Sean F

Do it yourself. I did it once this season and I'm about to do it again this winter. It really isn't hard. I've read of some people having trouble with rebuilt calipers though. One watch out is making sure you have the pistons correctly aligned at twenty degrees like in the Bentley manual diagram. They'll be noisy and might wear funny if you don't. If you see pitting on the bore or the wall of the piston, throw it away.

RedlineMan

Have you ever them apart? I'm not aware that alignment is critical. The passages are large enough that some missalignment does not seem to be a problem.

OE o-rings from Porsche. You could probably use any generic ring of proper size, I'd imagine, as long as it was fluid compatible.

I reused the orignals. For a track car I would have replaced them.

Honing!

RedlineMan

Are they leaking? Not needed otherwise. If you know they were done, and they are not leaking, they are fine. Don't fix it if it aint broke, eh?

Yes, I've seen problems with them when pro rebuilders work too quickly and make mistakes (common), or DIY'ers don't know what they are doing. As long as you do not nick the seal, soak everything in fluid first, and get the piston in straight and square so as not to tear the seal, you'll do fine. I press them in by hand, by the way, so I can feel if they are going in straight.

Actually, the piston is the only critical surface. Nothing ever touches the bore. The piston floats in pressurized fluid, and the seal is the only thing that contacts it. The only surfaces that really count are the outside of the piston, the seal groove, and the mating surfaces of the halves/spacers.

If the piston is pitted, it can scar the seal. Obviously then you need a new piston!

Sean F

Good point about the bore, just be sure that the groove inside the bore is okay when you replace the inner seal.

When I say rebuilding, I'm talking about replacing the dust seals and rings and inspecting the pistons. I replaced the pads at the end of the season and noticed that the dust seals were toast.

kurt M

Why power hone the bore? Honing is for bores that have seals that move in the bore such as a MC or old school drum brake slave. 99% of the pitting or rust in the bore is in the area outside of the seal. This rust can be removed with a scrubber pad or fine sandpaper oiled up with brake fliuid and the pits do not matter unless they are 100% across the area and real bad. If it is real bad use it as a core for a rebuilt that is likely just as bad inside because someone else did the same.

The piston often makes contact with the bore BTW. The harder you push on the brakes the more contact is made.

A little trick to do after rebuilding and installing new seals. If you just install the pads flush/blead and drive you will likely find that the car feel like there is air in the system and you have a soft pedal. The brakes work but the pedal throw is longer. Before you kill yourself flushing the system with a gallon of fluid looking for a hard pedal you should pre load the pistons. Do this after you do a full flush/bleed and do one caliper at a time.

Remove one pad, pump the brake pedal until the piston moves in some and the space is too small for the pad to be put back in. Push the piston back just enough for you to wiggle the pad in. There should be some friction from the piston draging on the back of the pad as you put it back in. Do this to all piston/pads that were worked on. Reason. New seals are too "grippy" and will often have too much pull back of the pistons. This will make for a soft pedal and the MC has to back fill more fluid than normal. By pushing back on the piston to make just enough room for the pad to be wiggled in rather than pushing the piston foward to the pad after rebuilding you are taking out the seal pull back.

Rebuild or purchase rebuilt, reinstall, pump up the system, flush/bleed, preload.

RedlineMan

The small area of bore surface OUTSIDE the seal was rusted, and this jammed the piston in the bore! I had to grab the piston with large vise grips and turn it by banging the pliers with a hammer while using compressed air to blow it out!! A scuff pad aint gonna touch that kind of rust, Brudda.

kurt M

True! Thats what the fine sandpaper wetted with brake fluid is for.

RedlineMan

Pfff...

You've got too much time to kill... apparently. No Carpel Tunnel either, I guess.

Alan Herod

John -- I see it differently -- you have to much time to kill. At the track it is far easier (and quicker) to rebuild with the seal, scotch brite, and fine sandpaper (if required); then to split the halfs and hone. Those are part of the emergency repair stuff that goes. I suppose one could carry spare front calipers -- but then you would need two and if you wanted to be really safe you would have to carry all four.

kurt M

i don't think I have ever spent more than 20 min popping a set of pistons and cleaning up the bores on a 2 piston cast iron caliper and that includes the blobs of rust that came on my 69. More than one set has been field stripped and rebuilt at the track when a members set crapped out or did not pass Tech. No, I do not have carpel tunnel nor a carpeted tunnel but I have been known to mutter, cuss and fart unabashedly while making stuff in the shop if that is any help.

RedlineMan

Hah....

It took me more than 20 minutes just to get the piston out. But you win. Next time I get one this rusty, I'll save myself the trouble and just mail it to you. You'll have it sanded smooth in no time, so I gather.

Alan Herod

Kurt's expertise has saved many DE participants lots of track time, usually at his expense, and not just fixing brakes either. His workmanship is amazing as well.

I can't come anywhere near the 20 minute at the track rebuild time, but I keep the rebuild tools together, includes small block of wood the size of brake pad and c-clamp to hold one piston in while popping the opposite one.

kurt M

I did not know we were in a contest. I thought we were helping a novice mechanic with limited tools fix his brakes. Hell, I should have uploaded some cool pix and some links to shiny billet cut tools! That gives us car nuts chubbys. (Homer voice) Mmmm.. an-o-dized!
Whatever comes from the hands on your arms and works is fine. Some folks like to follow the KISS rules some like to make a production. In the end we are, for the most part, all looking to get it done right save a $ and or have fun with a hobby. Sometimes fun is being done sometimes fun is the action itself.

I like this one and view tasks in this light. "A complex system that works invariably evolved from a simple system that worked". 1/2 or 32/64?

Shoot me an old M binder. Done plenty of them pro bono and many under field speed strip conditions.

(Edit. Alan, All simple tricks from a simple mind. The check is in the mail anyway. Off season is getting boring already. )

Alan Herod

Not really a contest; but, his post was under performance section and goal is maximizing track time for everyone. Most should learn some of these techniques at home under no/low stress conditions rather then loosing track time or taking track time from others. Some folk's mechanical skills are better spent on more complex tasks like rebuilding spewing weber carbs with parts found on the ground in the paddock. Helping the newbie not loose track time.