Calipper rebuild advice needed....

[Zithlord]

I am in the process of rebuilding my 1971 911 S rear calipers. I have bought the Porsche rebuild kit, rubbers and retaining ring. I have decided not to split the calipers. The pistons had some discoloration from corrosion, but look perfect when polished (se pic) The outer barrel, outside the black rubber seal is a bit corroded. Can I use a 3M scotch guard pad to scrub away the corrosion and polish that area afterwards? The piston moves easily out and in, in the barrel.

Thanks
John

[Zithlord]

I have now polished of the corrosion in the outer part of the barrel, is this ok to use? The piston runs very easily in and out of the barrel.

The other is before pic of the caliper...


John

[davep]

That looks pretty good to me. The outer portion can get very crusty, and that is generally where it wants to bind. Keeping it from rusting again is the real trick. I use a Q-tip to clean out the O-ring channel. Flush with alcohol and blow it out with air until it is spotless. I always use assembly lube on the O-ring and on both the bore and piston when assembling. I don't like using brake fluid since it is hydroscopic, so I want to keep it away from the outer bore area.

[MrJTP2001]

You could use the scotch pads to clean the outside portion of the piston but it already looks cleaner than most I've seen. The only seal that needs to be clean and no scratches is the seal between the rubber o-ring inside the cylinder and the sides of the piston.

In you first batch of photos I was going to say you should clean up the outer edge of the cylinder but it seems you did that in the second set. That helps the dust cap keep the area as clean as possible. In the second set of photos you also seem to have done a good job on cleaning out the groove for the o-ring and eliminated the rust on the outside of the cylinder.

At this point all I'd do is flush everything good with alcohol, let it dry then lube it up with caliper piston/o-ring grease and put it all back together. Flush it so that you are confident there are no pieces of rust or any other debris in the cylinder or in the tubing between the cylinder, bleed valves and the supply openings.

Hopefully more people will come in and add more comments.

Also nice job on refinishing/painting the calipers.

[37yrold911]

use the magic brake caliper paste that Porsche dealers sell

I would never put engine assembly lube anywhere near the brake system -- if that was what was meant by assembly lube above...

[davep]

You are quite correct, I meant brake assembly lube. I got mine about 30 years ago from VW when it had part # B1 and was called 'Brake Cylinder Paste'. It came in a tube like toothpaste but is a blue gel. More than likely it is custom labeled Ate brand lube. Anything to do with brakes must be brake fluid compatible and rubber seal compatible. One only requires a small amount per caliper but alas my tube is almost gone, and VW has not carried the lube in 15 years. Eric Shea uses a different lube, so alternatives do exist.

[MrJTP2001]

Dave, you must have been posting your original response while I was writing mine. I couldn't think of the proper term for the grease so I called "caliper piston/o-ring grease"

And yes, I do have a blue tube of it downstairs and it appears to be made by ATE but the grease is yellow, not blue.

[davep]

Tony, is there a brand or part # on your tube? It may be useful to document the various brands of assembly lube so that the next person trying to find the appropriate lube stands a chance of locating some.

Just as there are special assembly lubes for engines and transmissions, each tailored to the specific use, there is the special brake component assembly lube as I mentioned in my previous post. In all cases the assembly lube must be compatible with both the fluids it will later encounter, the materials it is (or will be) in contact with, and the special requirements of it's application.

BTW, I started rebuilding brake calipers shortly after I got my first 914 back in 1975, and the 914 rear calipers are the trickiest calipers to learn on.

[MrJTP2001]

Dave, the tube has lots of numers on it and it is mostly in German. Its called Plastilube and its by ATE. Part number may be "Art-Nr. 03.9902-1001.2"

[davep]

Tony, be very careful because I don't think that is to be used in the fluid wetted parts.
03.9902-0501.2 Brake cylinder paste: For repair, assembly and sealing of hydraulic brake components
03.9902-1001.2 Plastilube: Prevents brake squealing and protects against corrosion
http://www.ate-info.de/wk1/appendix...._lng=en&c_id=6

It is the Brake cylinder paste that I use as assembly lube.