KDXRIDER.NET

So this problem developed kind of out of nowhere!

When we rear brake heats up, it sticks. As soon as it cools down again it's fine. What is the deal? I'm burning through the pads like there is no tomorrow and i'm not really using them too much.

I pulled the caliper, pulled the piston out and cleaned it, i lubed the pins. It still has the same problem. I was just looking at the fiche and I am missing a part. If you're looking at the fiche http://fiche.ronayers.com/Index.cfm/Mod ... Rear_Brake

it's part number 32085. I have no idea where it went. I didn't even know there was one there until just a few mins ago when i looked at the fiche. Could this be why it's sticking?

Just as an FYI, i can't push the piston in (even after a cleaning) with a c-clamp unless there is no fluid. When it's fluid filled and air free the piston will not compress.

Just another FYI. This morning when i took it apart i didn't know i had to grease the pins that hold in the pads. I went out and tested it this afternoon and they were still sticking after they heated up.

I came home looked at the manual again and realized those were supposed to be greased up, i've now greased them up, any chance this is the problem??

Again keep in mind that i cannot push the piston back in with a c-clamp if there is fluid in the line...

the seal should allow enough spring back to get the pad off the rotor. That's not a lot of space, certainly less than what a clamp is gonna give you. you say you got the puck out and cleaned it. So I take that to mean it wasn't seized in there. No rust in the body or on the puck? Typically, they rust and seize up. well, not typically all the time, I mean when one won't move anymore.

Will the piston go in using a clamp, with the master cylinder cap off?

It actually sounds like a Master Cylinder issue, not a caliper problem.
You should be able to push the puck into the caliper with a clamp and the fluid goes back into the MC.

Rick wrote:Will the piston go in using a clamp, with the master cylinder cap off?

Nope :( Master cylinder is the resevoir by the back brake pedal right? Yeah i pulled the cap off and it still wouldn't budge!


The piston without pads in moves freely when you pump the brake. And with no fluid in the line goes back in the caliper no problem...

WD40
Maybe a Rear Master Cylinder Rebuild??

bike is only on it's 3rd rear tire, 2nd front tire, mileage is low. I doubt it would need a rebuild!

maybe not a rebuild, but a good WD 40 cleaning is cheap and easy

how do i do that?

Can someone show me a pic of the master cylinder?

Some of us (me) would appreciate plainly stating what bike you're talking about. I'd rather not assume..and don't want to go looking..even if it's only as far as in the text of the URL you posted.

Do the pins have any wear on them at all? ..divots where they pads have rubbed? IF they do, it's time to replace them. Yes...I realize that has nothing to do with the piston not going back in..but 'Fix what you know is broke' is a good tack to take in such a case (a 'What's going on?' case). Be sure to put anti-seize on the pin threads!!


Re: 'The piston without pads in moves freely when you pump the brake.'

Does that mean 'out' only? 'Moves freely' means, well...moves freely..and that includes into and out of.

Are you using a clamp directly against the piston, or using a block to distribute the pressure? Sideways pressure (crooked at all) may keep the piston from moving with the slight added resistance of fluid.

BTW...what kind of fluid did you use?

While you're trying to move the piston back into its bore, what is the position of the brake pedal? If it's 'down', there isn't going to be any release path for fluid. Hadn't better be, 'eh? What kind of brake system would that be?

With some pressure on the puck (and it being in the 'stuck' condition)..loosen the bleed. Pressure drops? Fluid comes out? It's not a piston/caliper problem.

If the activating rod for the MC is completely released..there is a pathway for fluid to AND from the MC res to the pressurized side (line/caliper). If you take the brake pedal off (free the rod) you can tell if the MC piston is where it should be by feel. There shouldn't be any 'gap' between the activating rod and the MC piston (what the rod pushes against).

I don't think you will find a diagram of the rear MC. I don't know that it's rebuildable.

**edit** Yes it is. Look at callout 43020 on the fiche. On the BuyKaw fiche anyway. That should do for a diagram, right? Take it apart if none of the other stuff in this post (like pedal being 'down') applies. **edit**

If you're using a pressure bleeder, try just that..use pressure, not vacuum to bleed the brake system. Push fluid from the caliper to the MC. If you cannot move fluid that direction (again..the MC piston has to be 'out' of its bore..released..not pushed in), there IS an obstruction in the MC.

Not all bleeders have a pressure capability. Mine 'fer instance. You could use a syringe to try it.

Oh...if you're cleaning the MC..use BraKleen.

This is my 2001 kdx220. I will give your post a shot and post my results :)

Ok here's the deal.

i still can't push the piston back in when there is fluid in the system. When i put pressure on the piston with a clamp the brake pedal is stiff as a board. It has no travel. I'm sure that means there is some kind of a return port in the master cylinder that must be clogged right? Or maybe some kind of valve that supposed to work 2 ways but only works one...

So having said that, what can i do to fix this? I couldn't figure out how to take apart the MC.....

A couple of things (specifics are important...and matter..so please be specific):

When you put pressure on the piston the brake pedal becomes 'stiff as a board'?

..or was it that way BEFORE you put pressure on the piston?

You understand why that's an important distinction?

IF the pedal 'becomes' stiff (loads WITH pressure from the caliper piston as the piston is pushed on) AND the pedal is not preventing the MC piston from being pushed back to where it should be by the MC spring (due to misadjustment or maybe physical obstruction)..then the MC does have a problem.

WITH the MC piston at its normal 'at rest' place you should be pushing fluid into the MC res when you push on the caliper piston.


Along the line of 'be specific'... I asked what fluid you used and didn't get an answer.

Also...there is a parts diagram..did you look at it?



92022A is the clip that holds the guts of the MC IN the MC. What is there to figure out? ...or not?

Oh... the MC is NOT plumb full..and the diaphragm IS in place, correct?

My KX 250 '01 lost the rear brake power soon after I got it; piston was stock in place. Not surprisingly, the brake fluid was old and very very dirty. I did remove all the old brake fluid and realized that at the bottom of the brake reservoir there was gunk that looked just like mud. I did clean the reservoir, brake like making sure there were no dirt clogs anywere. Other thing that I did was to replace the brake pins since they were wore out as well. After that and bleeding the brakes, I have had no issues whatsoever whith the brakes.

Note: I did clean all the parts with regular brake cleaner from any auto store. Total work took me about 35 min.