Turbo caliper "scraper ring" replacement guidelines

[sandiego]

My 1986 turbo 911 caliper has the normal Sealing Ring but also a "Scraper Ring" (930.351.547.00). Are these routinely replaced during a rebuild or "as required". If the latter, what are the guidelines for determining if replacement is necessary? FYI: each caliper requires 4 Scraper Rings @ $25 each.

[T77911S]

what I would look at is how easy does each piston go out and go back in.
I may be wrong but if you have some pistons that move more freely than others then that could cause one side to brake more than the other resulting in one side locking up before the other.

I did this about a yr ago. do a search, I think you can get them a little cheaper.

to get the pistons out a 2x4 fits inside the caliper. use comp air to pop them out.
I think the groove that the scrapers sit in is beveled so that the top edge of the scraper sticks out.

when I put the new scrapers in I literally could not get them in. the one I managed to get it and almost could not get it out even with coating the scrapers and pistons with brake fluid.
I ended up putting a little grease on the scrapers so the pistons would slide in and out.
with this I was able to get all 4 pistons to pop out at the same time.
I don't know if this was the right thing to do but a situation came up and I had to get the car back on the road.
as long as you don't have fluid leaking past the pistons and if your are not popping out together, you may try a little grease to getting them moving more freely.

hindsight that is what I would have done. I wanted all the pistons to pop out the same and I thought new scrapers would do it.

oh, don't mess with that outer seal unless it is bad. that one is really expensive.

I also flushed all the brake lines and MC and put new fluid in.

[reachme]

most of these cars are not getting a lot of use, the brake dust can get hardened on to the extended piston. If that happens and you jam them back with a C Clamp then you create a leak. That was me. I learned to clean them off with brake fluid and light coating with brake assembly lube to before pushing them back.
Also use a old pad to push them back in at the correct angle. Wrong angle and you will be opening up a leak.
When it comes to popping out the old pistons for a rebuild its best to prevent them coming out all the way. If you do then that is the only one that will come out and all air will flow out that hole. Keep pressure on and let them move slowly. The other problem with popping out is you create a cloud of atomized brake fluid that immediately floats toward fresh paint.

I was worried that brake effectiveness fades and it's hard to tell when they are somewhat degraded both in operation and in retracting pad from rotor properly. Rebuilding is the best way to know the brakes are as they should be and that is why I rebuilt the turbo front brakes. Also one of the pistons was not retracting smoothly on a pad change.

I did replace the scraper rings when I did it (while I'm in there). Not that hard to get in, I use the brake assembly paste which is basically clear grease that does not degrade the rubber and as you circle your finger around they pop into place.
also those scraper rings have a certain direction they need to be installed in. Look at the colors on the outside of the band and you will see. pic below.
Hope that helps

[T77911S]

the pistons are not like normal pistons, there is a coating on them that can be damaged very easily. the 2x4 stuck in there keeps them from popping out all the way plus it gives them something to hit that wont damage the pistons.

never heard about orientation of the rings.
I did take note of the colors and could not figure out a pattern when I removed the old ones.

use the grease