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Discussion Starter · #1 ·
My xtr's are being replaced under warrant for sticky pistons (will arrive tomorrow), but they were out of pre-bled ones...so I need to fill/bleed them, and I'm thinking that it might be easier to do that before mounting them. Any tips or warnings?
 

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IPA Rider said:
My xtr's are being replaced under warrant for sticky pistons (will arrive tomorrow), but they were out of pre-bled ones...so I need to fill/bleed them, and I'm thinking that it might be easier to do that before mounting them. Any tips or warnings?
I have a set of Hayes Mags that I bled off the bike. I mounted the lever / master cylinder on a dowel and then held the dowel in a spare bike stand. I found It easier to obtain correct orientation of the master cylinder off the bike than it was on the bike.

I think it is important to make sure that the master cylinder / lever assembly be held in a stationary position by something, whether it be by the technique that I used, or by some other method.

The other advantage of filling / bleeding off the bike is that there is less chance to get brake fluid on some other part of your bike, especially the rotor. You do still have to take care to not get any fluid on the brake pads, but you can eliminate that worry by installing the pads after the filling & bleeding is finished.

That said, I normally bleed brakes on the bike. I was having problems with that particular brake and decided it was worth the extra hassle to take it off the bike to work on it.
 

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Discussion Starter · #3 ·
bleeding before mounting

Fixing the lever/reservoir was one of my main concerns too, but with that done, having ready access to and being able to see/manipulate both ends of the system at the same time seems like a good way to go
 

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I have a wooden block which has PM adaptor and length of handlebar attached to it; the block then goes in my bench vice and I have a handy, compact set-up for bleeding.

As Kevin has already pointed out, the main concern is keeping everything stationary. Although I use the set-up I described, I do so because I often get given brakes to work on and it saves me from having to fit them to one of my own bikes. By far the easiest way to get a safe, stationary 'workplace' is to simply fit the brake to the bike.
 

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IPA Rider said:
My xtr's are being replaced under warrant for sticky pistons (will arrive tomorrow), but they were out of pre-bled ones...so I need to fill/bleed them, and I'm thinking that it might be easier to do that before mounting them. Any tips or warnings?
I'm interested in the details of your sticky pistons. I have what I would call a sticky piston problem with my XTR's every few rides, and am curious to hear what yours were like. Thanks.
 

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Discussion Starter · #7 ·
XTR pistons

avam said:
I'm interested in the details of your sticky pistons. I have what I would call a sticky piston problem with my XTR's every few rides, and am curious to hear what yours were like. Thanks.
Same stuff I've read about being a pretty common problem with others...after not much use or build up of gunk, the pistons don't retract fully and thus the pads rub on the rotor. That means the pistons need to be serviced (clean, lube, and worked in and out of the caliper until its working well again)...and then a half dozen rides later (or less), same deal. After a while it gets worse and I finally got motivated to have them replaced. And this is under pretty friendly conditions of use (no mud and moderate dust and mileage).

I've had the rear replaced twice, the front, once...both under warranty with a good response from Shimano. Too bad they can't muster something that doesn't require so much hassle.

I've posted threads asking about piston retraction, and what makes this an issue with the XTR and other brakes, but didn't get much of a response. I'd really like to see more analysis of this aspect of the performance of all the top XC brakes (rather than just talking about weight, power, and modulation).
 

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IPA Rider said:
...after not much use or build up of gunk, the pistons don't retract fully and thus the pads rub on the rotor. That means the pistons need to be serviced (clean, lube, and worked in and out of the caliper until its working well again)...and then a half dozen rides later (or less), same deal. After a while it gets worse and I finally got motivated to have them replaced. And this is under pretty friendly conditions of use (no mud and moderate dust and mileage).
I always figured that the problem was due to one of the pistons being slightly looser than the other. (One piston will always be looser than the other.) The looser piston will always move (the most) first and make contact with the rotor first. Over time, the rotor may even begin to bend a little before the other, tighter piston makes rotor contact. If this should happen, the looser piston will not retract as far as it normally would. Once that happens, you might start to get some rubbing. Even if you don't, one pad will now be closer to the rotor than the other. When my Hayes got too far out of whack, I'd pull the pads, push the pistons back into their bores, and let the process start all over again. (I've switched to using BB7s and have been very, very happy.)

Anyway, that's the explanation that I came up with. But your analysis may be correct too.
 

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SteveUK said:
I have a wooden block which has PM adaptor and length of handlebar attached to it; the block then goes in my bench vice and I have a handy, compact set-up for bleeding.

As Kevin has already pointed out, the main concern is keeping everything stationary. Although I use the set-up I described, I do so because I often get given brakes to work on and it saves me from having to fit them to one of my own bikes. By far the easiest way to get a safe, stationary 'workplace' is to simply fit the brake to the bike.
Picture? I hope to get some hydraulic discs soon and I don't really trust the factory pre-bleed and I'll probably want custom length hoses, so I'll need to bleed them myself.
 
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