Rear brake dragging after pad change - Curvy.

Hey guys,

Ive replaced the rear pads on my K2 rear calliper as they needed changing badly! I've changed the pads and put everything back together yestaday and went out for a 50 mile ride and the brake disc was really hot compared to the front disc's. When I was changing the pads, one of the pistons was hard to move compared to the other.

This morning, I got the pads off and gave everything a good clean. I pumped one of the pistons out abit and gave it a good clean with brake cleaner and a tooth brush, and then wacked some brake fluid on the piston to give it some lube, then I also gave the other piston a good clean aswel. I put everything back together, cleaned the pin and put some grease on the pin. Went to college this morning and the disc is really hot compared to the front. The pistons look like they have been corroded a little bit, I thought I would mention.

Is it normal for the disc to be really hot for a good few miles? Or am I going to pop the pistons out, give everything a good clean and every replace the seals? The pedal feels fine, the brake works well, I'm just puzzled.

Anyone shed some light please?

Thanks guys!

[andrewsmith]

Sounds like they are binding.

Get the caliper off and rebuild it, better to be safe than sorry

[jambo]

Well this all depends.

If you use a lot of back brake, especially in the last mile or so before you stop, it could just be that that's where the stopping force is working.

If in any doubt as to whether the pistons are dragging, I'd personally strip the caliper, clean everything up and rebuild it. I'd also be using red rubber grease, rather than brake fluid to lubricate everything, as things stay nicer for longer if you do that.

If you go for a ride and use no bake brake at all does it get warm? If you get the rear wheel in the air and turn it can you feel it dragging?

Jambo

Originally Posted by andrewsmith

Sounds like they are binding.

Get the caliper off and rebuild it, better to be safe than sorry

Thanks for getting back to me.

What is binding? Does it mean the pads are dragging slightly?

Cheers.

Originally Posted by jambo

Well this all depends.

If you use a lot of back brake, especially in the last mile or so before you stop, it could just be that that's where the stopping force is working.

If in any doubt as to whether the pistons are dragging, I'd personally strip the caliper, clean everything up and rebuild it. I'd also be using red rubber grease, rather than brake fluid to lubricate everything, as things stay nicer for longer if you do that.

If you go for a ride and use no bake brake at all does it get warm? If you get the rear wheel in the air and turn it can you feel it dragging?

Jambo

Thanks Jambo!

I only used the brake fluid as that's what I had at hand with me, I don't have any RRG, just used it to see if it fixes anything. I'm using the back brake a lot to bed in the pads. I won't use the back brake and see if it gets hot. I ain't got a paddock stand I'm afraid so have no idea how I could get the back end up in the air unfortuantly

Update guys!

I've gone home now and didn't touch the rear brake and the disc is slightly warm which is normal correct me if I'm wrong?

I can't seeing the disc being warped as it was fine before the pad change (despite the pads having hardly anything on them) and it didn't heat up.

When I was pumping the lever to get the pistons moving, I noticed that one of them was moving freely than the other. One of this pistons wasn't moving correctly, so I'm guessing this must be the problem?

Thanks for the help so far guys!

[jambo]

Originally Posted by Razer93

When I was pumping the lever to get the pistons moving, I noticed that one of them was moving freely than the other. One of this pistons wasn't moving correctly, so I'm guessing this must be the problem?

Thanks for the help so far guys!

I would guess so. Pistons out (one at a time if you can't split the caliper) clean up, red rubber grease on the seals and back together. Both pistons should move equally when all's well

Jambo

Cheers Jambo!

I've got 2 seal sets from wemoto and bought some castrol RRG off ebay.

How would I be able to get one piston out at a time? Use the brake lever to pump pistons out quite far, then disconnect brake line, pull/twist ONE piston out, clean up etc, new seals in with RRG, piston in with RRG, push back into calliper, then do the next one piston. After that's done, brake pads in, brake line attached, and refill and bleed the brake?

[garynortheast]

Push one piston all the way in and hold it while pumping the other one out.

[jambo]

Gary's on the money here.
The easiest way to do this is check that the calliper half joining bolts move (6mm Allen head) then take the pads out, pump the pistons until they meet in the middle, then split the calliper and re build. However if the calliper half bolts don't want to move you can push one piston back, pump the other out, clean up that calliper half and then re assemble. The down side it's that access isn't quite as good and you have to bleed the calliper twice (once after you've installed each cleaned piston)

Jambo