caliper rebuild help

[rjm428]

i pulled my calipers off my 77 s and broke open the back ones and got all the pistons out. then i read the pelican tech article on caliper rebuild that said not to break them open because it will be difficult to put them back together without leaks.
i tryed to remove the pistons on the front calipers without breaking them open and have one frozen piston. i used air pressue but no luck.

any ideas on leaks and frozen pistons??

[Vipergrün]

Can you get some heat on the piston? You'll be replacing the rubber seal anyway, so it wont matter if it gets thrashed.

[rjm428]

i might just have to do that but i don't want to damage the piston.

[rjm428]

any ideas on the rear calipers that i broke open??

[skinnerd]

I actually just finished redoing the brakes on my RS replica....S calipers in the front and the M's on the rear. Both of my rear caliper's had basically frozen pistons (or at least really, really stuck). Couldn't budge them with air. First I finished rebuilding the fronts (which were cake as I had used new SS pistons last time, so only needed new seals/dust covers), and remounted them along with the nifty gas slotted rotors and installed the new pads.

Next remounted the rears, and bled the entire system. Then removed the pads from one of rears, and proceeded to use the brake pedal to push the non cooperating pistons out, one caliper at a time. When I got them out it was obvious what the problem was. The piston bore outside of the seal and the piston had both rusted up a bit. I replaced the old piston with shiny, shiny new ones. I used my little dremel tool with some wire wheels, sanding discs and scuffing pads to clean the rust out of the outer piston bore. It was really shiny and smooth when I was done. The new pistons easily moved in the redone caliper bores.

It was easy but time consuming having to rebuilt one rear caliper and installing it, before again bleeding the system in order to blow the pistons out of the remaining rear caliper.
It does work though.
Your master cylinder can apply a lot of force.
Finally I cleaned up the old rear calipers and applied a little "faux" cad plating, so they looked a little better when I reinstalled them.
Before:

After:

New rear rotors as well, because the stuck rear pistons allowed the pads to drag wearing down to the metal to quickly and eating up (scoring horribly) my existing rotors.

I used the handy self bleeding system as offered by our host.
Worked like a charm....best money I ever spent.


Finally, I also installed a new set of AJ USA brake cooling ducts up front as my original Holbert racing fiberglass versions had bit the dust many track miles ago. These news ones are fab'ed in aluminum so should last for quite a while.


Redoing the brakes takes some effort and patience, but the end result is well worth it.
Can't imagine what the dealer would have charged for this?
And I likely did a better job to boot.

Now I can stop like I ought to....

[skinnerd]

I didn't split my rear calipers as I had heard that getting them to seal again could be problematic.
Luckily I didn't need to, as I use the car's hydraulic system to force the pistons out one caliper at a time.

[skinnerd]

Here is a good pic on how shiny and smooth I was able to get my rusted piston bores....

[Emission]

Originally posted by skinnerd
Here is a good pic on how shiny and smooth I was able to get my rusted piston bores....

Wow! Nice job!

[skinnerd]

Actually I might be in error with that last picture... at closer inspection that looks like the inside of the new piston. I think you can see the new dust boots in place too. And the angled step in the outer edge of the piston that gets oriented just right to reduce the pad squealing.

Maybe with these you can see the difference.
Previously the outer ~1/4" of the piston bore was quite rusty in this first pic. It appears very dark in color.

Where afterwards after the dremel had done it's thing, you can just see the outer portion of the piston bore in this pic I think. Much smoother and shiny.

[rjm428]

looks great!
where did you get the new pistons??

[skinnerd]

I got the rears at Stoddards....they were not too bad in cost either from what I remember. The old ones were just in bad of shape to reuse I decided. The fronts I had already changed out for stainless steel versions 10 years ago...they still looked perfect.

[safe]

Air sucks. Reconnect caliper (and bleed) and with a piece of wood between the pistons push the breaks. Make sure both pistons comes out.

[cmc140]

I also have a 77 and split all of my calipers, prior to reading anything about it on this site. I purchased new o-rings from the Porsche dealer and have had no issues with them leaking. I did torque the ever loving shizz out of them though. My fronts I actully cut two of the bolts off when splitting and wound up drilling the holes out to 3/8" and ordering ARP 12 point bolts because you can't buy any of the factory bolts. I saw someone on the board that had done it.

[rjm428]

thanks cmc 140

i'll call hendrick porsche and try to get those o rings.