Stan944

I bough a rebuilt brake caliper, and they painted it all, including the tapped holes for the brake line and the brake bleeder screw. It probably was powder coated; I don't know how to tell.
The question is whether I'll get a good seal at the brake line and the bleeder?

AznDrgn

It'll be fine, the threads don't make the seal on brakes it's the flared ends that seal up and a little paint or powerder coating on they shouldn't hurt. If you are truely concerned hook it all up and in a week back it off a little and then reseat it again. A week should be enough time for the brake fluid to eat up anything that might be in it's way and when you reseat it it'll be metal on metal.

Scott at Team Harco

Yep - good point. The sealing surfaces are in the ports. Hopefully, there is not paint on those surfaces.

I don't understand why they wouldn't have plugged them before painting. Hopefully, they didn't take other short cuts in the rebuild.

Stan944

Thanks, I know that the seal is not through the thread, but the flared end. It IS painted.
I could keep it in a brake fluid for a while ( a week seems long...)

Well, another short cut: the pistons are not properly oriented. I don't have a proper tool to rotate it; am thinking about using a pipe expander and a ratchet.

Another question: from previous experience I could push in/out the pistons with my hands only; barely, but could. I can't do it with this caliper. is it normal?

But it was cheap (CAD$84.00), so I'm willing to spend a little time to make it work.

Scott at Team Harco

You may want to disassemble the caliper to make sure it was rebuilt properly. This will allow you to orient the piston as you choose and also verify piston movement. It will also allow you to see if the seal was lubricated and the condition of the external surface of the piston as well as the condition of the bore. You will also have the satisfaction of knowing everything was put back together properly.

Stan944

yeah, that's what I probably should do. Any recommendations on how to remove the piston? I heard about using compressed air, but that would mean a shopping trip to get some adapters between my tire compressor and the caliper...
I just made a call to a local store which has some tools to loan, and sounds like they might have the pliers to rotate the pistons. Do you think these pliers would have enough grip to allow me pulling the piston out?

Dave in Chicago

Just went through rebuilding my M030 front calipers.

Yes, you have to use compressed air to get the pistons out. Don't try to pry them out, just won't work and you'll damage a piston or bore. I took my little Sears tire inflater pump, cut the hose, and squeazed it onto the bleed screw. I capped the port where the brake line comes in, openned the bleed screw just a bit, and presto - compressed air power galor.

All I had to do was find a small enough aviation clamp to put the valve back onto the compresser hose after I was done. The hose was a pretty good fit for the bleed screw (lucky). I did not need more than about 40 psi to get them all to pop out.

I also used this same set-up to "pressure test" the calipers after I had rebuilt them and before mounting them into the car. Ran up to around 100 psi with pistons shimmed to keep them from coming out to far... No leaks, so I assumed good seals and all. I've been driving it and will wring it out at the track tomorrow (yippee!).

Be VERY careful. The pistons like to move slowly and then pop out like bloody rockets. Keep fingers out of the way, wear eye protection, etc.

If it's the single piston caliper, then it's a bit easier as you will not have to shim the space between opposing sets of calipers to get them all out just far enough to remove by hand.

On my calipers, I could NOT press the pistons back in by hand. I had to use an old brake pad and a C-clamp to slowly and evenly press them back into the bores. I lubricated the seal rings with clean brake fluid before install, same for the pistons. It's a tight fit, especially with new seals.

They must go in dead straight or you will scratch the piston/bore surfaces.

Stan944

Thanks for the tips.
I like the idea of testing for leaks with compressed air, makes me wonder what are the maximum brake fluid pressures upon very hard braking?
I test the calipers when connected to the system, by disconnecting all brake lines (except for the one I'm testing) at the master cylinder and replacing them with a short brake line ended with a bleeding valve. After bleeding I push on the brake pedal as hard as I can. If the pedal is firm and doesn't sink (not even slowly), this caliper is OK. Obviously one isn't.

Stan944

Update:
Compressed air worked very well, and I'm glad I listened to your advice about opening things up. There is no way I'm going to install this caliper. The piston looks horrible, with deep scratches all over. Also the cavity for the piston was painted, including under the seal! To me it's a mistake, as the paint surface is not regular, and it would gradually flake off in contact with brake fluid. Although I haven't confirmed yet if brake fluid dissolves this paint. I'll make a new thread asking for reliable sources to proceed.

Mighty Shilling

rebuilding calipers is pretty easy, if you still have your old ones, you can pick up a rebuild kit from Paragon for $15.00 US. per caliper, and it will take 5 minutes to do.

Stan944

Thanks for the reply, but neither my existing nor the rebuilt one that I just bought are rebuildable, i.e. pistons have deep scratches. I don't think the kit for $15 from Paragon contains pistons, does it?

tifosiman

Correct.

5 minutes to rebuild a caliper properly? Someone needs to stop smoking the wacky tabacky.

Mighty Shilling

Hey! thanks Tifo! I was more meaning the context from starting with the caliper on the table and the air compressor turned on... to pop out the piston, make sure everything is clean, pull out the seal, put the new one on, grease everything, put the piston back in, and the new dust cap in place...

Stan, no pistons in the kit.

Dave in Chicago

Porsche's kit typically includes piston, seal ring, and dust boot. These are expen$ive!

Who would paint the bloody bore in a caliper? What's up with that?

Scratches in the bore or on the piston are problematic when they are below (inside) the seal ring space. You'll not get the required hydraulic seal to operate the piston properly. Scratches above this line are more "at your own risk". For your piece of mind, you want clean bores and pistons.

It is true, rebuilding the caliper from the "on the bench, all parts on hand stage" is pretty quick if it's just seals and boots. Cleaning, a light sanding of the bore/piston with 1500-grit sand paper can add a bit of time to it.

Also, it took me a fair amount of time to slowly press the pistons back in. Careful, careful, careful there.

500

Hey Dave,

Those are some excellent points. I've recently purchased a set of 951 calipers for my project and plan on re-sealing them as a precaution. Thanks to your posts, I will be very careful about pushing the pistons in slowly and carefully to prevent gouging the cylinders/pistons.

Thanks!