'91 KDX250 Rear Breaks Grab/Lock

[xsnrg]

I ride a '91 KDX250 and my only complaint is that the rear brakes are extremely touchy and lock-up quickly, often stalling the engine (despite the heavy flywheel weight of the 250). Usually it is an issue mostly on long downhills with loose traction, but recently I tapped them on a slight uphill with some slick clay and the instant the breaks started catching, they immediately locked and stalled the engine.

I've searched the FAQ and read all the Search hits for Brakes on this forum...but I've yet to find a conclusive solution to this problem. Below I'll pull together most of the suggestions I've seen elsewhere and pose some questions. Please let me know which of the following suggestions you would try in order...

-> sand the pads
-> spray brake cleaner on the pads (may be contaminated)
-> replace the pads (with softer pads)
-> replace brake pins (scratched, damaged, corroded) with aftermarket pins. (and be careful not to strip or break during removal as many threads discuss).
-> bleed the lines using the many known methods
-> replace the brake fluid with a higher quality DOT 3/4 fluid, but not DOT 5 because it doesn't mix well
-> replace the caliper
-> Is there a complete swap option (KX, later model KDX, other brand/make, or aftermarket) that will upgrade to a better peforming brake (perhaps later technology)


Please order these steps to try to remendy this specific problem and propose any new ones or other inputs. If anyone successfully solved this issue, please tell what did the trick!

I am headed to the Hatfield-McCoy trails soon and don't want to tackle those hills without a fix!

Thanks!

 

[wibby]

Does it lock up right from the get go or does it take a little while, like after it gets heated up?

Does your wheel spin freely when you have the bike on a stand, or is the brake dragging some?

On a recent ride my front brake was completely locking up. Somebody?? :clue: had turned the adjuster all the way in?? Soon as we'd hit a fast section my bike would start to slow, eventually to a stop! I'd have to bleed it some and lots of little air bubbles would come out! Luckily we were riding in thick gravel, kinda unnerving to look down and see your front wheel not turning :eek:

 

[xsnrg]

Pretty much from the get-go, right off of the trailer. You press down on the rear brake lever and there is no gradual slowing, it just seizes and locks up until you let go of it. It doesn't stick on or anything, it releases just as quick as you let up.

It spins freely on the stand, that is how we oil our chains, one of us sprays while the other tips the bike up on the kickstand and spins the wheel.

 

[Dogz]

My 250 did the same thing 2 rides ago. The wheel side pad had worn right out, Had the rotor turned to clean it up and put in new pads, lubed the pins with brake grease. Back to perfect.
I also had some rear brake troubles last year but that was new stiff boots,couldn't feel the pedal!
Try readjusting your pedal, I find on any bike if the pedal is to high and you have to lift your toes to get on the pedal you lose braking feel.
My 250 locks up quite easy but with a properly adjusted pedal and broken in boots I love it. I pretty much just have to flex my foot down and I'm getting brakes. A little harder and you have lock up.
In comparison I have to stomp on the ninja and the drum in back of the RD is a weapon not a brake. I think thats why all Rd'ers do a stoppie at every light, to quick and the oh sh*t pedal don't work! i

 

[JasonWho]

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[tedkxkdx]

I am having a similar issue with a 96 front end I transferred to a 92. The brake assembly used to be fine but I have not used it for around three years. I changed the pads, pushed the pistons all the way back in and inspected scraped and copper greased the lower brake pin. I think the pistons are just coming out and not retracting. It sounds easy enough to take it apart to clean that area but a friend tells me to pump the pistons to the farthest out position and then push them back in and do that about ten times to get everything loose in there.

 

[xsnrg]

The pads were changed before last riding season, < 50 hrs of trail riding (not racing) total on them. The bolts were checked and the lines bled at that time also, but this is a condition that the bike has had even just after the pads were changed and has not changed noticeably since. I started riding the bike after that change, but the person that rode it before said the bike has always done it.

 

[JasonWho]

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[dirt bike dave]

Is the disc bent or warped? I had a '91 kdx250 and the rear brake worked fine.

 

[JasonWho]

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[wibby]

Also, if you don't have one already, get one of those vacuum brake bleeders

Sure makes it easier to get all the air out.

A little tip though: take the bleeder screw out and wrap it with teflon tape or you will suck air right though the threads!