I am in the process of going to a front disc setup on my 68 malibu. I am also rebuilding the rears with either rebuilding existing or getting new rear wheel cylinders. Question is this: Local parts store asked if I had disc or drum up front because the rears (cylinders)are different sizes. The setup is from a 72 monte (complete w/prop valve, lines mc/booster, calipers/rotors, everything) I guess the inside diameter of the cylinders is different. Which do I get, the bigger rears or the smaller? Thanks.....

Their should be only 1 size for the rear slave cylinders...it should be 15/16" bore. The front slaves on a 4-wheel drum are bigger than the rears (1-1/8" bore fronts). Someone else chime in if I am wrong, but I am pretty sure this is correct.

I replaced mine one wheel at a time. First time I went to the parts store and they just handed me a cylinder. Second time, they asked what size. I didn't know and took the one that looked like what they gave me last time. Got it back to the car and the one one the car was the other size. However, my car was 4 wheel drums and I converted to disc. Never heard of their being different rear cylinders for disc or drum.

I'm gonna guess I have the wrong ones because these have the rubber boots wrap around the ends of the cylinder and it rubs on things in the brakes. You want the ones that are metal on the edges. If you see them both together, you'll know what I mean. Not sure which is what size, though.

Tim.

I replaced the rear wheel cylinders on my 67 chevelle. I believe there is only one size from 1964 to 1969, 15/16". That's what I used, it worked fine & that's also what my books show.

I just replaced both front and rear cylinders on my 69 cutlass drum brake system all around. It is the same as chevelle. It had bigger cylinders on front than rear, the sizes as described by ehjorten.

I have never heard of the rear cylinders being different dimensions, and if they were, they would most likely be included in aftermarket disc brake kits (or at least recommended).

I think the guy in the store got the front and rear cylinders confused. Remember that they will ask you about drum/disc brakes every time, even if you're just looking for a radiator cap ;)