EmboRotary

Hi all,

I recently rebuilt the rear caliper on my S3 as it had seized. When I removed the piston, I found that the rust and pitting had damaged it down to about 7mm from the top. In order to get the car driving again, I rebuilt the caliper with the damaged piston and so far it has been fine. Now I need to replace the rear pads and I'm certain that once I push the piston back, the seal will go over the pitting and leak.

So my question is, does anyone know any part numbers for rear brake pistons? I've found one on eBay that looks the same, but it doesn't have the internal mechanism for the handbrake included. Is this easy to fit, or should I find one with the mechanism included?

Also, I've looked around, and the dimensions for the FD's rear pistons are exactly the same, and from memory, the handbrake mechanism looks similar, are these interchangeable?

Many thanks

LongDuck

To my knowledge, the S3 rear calipers are identical for 2nd and 3rd Gen US spec cars, but you'd need to have them side by side to compare. The parking brake mechanism is built into the piston cup, so an eBay replacement without that design obviously won't work. Have you considered honing the bore of the caliper to clear out the rust and corrosion?

Changing brake fluid is often overlooked maintenance and leads to these types of problems as brake fluid is hygroscopic and absorbs moisture from the air in the reservoir.

EmboRotary

It's not the bore of the caliper that is the problem. The top seal of the caliper was broken and allowed rust to form on the piston, and now that the piston is pitted, it will leak once I put it back in.

KansasCityREPU

iTrader: (9)

I don't think it will mater. As long as the seal fits, the only part that maters is the otter portion of the seal and the piston bore.

yeti

iTrader: (1)

I recently went through this exact same experience. I ended up finding and buying used rear brakes for an arm and a leg.

Here was my process. I learned that all rx-7s use the same bore. I bought FD rear pistons (what I found on ebay available new for UK) however, the pistons I bought didn't have the guts on the inside and even if they did FB pistons are female and FD are female. Can't find a photo example of the different styles quickly at the moment. Some pistons have a "nut" inside and others have a screw so that you can rotate them to retract. While others nothing and you push these back to retract them. There may be other designs. Anyway, after sending the FD pistons back and losing time and money, I did more research and started look at what other vehicles used the same caliper rebuild kit and compared with what was available to look at in my local junk yard. My local junk yard doesn't have many antique cars as that's what the rebuilt seal kit referenced so comparisons were few. I did manage to pull one apart in the yard and it was also the "male" style piston. I was running short on patience and time and decided to buy a pair of FB calipers hoping they would be in serviceable condition. There was still a small pit on the $300 pistons I bought. But the other piston was in great shape.

You could (if the pitting is minor try jb welding the pit? May still leak though. There is also pink piston grease (that I didn't use at the time) but that might help with the issue? Here is the grease: https://autoparts.toyota.com/product...00g-0888701206

Good luck and if you figure out a solution please let me know. I'd like to have a backup on the shelf.

EmboRotary

I managed to find an FB rear piston on eBay, but it doesn't have the handbrake mechanism. I've ordered it and will update you on how swapping the mechanism goes. The FD looks very simple to swap, just one circlip holding the guts in. However, from memory, the internals of the FB looked a bit more complicated. Seemed as is there was a bent rectangular piece of metal holding everything in.

But anyway, going to give it a good old college try when the piston arrives, hopefully tomorrow. Then I can stop this horrific brake squeak!

KansasCityREPU

iTrader: (9)

Seems like it might be easier to make a caliper bracket to hold another makes caliper. Maybe something from a Mustang. I don't have a Mustang caliper but I am willing to donate my time and CNC plasma table to anyone that comes up with a bracket design willing to share with everyone and not make a profit.

j9fd3s

iTrader: (3)

i believe that the Mazda part number is FA18-26-660A, https://www.amayama.com/en/part/mazda/fa1826660a