Front caliper rebuild

Hello all... I'm in the process of rebuilding my brake caliper. Didnt take long to run into a little problem. A frozen piston. The manual says under the caliper rebuild section to replace the entire unit and or take it to the shop. Don't no about that. My rebuild kit is on the way. Can I spray a penetrating oil to try and free it up. Does anyone have any tips or tricks to free the piston would be great.

Thanks a lot

 

You can either reconnect/bleed the caliper & pump it out with brake fluid (not ideal, mind eyes & paint etc!)

or use compressed air to blow it out (protect the piston with rag stuffed into the caliper to stop it smashing into anything or flying away when it pops out, and MIND YOUR FINGERS! trust me on that bit haha!)

or some people have had good results by fitting a plain bolt into the hole where the hose would fit on, replacing the bleed nipple with a grease nipple & forcing it out with a grease gun (got to get all the grease out afterwards, but a lot more controlled than compressed air)

 

There are two problems with compressed air (which I have used before).

One is a problem that I avoided, though you might not be so lucky. Brake fluid and brake parts cleaner are petroleum products. Forcing compressed air into the caliper at pressures high enough to push out that piston can cause those gasses to combust.

That might be bad.

I have had very good luck with bleeding the brake system and using the caliper to push the piston out. It IS very messy, and it DOES use rather a lot of brake fluid. It also means you have to have a working master cylinder. But it works very well and doesn't require any more tools than you already need to rebuild the brakes. (I don't have a grease gun.)

The grease gun can be done with less mess and away from the bike. As mentioned, be sure you get all of the grease out. I might disassemble the caliper again after a while (next riding season?) and clean it out again, just to be sure. But I'm paranoid and would have just gone with the "use the master cylinder" method in the first place.

But you *probably* don't need to replace the caliper, and it isn't worth taking it to a shop unless you have some sentimental attachment to it or your initials etched into it or something.

 

Cheers for the replies. Bloke is there a reason why with the grease gun you do it through where the bleed nipple would go and not through where the brake line would go?? Just curious why?

Thanks

 

Basically for reasons of thread size, you're not likely to find a grease nipple that will fit the threads of the banjo bolt hole.

I'd not really considered the "dieseling" question with compressed air, personally I wouldn't expect it to be a problem since by compressed air I only mean the kind you'd get from a hobby compressor circa 100-110psi & there's no way you'd get even real diesel to ignite at that pressure without it being vapourised by an injector... & even then I doubt it...

 

So I got it out air didn't work grease did. Now I have another question... Can I dip it in some chem dip? I no theres a plastic piece on the caliper and rubber which ill remove first. If so it might take off some paint. Any thoughts on painting the caliper.

Thanks again for the replies.

 

Clean it with brake cleaner. No reason to dip it in anything.

Brake fluid is very hard on paint. It'll wash anything from a spray can right off. You need to use a 2 part paint to have any chance of it staying on.

 

Degrease first then Etch it with an etch prime and use a 2 pack/part top coat as per MiCarl, brake fluid is a bit like paint stripper on single pack coatings.

 

The "grease gun trick" works when compressed air won't, as you discovered.

The bleed screw has an end that is similar enough to a Zerk fitting so that most grease guns can simply hook up.

The banjo bolt hole is also a common size so finding a plain bolt to pop in there is easy.

I repainted my caliper with Duplicolor "brake and caliper paint" and it's holding up very well; however you do need to be careful as brake fluid will indeed damage it almost immediately.

You also need to separate your caliper from its holding block, and clean the bores, sliding pin, etc. I would recommend replacing the sliding pin. Chacal now carries new caliper pin boots if the little rubber boots on your holding block are toast.

Here is a corrected and properly labeled exploded view of the 550 caliper; while this is a RH caliper yours is simply a mirror image:




When rebuilding the caliper, the single most important thing is to get the channels that the piston seals go in CLEAN. A "kiss" from a propane torch flame will turn any baked-in brake fluid mud to much more easily removable crumbly dust.

You can use a tiny brass wire brush in your Dremel, and/or sharpen up a couple of kitchen bamboo skewers to make channel-cleaning tools. You do not want to scratch or gouge the channels in the process of cleaning them.

 

thanks for the replies everyone. I thought that i'd share this with everyone... and if you haven't changed your caliper seals. checked your lines or rebuilt the M/C then check it out. I havent had time to visit the M/C yet but i have sent a pm to chacal for the parts. My brake line says (i think 10/81. not good) So its time to do everything. But these are the pads and seals. And im not proud of this but i'm glad that it is being taken care of...

Cheers to all

 

yowzer, how are your rotors??

 

Not toooo bad.

I was wondering if anyone nows how the M/C brake light switch comes off? Is it just the little tabs then pull apart the conectors. Wasn't sure.

 

http://www.xjbikes.com/Forums/viewtopic/t=34244.html

 

Thanks. That took about 2 seconds to remove. Lol

 

Are those caliper piston seals made of gold ????

 

How about encrusted with dried yellowish old brake fluid crud?