinder off, pop out a piston and measure the bore to be sure of which size fitted.

Cylinder can be rebuilt but why bother when replacements are so cheap? I've used genuine and Minispares cylinders. They all seem to last equally well.

[AndyPen]

I'd say just go for original spec (size) replacements. Last year I helped on a car that had been having a few issues for years. It had different bore cylinders on each side - ha ha.

[Exminiman]

I'd say just go for original spec (size) replacements. Last year I helped on a car that had been having a few issues for years. It had different bore cylinders on each side - ha ha.

Really good point this - replace cylinders, springs, shoes on both sides together (and maybe have drums skimmed)

[CooperTune]

To large a dia. rear wheel cyl. will cause the rears to lock up early. I use 1/2 inch rears with an adjustable bias valve. 5/8 inch with std bias valve and std Cooper S 7.5 disc and calipers. I have found the Mintex shoes are clearly better quality and as cheap as drums are skimming would be a waste of time. Steve (CTR)

[apblake]

Ok if I look in parts manual AKD 3509 it appears that the correct cylinder for a hydro car is 17H8773. If I look up that part number nobody seems to carry it, but it appears to be a 5/8” bore. Strangely, unless I’m just not seeing it, minispares doesn’t seem to have a 5/8” bore (but Somerford does). Can someone confirm that 5/8” is the right size for a 66 built Cooper S?

[GraemeC]

Minispares:
http://www.minispares.com/product/Class ... 0to%20shop

[woodypup59]

To make sure the different sized cylindrs couldn't be mixed up, there is a roll pin in the mounting face which fits in the backplate.

The position of this pin, and the hole in the backplate differed according to the application, but this feature has become blurred over the years.

So you may have to re-drill the backplate when you get your new cylinders.

[minibitz]

Ok if I look in parts manual AKD 3509 it appears that the correct cylinder for a hydro car is 17H8773. If I look up that part number nobody seems to carry it, but it appears to be a 5/8” bore. Strangely, unless I’m just not seeing it, minispares doesn’t seem to have a 5/8” bore (but Somerford does). Can someone confirm that 5/8” is the right size for a 66 built Cooper S?

Yes, Mini Spares do have 5/8" - GWC1101 or GWC1101MS

[apblake]

Thank you gentlemen - makes much more sense that they should have it. For me it doesn’t show up in the rear brake section - only if I search for it.

[iain1967s]

There was a problem at one point with the circlips used to retain the cylinder to the backplate.

They were made from non-sprung metal, and so would deform or break during fitting.

You should be able to reuse the old circlips if you pry them off gently…

[apblake]

Ok thanks Iain - I’ll keep this in mind