H1 Hummer Rear Caliper Rebuild

[drdonpalmer]

Hey all,
Got a leaky rear caliper and its leaking past the piston thru the dust boot. I've rebuilt calipers before and its a piece of cake, but I knew this was going to be a bit tougher. Bought a kit from the hummer dealer that contains two pair of piston dust boots and piston seals (enough to do both rear calipers) for about $17. BTW a remanufactured caliper is about $180 and a new is upwards of $580. $17 for two calipers sound really nice. Once the caliper was removed from the vehicle and with the 2000 Hummer service manual in hand, I proceeded to disassemble the caliper.
Now I had already started the disassembly prior to consulting the manual...I'm a typical guy...so I had the bleeder screw out, the input fitting out, and added some compressed air to push the piston out, when I noticed I couldn't get the piston free. It didn't work like other calipers. Then again, this piston is on a thrust screw so its going to be different. So I consulted the manual finally and noticed I was suppost to remove the parking brake spring and retainer, then remove the PISTON RETAINING SCREW! There it is, makes sense. I didn't bother with the parking brake, I went for the retaining screw which on the manual diagram shows it clearly in the face of the piston which contacts the brake pads...a big flat allen bolt basically. Only one problem...mine didn't have that, at least not visible. It is covered by a metal cover which looks pressed into the piston and apparently covers the piston retaining screw.
So here is my queston finally: Has anyone got any bloomin idea on how to remove the cover? Its not on the manual diagram. A saginaw pump has one of these and you remove a big metal snap ring and then spin the piston into it which presses it out from within, but I couldn't figure out how to do that with the caliper piston. UNLESS, by removing the parking brake spring and retainer, that is how it is done, but I didn't perform that step...at the time it didn't seem to me to be the answer. Has anyone done this rebuild?
Bottom line, I had to get the rig together again, so I removed the old dust boot, replace it with the new, hoping it would fix the leak only to drive it again for an hour and find it leaking again. Leak is definitely due to the piston seal.
Thanks in advance,
Dr. Don Palmer

[drdonpalmer]

Ok, I found the following site with diagram and unlike my manual it does show the "piston cap" in which I was referring. The problem however, is that it simply states "remove the piston cap", HOW? is the question.
http://www.hummerknowledgebase.com/brakes/rco.html
Thanks,
Dr. Don Palmer

[ssgharkness020147]

http://flashoffroad.com/Maintenance/Brakes/Brakes2.html

[drdonpalmer]

Thanks for your reply. However, the rebuild of the caliper and the removal of the piston cap in particular is not explained in the article. It is a great article for doing your brakes however and I did reference it when I completely replaced my rotors and pads.
Well, looks like I either destroy the cap to remove it or I get a replacement at the dealer....unless some of you respond in time.
Thanks,
Dr. Don Palmer

[ssgharkness020147]

You have a PM Doc.

[drdonpalmer]

Ok, First I want to say thanks to Harkness for all your help. I appreciate it.
I read through everything I could get my hands on and how to take the piston cap off still was not explained so I just decided I was going to destroy it so I could get the caliper built.
Now in-case your reading this at a how-to and I just lost you, keep reading because it has a happy ending.
I put the caliper in a vise and started laying into the edge of the piston cap with a small screw driver and a hammer until it peeled back enough to get a pair of needle nose vice grips on it, but that didn't work. Until I got two areas on the cap peeled back and with the vice grips attached I struck the vice grips with a hammer and the cap came right off. The cap is very maliable and I was able to easily correct the damage I cause to it and when I pressed it back into position after the rebuild, it looked as good as new...well, very close.
See Pics...well, I have pictures, but can't install them. I'll email the pictures to someone on here if they will post them.
Now as for the rebuild...I ran into some more snags. One is that the kit includes a dust boot and a piston seal, but DID NOT contain an o-ring for the piston retaining screw. Since it looks like that was part of the cause of my leak in addition to the piston seal, my caliper is still leaky, although a lot less, after the rebuild. I will be obtaining a new o-ring to correct the problem.
Another problem was getting the piston back onto the thrust screw and back into its bore. You have to follow the instructions and engage the parking brake lever because it puts pressure on the cone clutch on the back of the piston so that when you turn the piston it will actually thread on. Without that pressure, you will turn the piston, but the cone clutch will just stay stationary and your piston assembly will not advance into the bore. Now that's how its suppost to work, but I couldn't get mine in even with the above procedure. I'm sure I'd STILL be trying to get it into the bore if it weren't for the fact I had the piston compressor for the FRONT calipers. I have BOTH piston compressors, but the rear one won't work unless the piston is in about a quarter of the way and despite a very large C-clamp, it wasn't big enough for the very large rear caliper the H1 uses. So with the front compressor and a large washer, I was able to use the parking brake lever in combination with the piston compressor, while turning the piston with some very large channel locks, to get enough pressure to get the piston installed.
As with anything, now that I've done it, it is really a cinch.
I hope this helps someone in the future, because I could have used this thread.
Thanks again Harkness,
Dr. Palmer

[Ground hawg]

Thanks for the Info, I replaced my drivers side rear list month with a rebuilt from Bluehummer. I spoke to Dave before I purchased from him. the rebuild Kit is quite easy but it takes about 4hrs from start to finnish acording to Dave. and there's always the possabilaty that it still aint going to work right. I opted for the $185 for the rebuilt unit which was at my door the following morning. then went to work and did some O/T to pay for it.