Need help with a brake caliper
 

Hello all, my 1991 740 is on need of another brake caliper for the rear passanger wheel. The bracket that the bolt goes through to thread into the wheel hub has broken somehow and have to replace it. I went to the autoparts store and they found two brake calipers for the car. One is a 40mm caliper and the other is a 38mm caliper. They said that I have to measure the inside (think they said inside) diameter of the piston to get the correct measurement, but I don't have the tools to get the measurement. THe price difference between the wo being almost $20.
What I also found is that the markings on it says something like "Ate" or "Air" for the company that made the part. Could that tell me the size? Any help is appreciated.

ATE *is* one of Volvo's brake manufacturers, but I don't know of any correlation between that and the size.

I would be very hesitant to use any brake calibers from a local autoparts store, who knows what chinese junk that might be.

VADIS (volvo's parts catalog) claims your rear brake calibers are marked 38 or 40.

> 3530757 marked 38
> 3530758 marked 38
> 3530759 marked 40 repl 1 pcs 9140392-3.
> 3530760 marked 40 repl 1 pcs 9140393-1.

(so the 914039x numbers are older PNs, replaced by the 35307xx numbers)

oddly, both versions use the same rotors, and the same pads, but it makes sense that the left and right sides would have to match.

if you have a reasonably accurate small metal ruler, you should be able to measure the diameter of the piston hole after removing the brake pads...

40mm is 1.575 inches, or 1-37/64ths inch
38mm is 1.50 inches.

Thanks, I'll take a look at the numbers and have a small ruler on hand.