85R Rear Brakes Problems...Please Help

[Onetrackmind]

Ok... I realize that I've been on here less than 2 months and have already asked a ton of newbie questions (thanks for all the help by the way:p), but I have to ask for more help. My 85R rear brakes are killing me!

I just rebuilt the rear caliper (per the shop manual) and put in new pads. I took it for a short spin this morning to test out the carb rebuild (see my other thread) and when I got off to roll the bike in the garage, I could barely move it and the rotor was burning hot. It was doing this before which is why I decided to rebuild the caliper.

During the caliper rebuild when I was reinstalling the pistons, they were pretty darn hard to get in (yes I lubed them w fluid) and it surprised me at how much force was needed to push them all the way in...maybe they aren't all the way in? I cleaned the pistons and cylinders and tried to clean out the grooves for the seals as best I could. Maybe I left enough grime in the grooves to make the seals stick out too far?

The reservoir is not too full and the system is fully bled (I think).

I basically have zero clearance between the pads and the rotor even when cold and I know that's not right. What should my next step be?

Thanks, as always.

[atc007]

Your slide pins are dirty/rusty/hanging up.Remove them, clean and shine them, clean out the caliper where they live. Grease them ,install new rubbers and she'll work like new.

[Onetrackmind]

Thanks
New pad pin bolts came with the rebuild kit from Moose. I will pull them out and grease them...hopefully that fixes it.

On the pistons: with fluid in the system, how hard should it be to push the pistons in? I had to bleed the system to compress them far enough to change the pads.

[bobr]

Ok... I realize that I've been on here less than 2 months and have already asked a ton of newbie questions (thanks for all the help by the way:p), but I have to ask for more help. My 85R rear brakes are killing me!

I just rebuilt the rear caliper (per the shop manual) and put in new pads. I took it for a short spin this morning to test out the carb rebuild (see my other thread) and when I got off to roll the bike in the garage, I could barely move it and the rotor was burning hot. It was doing this before which is why I decided to rebuild the caliper.

During the caliper rebuild when I was reinstalling the pistons, they were pretty darn hard to get in (yes I lubed them w fluid) and it surprised me at how much force was needed to push them all the way in...maybe they aren't all the way in? I cleaned the pistons and cylinders and tried to clean out the grooves for the seals as best I could. Maybe I left enough grime in the grooves to make the seals stick out too far?

The reservoir is not too full and the system is fully bled (I think).

I basically have zero clearance between the pads and the rotor even when cold and I know that's not right. What should my next step be?

Thanks, as always.

I would remove the piston and seals again and clean out the seal grooves even more, as the least bit of corrosion will bind up the piston. Make sure it moves freely when it goes back in. Bob

[Onetrackmind]

Thanks. Unfortunately that's what I needed to hear and suspected might be the case. Those grooves were really full of gunk...and I probably missed some (it's kinda hard to see in there). About how far should the seals be out past the cylinder wall?

[atc007]

The grooves have to be empty,,spotless. If you think they aren't . Doing it twice :( Check your pins are perfectly free and smooth first..

[Onetrackmind]

Will do ATC...thanks.

Update tomorrow. (where's the "fingers crossed" emoticon?)

[KASEY]

the slide pins that the caliper runs on ,,NOT the pins that hold the pads in,,,, very important that they are smooth cleaned and greased

[onformula1]

Did you use a brake hone in the caliper bore?

[Onetrackmind]

Kasey
Thank you! It's 12:30 and I just read your reply after reinstalling the caliper that I rebuilt for the second time. This time I cleaned the crap out of the seal grooves...spotless and the cylinders and Pistons as well. It all went together so much better this time, but I could tell after filling and bleeding that I was going to have the same problem.

It was your reply that keyed me into the problem I think. Basically, I didn't understand how these caliper operates. The entire caliper is designed to slide in and out, as well as the Pistons. As pressure is applied, not only do the pistons force one pad towards the rotor, but it also PULLS the other pad towards it too...right? I slept through Disk brakes 101 obviously.

ATC, at the time I just did not understand what you were telling me. NOW...I think I do. Thank you!

I have had a had time mounting the caliper back on the bracket three times now and never realized that I never bothered to clean and lube the caliper pin or take out the collar that the mounting bolt goes through and clean and lube it either Now it all makes sense...this whole darn caliper is supposed to slide on the pin and inside the collar! Right? Dang...I feel like a complete idiot...wasted tons of time and now I have to wait till tomorrow afternoon to work on it again. I even had to pound on the collar to get the caliper to line up...geez.

Again, thanks to everyone...this has definitely been a learning experience. And Kasey, you said the magic words that made it all make sense...thank YOU !!!

[Onetrackmind]

So, I finally got the pin and collar off to clean them up and was amazed at the corrosion. The collar was so bad that I had to press it out with a vise and once it was out, it took a lot of soaking in CLR and scrubbing and polishing.

I got it all back together, lubed w silicone and it runs very smoothly. Thank you for helping me understand how it is supposed to operate!

I'm still trying to to diagnose a carb float issue (and we are having an ice storm), so I haven't test ridden it to see if this fixed the problem yet. It does seem to roll very smoothly now, but I have another question: I still don't have hardly any clearance between either pad and the rotor...not even my thinnest feeler guage will slip in. Is this normal? How much clearance should there be?
Thanks again.

[Marty]

Onetrackmind those sliding pins just replace them do not mess with used ones especially ones with corrosion!

[Onetrackmind]

My pin is corrosion free, but the collar on the rear of the caliper was really bad. I got all of the corrosion off, but it was left pitted. I polished it very well, but a new part would definitely be better. Thanks for the input...I just ordered a new collar.

[Red Rider]

...but I have another question: I still don't have hardly any clearance between either pad and the rotor...If you just put in new pads, and you still have a functioning parking brake system, most likely your parking brake is adjusted too tight now, causing the brakes to drag. Try backing the parking brake adjuster out to free up the brakes.

[Onetrackmind]

I made sure that the parking brake was not even touching the back of the piston...very loose. My pistons aren't flush with the wall of the caliper either...maybe 1/32"-1/16" out. It just seems that there isn't much room in the caliper for new pads, rotor and the shim.

I checked my front brake as well and can't get a feeler gauge between them either and it doesn't drag and get hot. So, how much clearance should I be looking for?

[Red Rider]

Are you running an OEM brake disc or aftermarket? If aftermarket, what is the thickness of it?

[Onetrackmind]

I'm not sure if it's the stock disk or not. It is measuring about 3mm thick though.

I put the old pads back on (which still had some life left in them) hoping that would solve the clearance issue and it looked good until I depressed the brake lever. The Pistons extended and did not fully retract. Is this now a master cylinder issue?

Also when I go to push the Pistons back in they move freely, but only one at a time. When I push one in, the other pops out the same distance. I'm not the sharpest knife, but I'm not dumb either...but this is making me feel like a complete idiot.

Thanks.

[Slingblade]

If you've got the system completely full of fluid, you will have to let off pressure. Crack the reservoir cap, bleed screw etc. Put an old brake pad accross both pistons and use a c-clamp or pliers.

It sounds like your caliper is working correctly. Like everyone said, the pins that let it float on the disc are almost always the culprit. I have destroyed good calipers trying to un-freeze them.

Let off pressure, push pistons in. Put in pads, bolt up caliper and bleed, then bleed again, and maybe again. Brake systems hate air.. Then I think you'll be good.

[Onetrackmind]

Thank you, thank you, thank you guys for all the help! I did just that right after my last post. I put it all back together and the pistons went right back to where they were.

So am I correct to assume that the natural resting position of the pistons is at the point where the pads are just BARELY touching the disk? Cuz that's where I'm at w either old or new pads.
Thanks again.

[Slingblade]

You are correct, sir. Very little travel on the pistons. The movement of the disc and the floating pins will create space while everything is turning, you know, when your ripping the snot out of it down some trail.. They don't always work perfectly while sitting still.

[Onetrackmind]

Awesome. I think I may actually be done with this brake then. Now...I can devote more time to the overflowing float bowl :-)

[Red Rider]

I'm not sure if it's the stock disk or not. It is measuring about 3mm thick though.

I put the old pads back on (which still had some life left in them) hoping that would solve the clearance issue and it looked good until I depressed the brake lever. The Pistons extended and did not fully retract. Also when I go to push the Pistons back in they move freely, but only one at a time. When I push one in, the other pops out the same distance.Your disc appears to be OEM, and it's thickness is not an issue. The pistons will never fully retract. If they did, you wouldn't get instant braking when applying the brakes with worn pads. When you push in on one piston, the brake fluid will take the path of least resistance, and push the other piston out.

Based on your last post, it sounds like you have them working properly now, with no more dragging?

[Onetrackmind]

As far as I know, there is no dragging. It doesn't sound or feel like it when I turn the wheels by hand. I think I'm good, but won't really know until I ride it.

I'm trying to figure out why my carb is overflowing even with a new needle valve. Will try to adjust the float tang a little and see if that fixes it. Might be able to test ride this evening.

Thanks again for the input.