Thread: Brake Caliper reassembly help sought

did you lube it prior to assembly?

if youve twisted the seal they get very tight. They also get very tight when the bore expands with corrosion.

Id suggest stripping them down, very lightly honing the bore of the calipers cleaning up then reassembling with fresh brake fluid.

Yes I put brake fluid over everything. I didn't think about cleaning up the bores - that is a good idea. They do not feel corroded to the touch, but they do feel a little 'rough'. Although looking at their finish, compared to the pistons, I always thought the pistons ran on the seal as opposed to the housing bores?

Thanks for that idea, it is a way forward!
Adrian

the seal provides the seal, the piston rubs on the bore as its not supported on both sides.

the forces of braking will slightly distort the pistons so they need to go back in the same holes with the same orientation.

just a small amount of "roughing" on the inside of the bore will cause the seal to "catch" and twist while its going in

Being a floating piston (moving assy), was it jammed on the piston or on the actual sliding pins. In the D2 thwese are often the culprit as the boots split and let in crap and corrode as well.

Which reminds me to get back to adapting some brembos to rectify my shortcomings of being able to stop better than it goes.

Good point about the sliders, they were free. And I find it hard to beleive that the pistons are matched to the caliper bore ( as suggested in the Haynes manual ) - in this day of accurate mass production!

Thanks for your replies.

Originally Posted by dusty disco

My front brake caliper (Disco D2a) was jammed - causing the brakes to drag. (The symptom was a rim so hot it was smoking after a journey of 10km)

I am trying to reassemble the calipers, using a genuine LR seal kit. I find that the piston is extremely reluctant to go back into the housing. The only way is to rubber-hammer it in! This does not seem right.

I notice the pistons all have some marks running in the direction of travel, although this has not resulted in any real roughness.

Is something not right here? I am thinking that the piston needs to be free-moving in order to prevent it permanently braking the wheel?

My vernier measures the pistons at dead on 45mm, and with somewhat less accuracy the seal inthe bore measures a bit less than that.

Is it possible that A.N.Other has used the wrong pistons?

Thanks
Adrian

Buy a tube of Brake Rubber grease, liberally coat the O-ring and the groove that it sits in, also the piston and the bore, make sure the bore is smooth and has no grooves, Regards Frank.

You need to measure the old seals against the new ones. We sand blast our caliper body's before reasambly and I probly wouldent use those pistons again chances are they will leak you can lightly polish them with very fine wet&dry with wd as a lubricant but from my experience with ap pistons the hard chrome is rubbish and just comes off and make sure you clean all the wd off the pistons before reasambly. Any brake shop can get you pistons if needed if you have trouble finding pistons pm me

I agree with ^^ don't reuse the pistons, they are cheap enough to replace them, IIRC a complete kit including seals and pistons is available.

The caliper bore is not supposed to 'interfere' with the piston surface, the piston 'floats' in the bore supported and sealed by the seal, even fluid pressure acting on the surfaces of the piston should keep it from rubbing on one side or the other of the caliper bore.


Seal kits are also avail through these guys or Rimmers. I can't tell on a weekend if our local suppliers can help the part number for piston is STC1918

http://www.lrseries.com/shop/product...E-CALIPER.html


JC