Front caliper leaking

[Steven May]

Ive been noticing some fluid leaking down and discoloring my front tire lately and realized my caliper is losing fluid. I had thought that it was from my forks which I had rebuilt, and I was mad about it. Now I just feel kinda stupid. Im going to pull off the offending caliper today, and see if I can understand what is happening. I've never rebuilt a caliper, and hope I dont tear something up. Any advice or warnings would be welcome, thanks

 

[Steven May]

No worries, pretty simple really. Took both calipers off and took them apart. Really dirty I guess they've been leaking for awhile...anyway, cleaned out the reservoir, and blew out the lines, cleaned up all the parts and the seals, put them back on and put new fluid in the system and bled them down...I guess we'll see if they leak again. The rubber seals were pretty dirty, you could feel grit on them which would create space for a leak I guess, so if it leaks again would they be the most likely culprit?

 

[Steven May]

I did not pull the pistons out. I put some channel locks on the piston and couldn't get it to budge, so I left it alone

 

[Pighuntingpuppy]

You need air pressure to pop the caliper pistons out. They dont slide out easy at all.

 

[Steven May]

Ok, so insert air pressure at the bleeder to pop out pistons? Looking at the pics I think maybe the leak is around the piston, so I will pull them back off and try this

 

[Fire-medic]

I've posted about this before, work on calipers.

From your description, they are in-need of a thorough disassembly. Though the factory service manual says, "don't split the halves," I have and will continue to. It makes it much-easier to clean them thoroughly.

I suggest a tool like a Dremel w/a wire disc of brass to-clean the groove in the caliper halves into-which the square rubber O-ring fits. Lube it thoroughly with brake fluid when you install the O-ring, then slide-in the cleaned piston. You should easily be able to move the piston in-and-out with finger-pressure. Your saying that you couldn't get the pistons to move with channel-locks means they're 'way-overdue for a disassembly and cleaning. You probably have one or-more frozen pistons, and a loss of braking function!

Wear eye protection when you use whatever brake spray you choose, I like Brakleen, it's not cheap, not trerribly-expensive and it does the job.

Yes the traditional method of using air pressure to pop-out pistons is good when it works, however, I've had to do this when air pressure won't work: use a grease gun.

Open the bleeder nipple, a caliper mounting screw fits the hose female in the caliper body. The piston will move. Use a C-clamp to limit the movement of one side when it's piston is freed, to allow the hydraulic pressure to free the other. Once they're both freed, split the caliper and thoroughly-clean the halves. I've never-encountered a bike caliper that wouldn't yield to this once air pressure alone was insufficient.

Some people say to use Scotchbrite pads to clean the pistons, I usually use a brass bristle brush and then something like 220 wet-or-dry for a final polish. Work-on the calipers until all-traces of corrosion are removed.

Here's a pic of a SOHC Honda 750-4 which was off the road since 1977 that I did awhile-ago, using the grease-gun disassembly. Once cleaned and reassembled, it functioned perfectly, the hose was replaced too.

 

[Steven May]

Thanks for the tips, fire medic. I will definitely follow your advice, and post again after, Appreciate the wisdom