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Big E
06-02-2004, 05:12 AM
Anybody know how I adjust the amount of pull on the brake lever for Shimano hydraulic discs (model sumthin-sumthin-525)? I thought my pads were just worn down and needing replacement, but I pulled them yesterday and they're fine, and when I pull the brake lever, one of the pads never contacts the rotor. It seems like the alignment of the rotor relative to the caliper is off, but it's in the opposite direction that those things are usually off, ie, there's no space between the rotor and caliper to the outside, and loads to the inside.

Anyone? Bueller?

snow_slider
06-02-2004, 06:11 AM
I'm not familiar with Shimano's disc brakes. Do they use shims for the caliper alignment like Hope, or not (like Hayes).

If they use shims, then you'll need to add or remove shims till both pads contact the rotor evenly.

If they are like Hayes, then just loosen the caliper bolts, squeeze the brake lever so the pads clamp down on the rotor, then (while maintaining firm pressure on the lever) tighten the caliper bolts. That should center the rotor between the pads. If not, you can repeat this proceedure, but insert a business card or other thin object between the rotor and pad on the appropriate side before squeezing the lever and retightening the bolts.

Big E
06-02-2004, 07:07 AM
They do use shims, but from my look yesterday, it seems like the shims would only work if the alignment was off in the "other" direction. Lets see how my ASCII art is...

......I
...._I
_ | |I
*|| |I
*|| |I
*|| |I
--|_|I
......I
......I

I'm a bike JONG and doing this from memory, so bear with me. Looking from the rear of the bike, the part with the ** is the mount on the frame of the bike, then the next rectangle is one side of the caliper, and then the vertical "I"s is the rotor. So, the problem is that the rotor is rubbing on the caliper on the side that mounts to the frame, but the shims I thing were designed to correct an alignment problem when there's too much space there.

I first noticed the soft rear brakes after a ride where I had a particularly noteworthy wreck - it was either me or the bike hitting that tree, and I chose the bike. The crash knocked the head tube loose, but I wonder if I somehow buggered something else up. Argh, really wanted to get out this weekend. Wonder how fast the shop could get it fixed up...

edit - Ack! Board automatically deletes spaces at the beginning of a new line. :mad: I put periods in as placeholders, *try* and ignore them (good luck).

mntlion
06-02-2004, 07:16 AM
When was the last time you had the brakes bled? might just be more fluid needed? minneral oil NOT DOT3

Like someone said, pull the wheel, squeeze the lever and reinstall the wheel, now with the pads closer?

What would happen if you removed some shims? rather than adding them?

onse the pads are closer then center them.

Crinkle
06-02-2004, 07:28 AM
check this link out http://bike.shimano.com/mtb/DeoreXT/componenttemplate.asp?partnumber=BR-M755

they have PDF files for servicing and exploded views of Shimano parts. Its a good resource, I didn't read any of it, but most likely you can find your info here.

altagirl
06-02-2004, 07:31 AM
I was also thinking bleeding the brakes might be a good place to start.

Big E
06-02-2004, 08:16 AM
Yeah, I'm wondering if bleeding is the problem too. I know I certainly did a bit on that crash :rolleyes:

Crinkle, yeah, I found that and was looking at it. Whatever the problem is, it must be in there. As usual, unless you're really familiar with it, hard to look at the diagram without having the bike sitting in front of you. And if you're that familiar, you probably don't need the diagram.

snow_slider
06-02-2004, 08:52 AM
If you can pull the lever and it doesn't feel overly stiff (hard to pull), then I would guess bleeding your brakes might not help. If you have too much fluid, then the first sign is that your lever doesn't have the travel it should and feels stiff to pull.

Try removing a shim from each caliper bolt. That should effectively position the caliper closer to the frame side and eliminate the rubbing.

altagirl
06-02-2004, 08:57 AM
Originally posted by snow_slider
If you can pull the lever and it doesn't feel overly stiff (hard to pull), then I would guess bleeding your brakes might not help. If you have too much fluid, then the first sign is that your lever doesn't have the travel it should and feels stiff to pull.


I'm confused. (maybe I'm just not reading this right) Every time I've needed to bleed brakes it's because they feel too squishy/spongy and pull in too far. You're bleeding air bubbles out of the lines and adding extra oil, not getting rid of excess oil...

Jiffy
06-02-2004, 09:13 AM
on my Hayes brakes the squishy feeling went away with alittle screw adjustment on the brake lever (small hex screw that attaches to the cable or whatever). i thought i would need to bleed also, but shop guys said nope.
you should also try snow sliders fix before getting more involved in the brake bleeding process

altagirl
06-02-2004, 09:20 AM
Originally posted by Jiffy
on my Hayes brakes the squishy feeling went away with alittle screw adjustment on the brake lever (small hex screw that attaches to the cable or whatever). i thought i would need to bleed also, but shop guys said nope.
you should also try snow sliders fix before getting more involved in the brake bleeding process

This years Hayes are pretty bad for that - the adjuster screws back out easily. I ended up having to loctite mine.

zion zig zag
06-02-2004, 09:23 AM
Originally posted by altagirl
This years Hayes are pretty bad for that - the adjuster screws back out easily. I ended up having to loctite mine.
I think i'll loctite as well. I end up screwing mine back in on everyride.

altagirl
06-02-2004, 09:25 AM
Originally posted by flykdog
I think i'll loctite as well. I end up screwing mine back in on everyride.

Just be very precise to only get it on the threads. Got too much on one side the first time and ended up having to take it all apart and clean it and start over.

Big E
06-02-2004, 09:42 AM
It could be air (thus needing a bleed), but I somehow don't think that's it, at least not entirely. Right now, the lever goes all the way to the handlebar and the pad towards the inside of the bike is still a good 0.5 mm from even touching the rotor!

I think I may just roll by the bike shop tonight and ask them to look at it, maybe they'll do it while I'm hanging around.

I still have a lot of work to go honing my bike mechanic skills.

edit - I dorked around with the adjustment screw on the lever, and it seems like things are just so out of whack that little micro-adjustments aren't going to cut it. I need a macro-adjustment.

phUnk
06-02-2004, 12:29 PM
It's unlikely that he crashed and introduced air into the brake line (thereby needing a bleed).

Big E
06-02-2004, 12:59 PM
Originally posted by phUnk
It's unlikely that he crashed and introduced air into the brake line (thereby needing a bleed).

Well, actually, maybe not. I hadn't really even thought about this, but I noticed on Shimano's maintenance tome that turning the bike upside down could have done it. Air that was in the teeny-tiny reservoir at the top of the system gets inverted, bubbles down to caliper. Could have happened. Hadn't thought about it until I read it, but seems obvious now.

Oarhead
06-02-2004, 02:26 PM
First the mushiness: you need a bleed from the sounds of it. Another possibility is that the brake line has a tear/weakspot and the pressure is deforming the line instead of pushing the pistons. Check the line before you do any of the other stuff.

Now: It is possible that the pads are not centered properly. You may have pulled on a lever when the disk was not between the pistons and one never returned to the original position. This is a pain in the ass. [When travelling with the front wheel out shove a chunk of folded carbooard between the pads so that they don't close up if you accidently hit the lever.]

Pop the reservoir cap on the top - also take a look at the oil level in there while you are at it.

You can use a flathead screwdriver with cardboard covering it - so you don't do any damage - and push the pistons back into place.

Re-check oil level/top it up and cap it up.

Put the pads back on, replace the wheel and look at the alignment.

Give the brakes a squeeze and look at the alignment, if it is still not centered then you will probably need to start shimming it out.

From the sounds of it, the caliper is too close to the frame mounts. Using 0.5 and 0.1mm shims move the caliper so that the disk is centered between the pade. Make sure you give the lever a squeeze everytime you reset the caliper because the centering is changing and will try and find a new equilibrium point.

It should take about 30 minutes max (that is how long it took me to do mine after messing with it forever). Once it is done then it should not need too much attention beyond ensuring bolts staying tight.

freshies
06-02-2004, 03:26 PM
according to my lbs, shimano discs (i have xtr, maybe xt different?) do not need to be bled....mineral oil is used, and they are sealed?

Big E
06-02-2004, 03:39 PM
Originally posted by freshies
according to my lbs, shimano discs (i have xtr, maybe xt different?) do not need to be bled....mineral oil is used, and they are sealed?

Mental note - do not go to freshies lbs.

freshies
06-02-2004, 07:06 PM
Originally posted by Big E
Mental note - do not go to freshies lbs.

no kidding...i was like "what?, really?" i asked the guy again and he was saying something to the effect that they do sometimes need to be bled, but rarely, and he didn't reccomend, yadda yadda" i plan on checking the Shimano link posted above....

Mr. Altagirl
06-02-2004, 08:59 PM
Whoever is telling you that they never need to be bled shouldn't work in a shop. I run XT's with 8" rotors on my DH bike and occasionally need to bleed, adjust, tweak. Once I got them shimmed in correctly, I haven't had to adjust the shims but I bleed fairly often and even change out the fluid (mineral oil) occasionally. DH riding is very hard on the system but it really helps to learn how everything works.

Oarhead gave some great advice. One time, I worked on a set for hours and couldn't get them right. I finally changed the line and that fixed the problem. I later put the old line under pressure and found the smallest leak imaginable. I don't think it would allow fluid out but it introduced air in. Check your lines thoroughly just to be sure, then bleed, then shim if necessary. Just my two cents.

Big E
06-04-2004, 06:00 AM
In case anyone other than me cares, bleeding did the trick. Shop fixed that, realigned my derailleur hanger that was causing the poor shifting. Apparently my repair of the hanger when it was obviously bent - taking it off, laying it on a piece of vinyl tile over top concrete, and beating the bejeebus out of it - was not quite perfect. Amazingly close, though, tech didn't think it was bent till he actually measured it.

phUnk
06-04-2004, 10:20 AM
Originally posted by Big E
In case anyone other than me cares, bleeding did the trick. Live and learn. Glad you're back on the road.

I just ebay-scored two new 180mm rotors to replace my 160mm rotors on my Rocky Mountain Slayer for half the price of retail. Stoked!

Mike_A
11-08-2009, 02:11 AM
For the record, shimano's technical documents are now to be found at:

http://techdocs.shimano.com/techdocs/blevel.jsp