How to tell when your calipers need rebuilding?

Doing some replacement of parts for the XJ1100 and I'm wondering how to know if the calipers are working properly or are needing a rebuild?

Mine aren't leaking although one front brake grabs if the wheel is rotated and this was suggested to be the result crud in the MC spooge hole. If I remove the caliper to check it, I'm not sure what other than a leaking boot to look for that would tell me it's bad.

Idears?

 

One of the symptoms is that when you try to push the bike backwards it is VERY hard to push. The problem is that the calipers and pistons get corroded and then they don't release all the way. If one of your calipers is grabbing when you trun the wheel by hand it could be the master cylinder but I would not rule out the calipers. Rebuilding the calipers is easy - bleeding them is a pita.

 

You won't find any "boots" on your calipers (other than the little boots on the sliding pin.)

This isn't a car.

Your caliper consists of a hole with two channels around its bore. Two square-section rubber rings sit in the channels, one is the actual piston seal, the outer one is considered the "dust seal." The piston itself is nothing but a smooth stainless steel cylinder that slides in the seals. No boot, no real complexity.

What happens is over the years, dried brake fluid and/or corrosion builds up in the channels behind the seals, making it harder and harder for the piston to move freely. The first symptom is usually the "I can't roll the bike backwards" syndrome; it happened to me with my 550 when I first got it.

The most important thing here is those rubber rings that are the caliper seals. They're just rubber rings. 25+ year old rubber rings. That you stake your life on every time you grab the lever.

THEIR AGE is the single best reason to rebuild your brake caliper(s.)

 

Hi Fitz & Mirco,

No problem at all in rolling the bike backward.
If I push the bike straight ahead there's no issue.
If though I turn the wheel to the left and push, it binds up. To the right there's a tiny bit of forward restriction but to the left definitely has the most friction.

On the XJ1100 the left caliper and the rear caliper are linked together via a proportional valve. The right front is solely controlled by the right grip.

Rebuilding the calipers though sounds right thing to do. How do you express the piston out once the caliper is off the bike? Might be obvious when I get the calipers off but I'd like to be prepared & know what to do when I get there.

Thanks

 

If the brakes are dragging, chances are you need to rebuild the calipers as well as the M/C.

Easiest and safest way to remove the piston is to block the banjo union with a bolt, and attach your grease gun to the (open) bleed screw; then pump it full of grease and the piston will ease out. Yes, it's a tad messy; but I've never had any luck using compressed air.

 

What about if I remove all the calipers from the bike, remove the pads & then while they are all still attached to the brake lines, pump the brakes to pop out the piston?

Seeing as the right front caliper is the only one moved by the front MC, I could pop it completely by pumping (I will be replacing the lines at the same time)

I could then put a piece of wood inside the L front & rear caliper to stop the pistons from coming all the way out so by pumping the brake pedal they bulge enough to put a clamp on the pistons and then remove the bleeder screws fore & aft to remove the suction & then pull the pistons out?

Not sure I'd want to try removing all that grease from inside of 3 calipers using a grease gun to extract the pistons.

Does this sound like a good workable alternative?

Thanks

 

Sure. Messier yet, probably work.