My KDX's front brake is "Weak"

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AZRickD
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Post by AZRickD »

Aha... I think I fixed it.

My solution? I did everything people said in this thread...at the same time.

Teflon tape for the nublette
Syringe on the caliper
Turkey baster on the master cylinder reservoir
Two C-clamps on the brake pistons
Screwed in the brake lever adjuster all the way in

With the adjuster screw all the way in, I was able to pump much more fluid through the system, which saved me time and bolt tigthening cycles, (but is too much for me to use while riding because the tip of the brake lever is all the way to the bark buster).

I found a technique that seemed to liberate bubbles in the reservoir that eluded me before. I would push on the syringe, and then pump the brake lever. Not bad -- then I stumbled upon an epiphany...

I was pumping away when I noticed something. No matter how much I pushed on the syringe (which would ooze micro-bubbles into the reservoir; and no matter how much I pumped on the brake lever or pushed the syringe, there would always be some micro bubbles coming out of one of the ends. Lots of micro bubbles. :supz:

It dawned on me that I maybe I didn't have air in my line, but air trapped in the terminal ends of the system. What I did was to start with an empty syringe and a full (and repeatedly re-filling) reservoir and pump the brake handle until nearly all of the fluid was out of the reservoir. This would begin to fill up the syringe. I would use the turkey baster to re-fill the reservoir and continue pumping. All the while the bleed screw was left full open with the syringed connected to it via a Home Depot tube. I went through several cycles when the micro bubbles stopped being expelled from the caliper end.

Heck. It was old fluid, so I dumped the syringe and filled it with new DOT 3. Then I slowly pushed the syringe to pump the fluid back up to the master cylinder reservoir (using the turkey baster to remove the excess). I found another technique that seemed to liberate even more micro bubbles from the master cylinder. I would push-pump-push-pump-push-pump little amounts of fluid back and forth. Kind of like a mini tug-of-war between fleas... only instead of pulling, I was pushing.

Nearly each time I pumped the brake lever, more micro bubbles trickled out the hole...

...until there were no more.

I tightened the bleed screw and undid the C-clamps on the caliber and bolted it all together. I was going to give it a test roll and brake in the garage when I remembered that the caliper piston was compressed and would likely need a few reservoirs full of DOT-3 fluid to extend. I was right. I pumped it up and after two or so re-fills, found that there was actually pressure building up (resistance in the lever).

I buttoned up the reservoir lid again and pushed the bike down the driveway and slammed the front brake. It squealed to a stop.

I then started up the bike and ran it down the road testing the brakes. It was nice to see my front forks compress under the braking load. Something I had seen with the squishy KDX forks, but had not experienced with the new KX forks. On my last run I grabbed a handful of front brake and felt the rear wheel lift off the ground (my first near-stoppee).

My work here is done. :partyman:

Rick
Last edited by AZRickD on 12:34 am Dec 08 2006, edited 1 time in total.
I done KX-ed QuailChaser's KDX220R
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Colorado Mike
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Post by Colorado Mike »

Sweet! The observation of "micro-bubbles" leads me to wonder if you encountered an extreme braking scenario wherein your brake fluid boiled. I have encountered this to a more spectacular degree. Nothing short of removing ALL of the victimized brake fluid restored the brake action (all 1.2 mouthfulls of it).

I went to a higher boiling point fluid since I sometimes ride at near 14,000'.
Mike

Life's tough, it's even tougher if you're stupid.
'04 KDX220
AZRickD
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Post by AZRickD »

C-Mike. I had bled both my rear and front brake systems previously (but not as thoroughly) and had not seen the micro bubbles before. However, I didn't see the micro bubbles until I did my multi-faceted technique, including both slow, and somewhat rapid, brake lever pumping.

I did do a rather long (couple of thousand foot) descent down a jeep road, but that was after my brakes were not doing well.

I can't speculate any further.

Rick
I done KX-ed QuailChaser's KDX220R
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thebleakness
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Post by thebleakness »

My front brakes work damn well. I was riding with some expert MX riders yesterday and they were teaching me stoppies. I managed to get acouple good ones in and thats with stock KDX forks. Squishy Squishy... :D
KillDozer
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Post by KillDozer »

Hi, just a suggestion. I was changing wheel bearings on my front wheel the other day, and when I reassembled the wheel my brakes weren't working correctly. Thought maybe they needed to be bled etc. Turned out when I reinstalled front wheel one of the brake pads moved slightly out of alignment on caliper. Had the same symptoms you were describing.
AZRickD
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Post by AZRickD »

A quick update.

The front break was working fine and then I noticed a little bit of a fade.

I did the bottom-to-top bleed routine (without doing the caliper as I was in a rush to go ride). Had a bit of the micro bubbles but not nearly as much as before. Then I noticed that my front brake lever adjuster lock nut was loose (and so was the adjuster screw).

Tightening that up, um, helped too.

Rick
I done KX-ed QuailChaser's KDX220R
Sky.A
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Post by Sky.A »

what model mighty-vac do you have?
Kauai Boy 04 kdx 200
AZRickD
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Post by AZRickD »

I bought a syringe at a Super Walmart grocery store. I bought some tubing from Home Depot and used some heat shrink to firm it up and then tied some stout thread around it to keep it solid.

Wily E. Coyote School of Motorcycle Maintenance.

So simple, even a...

Rick
I done KX-ed QuailChaser's KDX220R
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