A puddle under the left rear tire meant I'd be replacing the piston seals on my 79 stock brake system a little sooner than I had expected. When I removed the old seals, it appeared that the lower seal had the fold (or "v") pointing to the top (brake pad side) of the piston. When I tried to reinstall the pistons this way, the seal ripped. So, I tried reversing the seal and put the V part of the fold facing the bottom of the piston. Went in without ripping; however, they now leak when I get the air out of the system and pump the brakes hard. (1) which way does the fold of the piston seal point - to the pad side or the botoom? (2) if the fold points towards the pad side, how on earth do you get the piston back in the cylinder without ripping it? (3) If the fold points to the back side (allows easy installation of the piston), should I be looking at replacing the pistons themselves next or opt for an entire caliper assembly? Thanks.

 

fold should point toward the pad, that way when you get on the brakes hard the pressure pushes the seal into the bore helping it to seal better, otherwise the brake fluid will just push past the seal and leak. When I did my brakes I went to o-ring seals, but the seals in the control valve are pretty similar to what you're doing. With some patience you should be able to work the seal lip into the bore by going around it with a small screwdriver, or you'll need a thin sheet of stiff plastic or metal you can wrap around the seal to compress it while you slide it in. Patience is key, but luck never hurts either

 

Cmac72 - I know what you're going thru. Just rebuilt my calipers. The fold does indeed go towards the pad. It's a major pita to get the pistons into the bores. I ended up tearing the first set of seals. Went out and bought another set. Take my advice. Dip the seal in brake fluid and rub some on the bore (where you're putting the piston in). Then place the piston with the seal over the hole and apply a light bit of pressure. Use a very small flat screwdriver and gently push the seal in the bore. Push in about a centimeters worth of the seal. Then go to the opposite side and push in about a centimeter there. Then gently push in the remaining part of the seal. When you have the entire seal lip in, then push down on the piston to get it into the bore. Some have said they use a feeler guage instead of a screw driver which also works. I felt more comfortable with the screwdriver though. Just make sure you choose one that that is blunt on the end to lessen the chances of cutting the seal. The first one will be the toughest. You'll soon get the hang of it and be able to completely install one in 30 seconds or less. The key is to gently push the seal in at use just the right amoun of pressure when pushing down on the piston. I push just hard enough to get the lip to drop down when using the screw driver but not hard enough to get the piston ****-eyed going into the piston. Make sure you don't forget to put the springs in first. Nothings worse than spending 10 minutes on the first one just to discover that you forgot to put the spring in. You might get tiny cuts in the seal from pushing in with the screwdriver. I think this is okay. I haven't completed the job yet but I think it'll be fine. I think it's impossibe to get the seals in without putting tiny cuts in the lip of the seal. I think it should seal fine but time will tell. Good luck. It's a pita.

 

Thanks very much. That will be a big help when I try AGAIN tonight. I do know what you mean about forgetting the spring!

 

When I rebuilt mine, I took a piece of plastic tube and cut it in half length wise. I put the halves around the piston to compress the seal and pushed the piston into the bore, just like compressing the rings on an engine piston before inserting into the block. It still was a pain, but by the second or third piston, I got real good at it.

 

Another good idea to try. Glad I purchased that extra set of seals! Thanks.

 

Thanks for the advice - tried the feeler gague method and it almost seemed too easy. Did some bleeding but didn't get a chance to finish. Didn't see the rush of fluid I saw before, so (hopefully I won't jinx myself) maybe it will work. Will find out in a couple of days when I have time to complete the bleed and take it out - after the next four days of rain, that is. Thanks again.