sticking rear brake piston

[nightpilot]

been reconditioning my xj and when i got it the real caliper was stuck. took all calipers apart and cleaned. front seem fine. rear look best of all and rubber ring looked like new. piston is loose in caliper without rubber seal. with rubber seal went in real hard. had cleaned behind seal real well.

when driving regularly seemed fine but when sat for about a month the back brake was dragging and finally got stuck.

piston looks like new and oring seal looks perfect.

took off master cylinder and no spooge obstruction.

inside dust boot on caliper it looked a little like some corrosion or something. is there an anticorosive coating I can put in there. wonder if this is what got it stuck.

any ideas on this sticky matter.??

[Montreux_Blue]

Did you use a scrapper when you cleaned the groove where the rubber seal goes?

[bikerphil]

If anything other than brake fluid was used to clean off the rubber seal, it's possible it has swelled up. Chemicals will do that. JAT

[Montreux_Blue]

The reason I asked about the scrapper is because a lot of the junk that was in mine was stubborn and it was the only way to get it out. Also did you lube the piston with some brake fluid before forcing it back in?

[nightpilot]

yes, I cleaned out behind the rubber seal very well, it looked almost perfect before I even started to clean it. The PO, said he put pads on brakes and he might have put something else on seal but I did not.

I used lots of brake fluid to put piston in but it still went in hard. I wonder if the seal has become hard. Also the crud around the dust boot looked like possible corrosion stuff you see on aluminum and wonder if it could have contributed to sticking. I have not cleaned piston off again and I can see a line where it seemes to have stuck and it might be near edge of caliper meaning possible the crud may have contributed.

Is it possible to get just the rubber rings from anyone? If so I might put new ones in front too.

Is there any type of lube that would help things here or an anti corrosive i can put in boot such as wd40 or something. ?

[DGXSER]

You can get rebuild kits for the calipers (contains the o-ring seal and the rubber dust shield) for Specials and standards on Parts-n-more or from Georgefix on ebay.

as to the corrosion, you need to (if you did not) get all of it cleaned up before you put it back together. you can even take light sand paper like 220 grit or above to those areas. I would not use anything rougher than 600 grit on the piston or inner bore of the caliper, and I use WD40 with the 600 grit paper to get a very smooth finish.

[Rasputin]

I would go with a caliper rebuild kit. I get mine from georgefix on ebay. Good prices and fast service. Who knows what the caliper may have been cleaned with before you opened it up. Use only Brake fluid to lubricate the seal. Use of stuff like WD-40 will cause the rubber ring to swell and cause it to stick again. When you have it apart you can sand any crap off with a fine grit sandpaper. Careful to not sand too much.
Damn yer fast DGXSER

[tarzan]

When scraping the inside of the groove out,it is hard to get in there.I use a 90 degree dental pick.That way I can get the side wall of the groove that you can't see.Then I use a little piece of scotchbrite pad with brake cleaner on it to scrubit and the rest of the caliper with.
Also,if the o-ring is good,you could probably clean it real well with brake cleaner
and let it sit out in the air for a day or so.I read somewhere that will let the 0-ring come back to size.I haven't had that problem myself,so I can't verify it.

[DGXSER]

Well....sometimes I am...

As follow up to my note about WD40....you do want to wipe the bore out with brake cleaner and then brake fluid before you reassemble after sanding.

[nightpilot]

thanks guys, does anyone know if the internal components of the XJ brakes are the same as any of the XS models? The rear went together with much more difficulty than either front one, but the oring looked perfect - brand new as far as I could tell. the front brakes have an extra dust o ring that my mechanic said take out as it sticks, but the rear has none other than the boot. thanks guys

[DGXSER]

Never owned an XJ, not sure how similar or different they are. I do know that in stock formation the fronts are split. One works off the front master cylinder and one works from the rear master cylinder.