caliper rebuild ?

vwbill · Post by **vwbill** » Fri Oct 24, 2003 11:35 pm

Hey does anyone have any tricks to get the pistons out of the the calipers?
I got them to move in the caliper but wont pop out with air so far! I got one piston out. I should have just got rebuilds!! Do you have to split the caliper open and use a tool to pull it out or do I need to hook it up to the master cyl somehow? I thought you could pop them with air but I had it up there psi wise! 120ish! Do I need more psi or wd40,lol. Thx, Bill

raygreenwood · Post by **raygreenwood** » Fri Oct 24, 2003 11:46 pm

Put some penetrating oil aroundthe outside of the piston...push it in..blow it out...repeat. It will sooner or later come out. But...it sounds like an ugly rust ridge. Rust pits after fine honing are okay...as long as they do not overlap into the groove area. Ray

vwbill · Post by **vwbill** » Sat Oct 25, 2003 12:19 am

raygreenwood wrote:Put some penetrating oil aroundthe outside of the piston...push it in..blow it out...repeat. It will sooner or later come out. But...it sounds like an ugly rust ridge. Rust pits after fine honing are okay...as long as they do not overlap into the groove area. Ray

Been doin the wd flush and try to move the pistons. The one I got out has wear from the end about half inch. right above the set point of the piston.
I think I'm gonna just go for the rebuilds with the new pistons. How perfect do the pistons need to be, coating wise? You dont want to blow out a caliper! Thx Bill

raygreenwood · Post by **raygreenwood** » Sat Oct 25, 2003 8:03 am

Ok, what is keeping the piston in is the outer ridge of rust..right inside of where the dust seal snaps on. Its that 3/8"-1/2" band above the actual inner seal. Is that the area you are speaking of? It is actually of larger diameter compared to the rest of the cylinder...and does not contact the piston. Thats why it had room to collect water and rust. Thats no problem. Just clean it up. Hone these LIGHTLY with a 360 grit hone. Just enough to bring any rust peaks down. Finish them while sitting idly in front of the TV. In a circular motion...first with 600 grit...then with 1000 or higher wet/dry sandpaper...make these babies smooth. The pistons shoul only be cleaned with 600 or higher wet dry. If they have no major rust or pits...polish the pistonswith 1000 plus grit only.

Note: it is the pits in the piston...or a "pit line" that will disqualify the piston. Pits that are single....and half the width or less of the size of the sealing ring in the cylinder..will be fine. Its when they are wider than the sealing ring that they bypass fluid when the seal starts to harden with age.

If the cyliders are good...but the pistons are bad....save them. There are many many cars in the junkyard that use the same pistons...BMW's...volvo's...etc. Store them in transmisssion fluid, They will never rust. But..don't store any of the rubber parts in transmission fluid. Its worth it to measure the diameter of both the piston and a clean spot in th cylinder before you start honing. Take off no more than about .002". Preferably no more than .001" Ray