S3 rear brake cylinders

S3 rear brake cylinders

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mentall

Original Poster:

453 posts

131 months

Tuesday 2nd December 2014
quotequote all
Here I am again after 18 months of lurking: thanks for the endless stream of useful and essential information.
One of the problems on the 'warning to prospective buyers' car was, of course, that the Saab servo was rotted out (no brakes, over-fuelling). I've now fitted a combination of Ka parts to get the 22.2mm cylinder / 8 inch servo required. I won't brag that it works until I can test it, which I can't because the rear wheel cylinders are rusted up.
Now here's the thing: the Lucas 64677523 / Delphi LW37523 reference that you kindly give shows a cylinder with a bore of 20.6mm and pistons with domed shiny ends, and I've seen the thing at my local factors. But my car has 19mm pistons that are slotted to receive the shoes.

What's going on?
And I promise not to lurk any more!

mentall

Original Poster:

453 posts

131 months

Wednesday 3rd December 2014
quotequote all
Thanks, guys. Here's my shoe and piston:



The piston doesn't look like yours, or the one in my Haynes Sierra V6 book. However, the shoe does look the same, so I'll buy the LW37523 cylinders, fit them, and see what happens.

Stewart, I think you may be right. Or maybe it's the old 'TVR threw on anything they could find' syndrome.
And last year GadgeS3C said he thought the pistons should be 19mm diameter. His car's a 1991 (mine's 1990)

Still a little concerned about the bore size, though: 19 to 20.6 bore is an 8.4% increase in diameter, 17.5% increase in area: a big change in rear:front braking effort.