Mountain Biking - XT disc help needed :)

:confused:

Hello to all,

New to this forum I am. Odd really since I am involved with a few other forums and yet even though I'm a bike knut this will be my first posting on the subject. Oh well there you have it.

Now on to business!
Not so long long ago I took the plunge to disc velocity assasins... (Note to self: shut up they'll think you're a feckin' ejiot)
Sorry, ah hem.
I bought a Shimano XT disc setup and bolted it to my Duke fork. I did it by the book and everthing went according to plan. Now the problem is not that they don't work, they do. To be honest though they work just about as well as the deore V-brake which preceeded it, obviously not the jump in performance I was looking for. Now trust me when I say it all went according to plan. There is no oil on the pad, the bleed was sucessful and it has been given PLENTY of bed-in time etc.

To add insult to injury the rotor rubs annoyingly on the pads after a heavy brake. Now we're not talking the odd brush, we're talking full on grinding. It clears its self off after 2-3 lighter touches of the lever, but still occurs when the frame flexes. Thats another thing the rotor has a slight kink (from birth) and this makes medium braking feel juddery.

I went in for a closer look and the two outside pistons are protruding about 1-2mm more than the inside ones. This is causing the disc to be off centre. I have reset them several times but I end up with the same result. Shims will only make the problem worse as the outer pistons are the problem.

Now the shop of origin has told me that everything is as it should be. They have tried some bizzare stuff to try and sort it, I don't want to go into that, but ultimatly I'm still at square one.

I'm not a happy camper and I was wondering if anybody had an opinion on whether this piston thing is normal, or if infact, if any of the above is normal? Solutions/suggestions welcome.

Sorry if the post is sloppy it is after all 05:59 :eek:

Thanks all,

You should have bought Magura/Hayes discs :)

Nah dont listen to him....XT beat maggies all the way. Just wait. I waited a month for my XT to bed in. Now they stop like a brick wall.

The only thing I can say is that a friend (also a mechanic at another shop) swears by his XT discs, however, he hated the stock pads. He switched his out to some EBC Red Compounds. Here's a link:http://www.cambriabike.com/brakes/mtb_disc_brake_pads.htm

Scroll down a ways!

They were the FA 310's.

He said the original pads were awful! Same problem, no power. He switched pads and said it was like night and day!

L8R

XT beat Magura? You have got to be kidding me. Seriously.

Hope Discs for life :)

Yeah, good point :)

Well I've had them for about a month now. I wouldn't mind waiting longer for them to bed-in if I could just be convinced that the unit wasn't faulty. You see it's the protrusion of the pistons that really bothers me, and the fact that this causes the disc to be 'to close for comfort' to the pads.

You see I don't want to be left in the situation where I go back to the shop after 3 months to be told, '...yes well we can't replace them now because they are too old', that would just make me mad.

Perhaps Math, or anyone else, could have a look and tell me if your pistons protrude unevenly, even to a slight degree? I want to be able to go to the shop and say with certainty that what ever the case this particular thing shouldn't be happening.

If I could rule all this out then I might be inclined to pump hard currency into trying a different compound.


Thanks again,

In crap conditions thats for UK weather ...the stock pads are awesome ...they bed in fast and brake like hell. Of course they need mud and water treatment first. If you are in a dry dusty enviroment then go for EBC red almost immediately....and also switch to goodridge brake lines ...huge performance gap in comparison with any other brake line. Oh yeah XT beat maguras anytime....anyplace ...given i am behind the bars. (handlebars and not prison bars :D).

And how do you make XT work better than a lovely set of Louise's :)

Look did you have any bad luck with XTs? If yes plz tell me.

I just asked a simple question :)

Avid mechies all the way. Superior adjustability with the levers and no bleeding. Stop on a dime. Installed and riding in 15 minutes.

Hey Converse,

Did you buy them on-line or from your LBS?

If from you LBS, and they can't get them to work correctly what is their solution? You said they've tried some crazy techniques to no avail. What about a refund or replacement? Our shop always stood behind the products we sold/installed. If nothing else, they could call Shimano Tech Line (not avail to general public). Shimano should know what to do, or get you a replacement.

L8R

From the LBS. They acknowledged that they rub but said it was within normal parameters. They tried to reduce the rubbing with methods that made me cringe. The said the piston protrusion thing was also normal. I myself think the misalignment is too severe but what can I say to them unless I have some 2nd opinions?

Keep it coming!
Cheers,

Originally posted by Buzzbomb
Avid mechies all the way. Superior adjustability with the levers and no bleeding. Stop on a dime. Installed and riding in 15 minutes.

Hey...thats what it was like to install my hayes hydros...amazing.

Can you take a picture of the situation?

The only other thing that could cause some heartburn is there may be some paint on your disc tab. From your description, it's not the case, but remove the caliper and take a razor blade and try to scrape the inside of the tab clean from paint or ???. Then lightly (I mean lightly) sand the area smooth with emory cloth or 440 wet dry.

There is a device that very few shops have that will face and align the disc tabs. Usually you can get pretty close by sight.

This can be the only other thing causing a problem.

As far as the piston protrusion, that's pretty normal. However, they should retract without have to re-squeeze the lever. That's odd.

I'll check with my buddy who runs XT's and ask him if he's had any other problems similar to yours. Probably won't get to speak to him untill the weekend, so be patient.

L8R

Hi psyklnut,

Unfortunately no pictures available, as I say in my 'introduction' some little brat now has my cam!

The bike shop did suggest I pry the paint from the tab (on the fork, you meant, I take it ). I was a bit sceptical about this solution and I wanted to rule out any mechanical fault first. I'm about to do 7 x 12hr night shifts in work so I won't be able to do anything till then anyhow.

Let me know what your mate says, I'll stay tuned to this channel.

Thanks very much for your efforts.

Xt are also installed in 15mins. The pistons should retract all the way. If not...then try to lubricate the pistons with some mineral oil (pads removed of course) . Also check for correct bleed and air bubbles. Pay attention to the correct state of the retracting springs between the pads. Oh and yes XT ripe the guts of magura.

No one I know who runs Avids had any probs installing them - ever. This post makes these brakes seem like a real PITA. I like my bike bombproof. I'm just glad there's enough stuff out there to choose from so that we're all happy with what we've got...

Buzz,

To be honest there have been problems with all brakes. In the mech section someone had issue with avids. People have problems with hayes. No braking system is clean and perfect. Its depends on luck of quality and the riders own mech skills. Personally if I had a choice I would go Hope, Hayes and Shimano XT in that order for brakes. Shimano's brakes are becomming really popular out here for being exceptional in really crappy conditions (a big selling point in a rain forest)

My riding in the summer is mostly dry and dusty, winter riding is a different story, tends to be real cold. I try to avoid the really sloppy stuff... And yeah, I agree, any mechanical thing, car, boat, bike, is gonna have some problems. It's just hard not to cheer for the team your running ;^)

Hi people,

Just having a close look at matters again. I have noticed that even if I gain an extra mil or 2 clearance for the pads by removing the paint from the tab this will not solve the problem. In fact this will leave very little space between the caliper and the disc. So little infact that it seems the disc may start grinding on it.

Any opionions on this?

Thanks

1 mm spacers. Very thin, available at "good" hardware stores or most LBS's.

Get some and do this. Loosen the bolts holding the caliper to the frame. While still on the rotor, squeeze the lever and put some velcro or a rubber band around it to keep it squeezed (squozen sp?). This will center the caliper on the rotor. Put enough spacers in between to fill the space. Tighten the bolts back up and release the lever.

Does that help?

If not, I'm at a loss.

L8R

Unfortunatly not psyklnut, you see shims/spacers would make the problem worse. It is the outer pistons/pad that is the problem so adding these would actually bring the caliper closer to the rotor.

When you said about removing the paint, did you mean from the fork tab?

Thanks

I don't have alot of experience with disc brakes, but I have installed XT's a few times. Every time I had to take a file or something and file away the paint on the dics tabs, on the fork, and on the frame. If I didn't, it was near impossible to get the pistons lined up right.

Just get to an LBS that has a facing tool and have them do the job. That way your problems will end plus you will make a good contact with them. If you are handy then try to face the adaptors yourself.