Rear brake caliper piston size

[Casheye]

Hey Peeps,

I know that the 940 Estates came with a 40mm piston on the rear Ate brakes but would I notice any difference by using 38mm piston calipers?

The car itself is just a grocery getter and I'd rather not pay tripple the price for the 40mm over the 38s

Thanks in advance.

[J liddy]

Yes rear calipers are different sizes from what I'm told if piston is a couple of millimetres smaller it doesn't mater I may be wrong I have a new pair which are smaller but was told are fine to fit

[classicswede]

The important thing is to have a pairthe same size

[jpliddy]

thanks for the info Dia THAT DOES MAKE SENSE , think the pair you sold me are 36 mm so just a little bit smaller than my original callipers

[Forrest]

There is information in the FAQ about identifying brake components including how to decipher the code on the VIN plate which says which brand were originally fitted front and rear.

By this stage in their life-cycle previous owners or mechanics could have swapped almost anything in by now.

I think 40mm rears were most common on the late model estates. If replacing both at the same time that is what I would probably try to go for. If only replacing one then it is more import to match the opposite side to avoid introducing an imbalance. 40mm piston will give about 10% more stopping power than 38mm for the same hydraulic pressure as the force relates to the surface area of the piston.