KDXRIDER.NET

I can't get them to work!
In the last few rides I noticed it was getting a lot more "spongy". So I replaced the brake fluide with DOT 4 and bled them.
It took me FOREVER to get all the bubbles out (followed the procedure step by step...2 hours???) Still spongy, but hard enough to ride for the week end.
On the parking lot, asked my buddies for a hand, and bled them again (they have way more experience than I do but the problem remained )
Had to pump the break for like 20 min to get it working. They all said every time I put pressure on the breaks, the oil should squirt out of the bleeder (the reservoir should get empty with 3-4 pumps I was told), but it does not, it would only barely drip. They said maybe one of the seal inside was worn out.
So I got home and took apart the reservoir, and everything, gave it a good cleaning, checked all the "seals" everything looks ok.
Replaced the fluid, this time, I used a syringe and pushed the oil through the bleed screw and put everything back together, pumped a few times to remove the bubbles, put the cap on and ... you guessed it: nothing.
I can bring the lever all the way to the grip and it's very spongy / muchy. In other words NO GOOD

So my question is what the hell is going on? air in the system? (I replaced the fluid and bled them TWICE and I had others helping)
Am I missing something else?
What I find odd is that when I pump, the oil is not squirting out but only dripping. Is there anything else that I need to check/replace?

Sorry for the long post
Any input is appreciated

wilf

Note: I don't know if it matter or not but I used DOT 4 for cars (and tusk brake pads.) Needless to say a fancy vacubrakebleederthingy is in order.

try a rebuild kit for your Master Cylinder. I asked the local shop wht to do about my problematic brakes and a mechanic told me to rebuild the master cylinder. Piece of cake, I had no idea. The kit cost about $35 bucks, the rebuild took about 14 minutes and i gots fine brakes now .

Karl

KarlP wrote:try a rebuild kit for your Master Cylinder. I asked the local shop wht to do about my problematic brakes and a mechanic told me to rebuild the master cylinder. Piece of cake, I had no idea. The kit cost about $35 bucks, the rebuild took about 14 minutes and i gots fine brakes now .

Karl

Do you know what part was worn out?

I thought I read somewhere that air could get trapped in the KDX system due to how the hose/caliper arrangement and you needed to remove the caliper and hose and bleed it off the bike to get the air out. or maybe I'm thinking of one of my other bikes and some other list, downside of owning so many bikes.

I'd be interested in kits but I need a caliper kit. one of the two pistons I think is foobared, doesn't engage, with the pads out, it will move forward and then pop back. the other piston is fine, just keeps moving forward until it pops out.

I've bled it, taken the pistons out, seals look ok, bit of a mystery.

I still think only one piston of the two is working, feels mushy also.

I don't know what part was worn out. There is a piston, a spring, and two rubber seals in the kit. I just put it all in.
I think you are suposed to be using DOT 3 fluid, though. I could be wrong. I had best results with Kawa original brake fluid. Probably just a coincidence, though, because I had those best results after rebuilding the master.
I had no trouble getting all the air out. I run a hose from the bleeder to a coke bottle with a couple of inches of brake fluid in it submersing the end of the hose and pump away.

Karl

I think you are suposed to be using DOT 3 fluid, though

The manual said dot 3 or dot 4, so I went for the higher boiling point thinking it was part of the problem.

same thing happens to my bike. I normally have to sit and bleed the brakes for at least 20-30 minutes. Do you have one of those things that lets you bleed the brakes by yourself? (basically a tube with a check vavle)

Ryan wrote:same thing happens to my bike. I normally have to sit and bleed the brakes for at least 20-30 minutes. Do you have one of those things that lets you bleed the brakes by yourself? (basically a tube with a check vavle)

yep just installed them last w-e and the problem is still there

Just a thought for you guys using the "one man bleeder" -- give KarlP's method a try. I've used that method on newer cars, old cars (about 10 minutes for all 4 corners) and bikes with no trouble . If you can't get the air out that way, seems to me you're sucking air somewhere so the rebuild may be in order.

Are the lines in good shape??

With all humility, it's not my method. I read about it on a Porsche forum.
Just a clarification, while pumping the blead screw is open. I don't close it between pumps until I've got a steady stream of clean fluid. Three or four more pumps in the traditional manner and it is done.

SPEED BLEEDERS are the CHECK VALVE System you are talking about

I have a similar problem with my YZ250. I put in a master cylinder kit also thinking that would fix the problem. Did'nt. I put a new set of shoes on the front to see if that would help(needed them anyways). Thats when I found that one of the front caliper pistons was sticking out and not retracting back like it should. After taking a hard spill in the corner on the track I could'nt understand why the front end washed out with a new tire until I got home. The front rim would barely rotate because of the lockedup piston in the caliper. So thats my next little project as soon as I get around to ordering the seal and piston kit......$65 bucks!

Here's my diagnoses on what happened with the new pads. Basicaly the new pads being thicker, pushed the pistons back into the calipers where they should be. The pistons though have been beat up so much from the dirt and sand and riding out so far of the calipers so long now that it's made that area rough and making them stick on the seals with new pads installed. I put the old pads back on and it's rideable but not braking like it should.

I've always understood that a spongy feel in hydraulic brake systems was due to air being leftin or getting in the system. An that still might be the case. It only takes a few bubbles to do it. I'm thinking possibly that air is being sucked back into the caliper because of the piston/seal problem.

Jon.

Jon.

Interesting Jafo. Could be that too, I recently replaced the brakes... I will tear them down tonight and see what they look like.

KarlP wrote:With all humility, it's not my method. I read about it on a Porsche forum.
Just a clarification, while pumping the blead screw is open. I don't close it between pumps until I've got a steady stream of clean fluid. Three or four more pumps in the traditional manner and it is done.

By the way, your leaving the blead screw open after letting off the brake lever? Thats all wrong. If you do it without a vaccum system or one man system here's the propper way to bleed a hydraulic braking system at least like this one. First you pull the brake handle back slowly at first maybe four or five times and hold the handle in while you release the bleed screw. Before letting the brake lever back out, close the bleed screw. You need to do this everytime you go through a cycle. Every two cycles you need to pop the cap off the reseviuor and check the fluid level. Do not let the fluid level get to low or you'll have to start over. Only open the bleed screw when the lever is pulled in. thats the only time it should be open. By leaving the bleed screw open and pumping the lever, your pulling air back in through the bleed screw. Thats why they make the for-mentioned one man bleeders. They're like little check valves that keep the air out when you let of the lever.

If your pumping the lever with the bleed screw open, you defintley have air in the system.

All you have to do to see if the pistons are locked up is try to spin the front wheel. If it's free then thats not it.

scheckaet wrote: Interesting Jafo. Could be that too, I recently replaced the brakes... I will tear them down tonight and see what they look like.

Caution!!!!!! When working on calipers like these, be very very careful. It requires compressed air to get the pistons out of the caliper. Believe me when I say, they come out like bullets. So be careful and don't have your fingers in the way like I did. I had a heck of a blood blister when one shot out and pinched my finger. Thats why I say to try spinning the front rim first before going through all that trouble. Also try using a wash towel or some king of thin padding to protect the pistons from being chipped when they hit the outside part of the caliper. They are so tight in the seals that they build up pressure behind them before popping out.

I run a hose from the bleeder to a coke bottle with a couple of inches of brake fluid in it submersing the end of the hose and pump away.


KarlP wrote:
With all humility, it's not my method. I read about it on a Porsche forum.
Just a clarification, while pumping the blead screw is open. I don't close it between pumps until I've got a steady stream of clean fluid. Three or four more pumps in the traditional manner and it is done.

Works for me, I gots speecial breaks

Yeh that'll work. Just be sure that your hose is not leaking at the bleeder valve. I've had them fall off on me before. just some advice.

jafo wrote:

scheckaet wrote: Interesting Jafo. Could be that too, I recently replaced the brakes... I will tear them down tonight and see what they look like.

Caution!!!!!! When working on calipers like these, be very very careful. It requires compressed air to get the pistons out of the caliper. Believe me when I say, they come out like bullets. So be careful and don't have your fingers in the way like I did. I had a heck of a blood blister when one shot out and pinched my finger. Thats why I say to try spinning the front rim first before going through all that trouble. Also try using a wash towel or some king of thin padding to protect the pistons from being chipped when they hit the outside part of the caliper. They are so tight in the seals that they build up pressure behind them before popping out.

Did you read the service manual before you blew them out? There is a huge warning about keeping your fingers out of the way.

Easiest thing is to just push the pistons out using the brake lever. In my case one wouldn't budge so I had to use compressed air.It took over 40psi to force it out. This will crush your finger. Use a piece of plywood to soften the impact of the piston coming out, you need to use something (other than your finger) as you don't want it hitting the other side of the caliper.

Like I said 5 posts ago, mine are mushy and I think it is caused by one of the pistons binding. I've removed it, the seals look ok but it still happens. I was thinking of removing it again and gently smoothing it using some 800 or 1000 grit wet paper.

My wheel didn't have resistance when spinning it, the pad wasn't dragging, rather one of the pistons would just advance upon pressing the lever and then about 80% thru the lever stroke, it would pop back into the caliper body. The other piston was fine so I had poor braking power, uneven pad wear and mushy feel. Maybe the mushy feel is due to a problem elsewhere (master cylinder), dunno. Fix one thing at a time is always my view, so I figured both pistons should advance smoothy and until they do, I won't look elsewhere.

tony

Use the proper tool (akin to a MityVac), PUSH the fluid instead of PULL it.

Re: 'If your pumping the lever with the bleed screw open, you defintley have air in the system.'

Yep.

Unless you have the bleed hose stuck in a container that prohibits air from getting back up the line.

Doing it like that should take about 5,897,345,876,087 pumps...and a similar number of pints of brake fluid.

MityVac.