brake trouble...

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jafo
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Post by jafo »

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crazybrit wrote:>|<>QBB<
jafo wrote:>|<>QBB<
scheckaet wrote::hmm: 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
It was one of those things where you think your clear until it gets yah. It clipped the tip of my finger, so I was almost clear and yes I did read the warning but hey, sometimes you just have one of those days. I could'nt been clear across the room and it still would got me, shot my eye out or something. :rolleyes:

The pistons are not suppose to retract back into the caliper very much. They should keep a small amount of pressure on the rotor until you apply more pressure to them through the mastercylinder. It's kind of like holding a piece of paper with your fingertips and apply pressure and letting off without dropping the paper. Thats the best I can describe it. I'd start with the master cylinder and go from there if it were me. At least thats what I've done. as far as using abrsive paper, I personaly don't think it'll work but if the pistons are bad anyways what the heck. It's just time your spending. The reason I did'nt try the sandpaper was because to get all the bad area out of my pistons, I would have to take off a good amount of material and would have wound up making the piston out of round or no longer fit the caliper. Plus I don't like to band aid something like brakes especialy on an off-road bike. I'd rather spend the extra cash and put in new parts so I won't have to tear it down sooner than later, or wind up in the hospital from brake failure. Your call though, thats just my take on it. I'm sure it's stuff you've already thought through anyways.

As far as the piston popping back into the caliper, that wierd. I would say that might cause a mushy feel in the brake. Mainly because if the one psiton is popping back into the caliper, it has to be letting off some pressure I would think. I've never seen a caliper piston do what your talking about. Is there fluid leaking out around that piston?
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scheckaet
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Post by scheckaet »

Thanks for all the great replies.
Last night, i removed the brake pads and applied pressure on the break to see if the pistons were coming out.
One would, the other wouldn't unless I applied pressure on the other one. The thing is, I could see the piston retract a bit (might actually be normal cuz it makes sense) when I would release the brake.
I sprayed WD 40 around them to clean them up (lots of sand and mud) and will check them tonight. if it's still the same, I'll probably remove and clean everything good inside out (I promise I will definitely watch my fingers :wink: )
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Post by KDXer »

Maybe get some of these... :rolleyes:

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Post by canyncarvr »

Re: 'One would, the other wouldn't unless I applied pressure on the other one'

Did you expect something different? It's not like there is a differential circuit in there somewheres.........:wink:

I'm saying that is normal.

Most disc brake pistons do have some retraction device..usually the seal between the piston and the caliper. Retraction is not the primary purpose of the seal.

The most common reason for pads to hang up and not return (and they wear funny) is bad/dirty pins.

...that not having anything to do with anything..........except that it occurred to me. :roll:

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scheckaet
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Post by scheckaet »

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KDXer wrote:Maybe get some of these... :rolleyes:

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Your next pair of riding gloves maybe? :mrgreen:
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canyncarvr
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Post by canyncarvr »

KayD is looking to start his prostate exams early....wants to bring the doc his very own speshul gloves........

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Post by KDXer »

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canyncarvr wrote:KayD is looking to start his prostate exams early....wants to bring the doc his very own speshul gloves........
Yes your right, thanks again for putting me onto the great idea but since its that time of year I better send yours back. :blink: :lol:
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scheckaet
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Post by scheckaet »

:shock: I'll tell you what, those pistons can sure fly! Almost popped the windshield of my car across the garage :blink:
I'm glad I found my speshul glove though :lol:
I cleaned and inspected everything, the seal looks good and now I can't get the dang thing back in :evil:
Try again 2night, got to have it working for 2morrow's ride :?
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scheckaet
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Post by scheckaet »

I put everything back on, bled them, wait 30 min bled again, over and over till no air. I even moved the line, sake it and suspended the master cylinder so that the air could come out easy.
It gets harder, but still mushy :roll:
So now what??? This is driving me nuts :rolleyes:
I'll try a master cylinder rebuild kit, hopefully, the local has one for 2morrow.
Wish me luck
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Post by KDXer »

Zip-tie the lever to the bars overnight. It helps the air bubbles rise the the master cylinder apparently. Are you back bleeding ?? IE using a syringe and hose to force the fluid up from the caliper to master cylinder. This was the only way I could get an XR to bleed properly.

1. Draw with the syringe most of the fluid from your M/C leaving just enough fluid to cover the bottom outlet inside the M/C
2. Fill the syringe and hose with fluid, put the hose on the nipple (making sure you have no air bubbles)
3. Crack the nipple and force the fluid up into the M/C at the same time making sure not to overflow the M/C (another set of eyes helping is easist), close the nipple and repeat from step 1. until you have brakes again.

Takes usually 2 master cylinders full (or 2 cycles) of the above steps to get the XR bled.

FTR aquarium hose works well but goes milky a few days after sitting with brake fluid residue so its only good for one use really. Syringe I got from a vet.

Good luck.....
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scheckaet
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Post by scheckaet »

I pretty much did the way you described Trev (1 time only) so I'll give it another shot.
I stopped by the stealership before ridding. they want 200$ to fix it :shock: :mad: :evil: . The master cylinder rebuild kit is 35$, the 2 pistons and 4 stupid little rings is 130!!! Might as well get some new brakes :roll:
The guy said I might have an air leak around the piston, but I don't quite belive it cuz if I had a leak there, my brakes would be hard at some point and THEN get mushy, which isn't the case, they're mushy all the time so I WANT to believe it's the master cylinder. I'll try that 1st, in the meantime I'll be looking for a set on ebay...
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Post by Colorado Mike »

If you get one air bubble in your fluid, your brakes are mushy all the time. A bad seal can let air in, and it may also not allow pressure to build. Before spending a ridiculous amount of money on rebuild parts, I would buy late model parts off of ebay, but that's just me. If you choose to rebuild yours, you might look into aftermarket sources. they could be a quarter of the price.
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Post by TWMOODY »

Make your life easier and unbolt the caliper compress the piston most of
the way and stuff a small block of wood between the pads.
Hold the caliper as far up as you can in a position that the bleed screw
is the highest point of the assy then use a mighty vac or manually
bleed the system.
Doing it this way you are not trying to push or suck air down.
If you are manually bleeding pump the brake a few times with the
bleeder closed then while holding the brake, crack the bleeder
and close it right before your handle hits the bar.
Repeat until you got some brakes......
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scheckaet
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Post by scheckaet »

thought I'd give an update on that old post.
Well this week end I FINALLY solved the problem. After tearing the brake completly cleaning them, bleeding I don't know how many time, I still could not figure out WHY it was still so "mushy" and ineffective.
So I tried the "Mac Guyver" solution and the repair was ... well REALLY expensive... : 53 cents. :blink:
The only problem with the brake was the lever adjuster. :roll: .
I thought I should try a longer one and see if the brake would be better. Bingo, a trip to the hardware store was all it took, now I have some brake!!!
What I thought were mushy brake were in fact the brake being really progressive :roll: , the lever was just not adjusted properly.
That is really nice and I can do stoppies much much easier now :mrgreen:
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