Another Dragging rear brake

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Codis8
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Another Dragging rear brake

Post by Codis8 »

Hello all, new to the forum. Recently moved to Colorado and got my 82 CBX back on the road.I have used the search function and cannot find the answer to my problem. I bought this bike 2 years ago with a dragging rear brake. The PO had been riding the bike this way for who knows how long. The pads and rear disc were toast. I stopped riding the bike until recently when i decided to fix it. Over the past month I have replaced the pistons, pads, caliper seals and disc. I also thoroughly cleaned the rear master using a dremel wire wheel and a dental pick. The little hole is not clogged. I am out of ideas. It still drags to the point where I cant touch the disc after about 4 blocks. Is there some alignment that could be off? I also bent the pad spring back to make sure to was not causing the pads to bind on the pins. On the 750f forum I read about the thick paint on new pads causing drag. Any one had this problem? I am out of ideas and summer is going fast. Thanks

mhutton
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Re: Another Dragging rear brake

Post by mhutton »

the pistons/pads retreat from the discs as the caliper seals recover their shape when the brakes are released. If this isnt happening the brakes will drag. Check condition of the caliper internals. No dirt or corrosion anywhere & the seal grooves properly clean. The seals should be replaced. Also there are 2 holes in the master, the fluid return hole is really tiny & sometimes overlooked. Clean it with a single wire from a wirebrush. If all this is OK the brakes will release properly unless there is some major issue with alignment. Read this too. viewtopic.php?f=50&t=7715

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Goss
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Re: Another Dragging rear brake

Post by Goss »

Hello Codis8,

I would unbolt the rear caliper and hold it by hand on the disk whilst applying the rear brake, when released the pads should only have slight resistance on the disk. What I am suggesting is eliminating the binding from the bracket/mounting.

If you have no binding using the above process then it is likely that the caliper mounting bolts are seized up, best way to check is remove caliper and slide them in and out.

Good luck and let us know how you get on.

Regards

Goss
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mhutton
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Re: Another Dragging rear brake

Post by mhutton »

one more thing. Is the master returning all the way? If not it may be holding the brake on. It needs to reach the end of its travel in order for the fluid to flow back from the caliper as the pistons relax.

Codis8
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Re: Another Dragging rear brake

Post by Codis8 »

I will remove the caliper and see how it returns when not bolted to bracket. Both master holes are clean. I completely disassembled the master. Maybe someone put the wrong master cylinder kit in? I will have to see if I can tell how far back the piston inside it is returning. As I said, this bike had been ridden a long time with binding rear brakes. Thanks for all the replies. I had read that other post.

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Re: Another Dragging rear brake

Post by SteveG »

Another possibility not mentioned is that the brake line/hose itself could be bad. It can "collapse" on the inside, allowing pressure to be pushed through (applying the brakes), but then not allow the pressure to go back into the master cylinder, leaving the brakes dragging.

If your piston seal grooves are cleaned out with the correct seals, and your master return hole is opened, and the master is properly assembled, I would look at the line.

Steve
82 CBX, 82 CB900F Project, 81 CB900(985)F, 79 CB750(810)F, 06 Wee-Strom

steve murdoch icoa #5322
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Re: Another Dragging rear brake

Post by steve murdoch icoa #5322 »

Hi ya, Codis.
If it was dragging before and after a complete rebuild i would be checking that all the axle spacers are positioned correctly.
Having seen lots of pics of the beautiful scenery in Colorado i would be itching to get it fixed as well.

Codis8
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Re: Another Dragging rear brake

Post by Codis8 »

Checked the caliper while not bolted the mounting bracket. It really seems to still be dragging. Everything really seems to be fine. The brake line idea sounds pretty good to me, I don't know what else to try unless PO put in an incorrect part in the master cylinder. Master seems to function fine however.

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Re: Another Dragging rear brake

Post by NobleHops »

Codis8 did you see my post? I had the same issue and in my case it WAS a plugged return orifice. Did you disassemble the master and pass a wire through the teeny hole? Clean it all out scrupulously, rebuild and and flush/bleed all the fluid?

Re your question about thick paint on the pad edges, I DID have a set that were a little thick on the edge and they did bind a tad on the edge of the caliper. I knocked the backing plate back 1/16 with a file and put a thin smear of antiseize on the edge.

One other thing to check that you did not mention: The sliding pins might need cleaning and lubrication, but for this you're going to have to unbolt the caliper halves and take them all the way apart. Clean it all within an inch of its life and lube the pins with high temp brake lube and reassemble. The action from my freshly cleaned and lubed caliper was downright springy - there's a bit of an air spring in there with the booties sealing it up.

Can you tell my brakes were a pain in the ass too?

N.
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Codis8
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Re: Another Dragging rear brake

Post by Codis8 »

The teeny hole is very clean. Disassembled The master completely and cleaned with dremel brush. Bought a new expensive brake line today and put it on but too much traffic right now to test it. I did lube the pins and they seen really smooth. Hope its fixed.

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