questions and advice on re-packing hub bearings (XT HB M-756s)
 

I'm thinking about doing a DIY bearing re-pack on my front and rear Deore XT hubs. They are running smoothly, but it's 1) been "enough" miles (yeah, i probably should have done it earlier), and 2) i figure it's time to learn how, and from what i can tell it's not too difficult (i have time, patience, and am willing to supplement my tools if need be).

Can anyone tell me:
1) what size and how many bearings i'll need for the hubs (they're XT HB-M756 front and rear). I briefly Googled, but couldn't find anything specific enough to felt like i knew for certain (fronts is maybe 3/16ths, 20 total; rear is maybe 1/4s, 18 total?).

2)I have figured out that grade 25s are what i want quality-wise; any recommendations for a loose BB supplier, or for preferred BB grease? (For the latter, i've heard rec's for marine BB grease, and white lithium, among others.)

3) is a tool like the "freehub buddy" necessary for a good re-packing, or can it be done reliably to spec without one?

I'm primarily concerned about the front hub, since the rear hub is mostly out of commission; but i'd figure i'd do both if i was already going to do one. I looked up the instructions at Park Tools, and figure i'll just follow those (theirs seems mostly dedicated to the rear, so i presume the front it much less complicated).

Any other tips or points?
Thanks all!

Typical size:

front hub........................3/16"......................10 per side
rear hub.........................1/4"........................9 per side

I got this from: http://www.bikeforums.net/showthread.php?t=158132

I use Park Tool Polylube in my hubs.

The 9/side of 1/4" bearings are pretty universal for Shimano rear hubs of all models.
The 3/16" bearings are also universal for Shimano front hubs but some take 10/side and others take 11/side.

You can get Grade 25 bearings at any industrial supply shop or from Bike Tools Etc. ( www.biketoolsetc.com ). Get a bag of 100 of each size and you are good for a few years.

I've never used a Freehub Buddy and see little need for them. Remove the freehub body from the hub shell with a 10 mm Allen key after you take out the axle and bearings. At the back of the freehub body there is a rubber seal. Carefully pull it out and drip a lot of Tri-Flow or similar light oil onto the exposed bearings, spin the body to distribute the oil and replace the seal. Reassemble the hub with new bearing balls and fresh grease. I've got a set of hubs with 55,000 miles on them and the freehub has been lubed this way for it's entire life.

I happen to like Phil Grease but there are many suitable greases. Just don't use anything too heavy.

Also see Shimmano's web site and find the link to their technical documents for a view of your hubs and Park Tool's web site for a tutorial on hub overhauls.

Perhaps I'm misreading it, but from the way this is worded, it sounds like you're asking if you need a Freehub Buddy to repack the axle bearings. If so, you definitely don't need one for that. That tool is only applicable for lubing the freehub bearings on a Shimano rear hub, which is a separate job from repacking the axle bearings.

The balls should not need replacing for a sizable amount of time, like years. In my experience, in fact I have never replaced the balls on a well maintained hub. That means regreased at 500 miles or less in trail use). Make sure to use a good automotive disc brake grade grease. Bike shop grease may work but it costs an arm and leg compared to automotive. If you have disc brakes, it is mandatory as the disc rotors can get hot enough to melt the normal mundane grease types.

I'd disagree with that. The cost of new ball bearings is so minimal, I wouldn't bother trying to re-use them. You have to take the ball bearings out anyways to remove the old grease. Supposedly the bearings become oval shaped over time, so you'll have to re-adjust the hub after the old bearings settle into the orientation they had before you take them out. New bearings will assuredly be spherical shaped. :)

That's true. They are cheap, even for good ones like Grade 25.

That's not true. The "tech guru" from Bicycling Magazine use to publish that myth about once a year until an engineer from one of the big bearing manufacturers (Timkin, IIRC) finally got tired of it and wrote to say it wasn't true. A couple of times I've reused bearing balls with several thousand miles on them and getting a good, stable bearing adjustment was just as easy as with new balls.

Since the speeds the balls are run at are pretty low, the failure of them is almost always from fatigue or poor lubrication (usually caused by water and dirt in the grease), and not frictional wear. fatigue failures will show up as chips and pocks missing from the balls, and lubrication failures as wear. Basically, if you clean the balls in solvent, and they look shiny as new, they're almost certain to be okay, because the hardened shiny part is the first thing that wears away when they're worn. That said, I don't reuse them unless there's a reason (suitable replacements not handy, and I want to get mud out of a hub, for instance. Or they're the metric balls in a set of pedals I have...) to do so, since they're cheap.

PW, I did a quick re-pack a couple of weeks ago. I removed the cassette on my MTB because I had the Park cassette tool and chain whip tool to remove the lock ring. However when I did the road bike a couple of days later, I didn't remove the cassette and for that matter I only removed the nut, spacers and cone from one side of the axle which kept everything centered.

You will need a magnet tool to get at the bearings and you'll have take your time putting them back in; its a little bit of a reach to get them back in place but certainly a lot quicker unless you are changing cassettes. The grease (I use marine water proof grease) holds them in place nicely you can pick it up at any autoparts store.

Cone wrenches are a must unless you have some really thin gear wrenches that might fit in between the cone flats and the lock nut.

For as little as the balls cost it wouldn't hurt the pocket to change them and re-pack every winter when just touching the bike feels good lol. I paid several cents each for new bearings, literally had less then a buck or two in both front and back.

Don't use a magnet on balls you want to reuse, nor to install new bearings. There's a real risk of magnetizing the balls, which will cause stuff to stick to them.

As far as the replace or reuse debate, I have restored a great many units where they should have been replaced on the basis of what the machine looked like but they were in fact quite serviceable. Only one hub I have had ever "Neeed" them replaced and it was interestingly enough 6 months old! My 40 year old Schwinn road bike still has glass smooth originals on high miles.

In Bicycling Magazine's manual it states that any ovalizing in the bearing balls is adjusted out in the first few cycles around as you tighten the preload and then re check it. Thus far it has proven true for me. As one has stated, bikes are not high-load applications. Water and sand are the enemies.

hum...never thought of that, good info. I do only use it to remove the old ones but I roll the new ones in with my fingers. I watched the "bicycletutor guy" use a magnet to remove all of the balls at the same time and thought that was sweet.

Speaking of bicycle tutor...PW take a look at some of his tutoring videos. Below is a bearing overhaul. This site give you a lot of visual instruction, I like to see it done a couple of times. The bicycle tutor site, the Park Tool site and the guys on this forum are about all you ever need. Oh... I forgot Sheldon Browns site - an amazing amount of valuable information there too, I use them all.

http://bicycletutor.com/overhaul-wheel-bearings/

Thanks HillRider, as well as everyone else! Tech docs from Shimano are exactly what i was looking for; i just never realized Shimano would openly publish these.

And yes, Shimano convention holds:
FH: Steel Ball (3/16") 20 pcs
RH: Steel Ball (1/4") 18 pcs

Good times ahead, not to mention many miles.

I stand corrected. That makes sense actually that surface pitting on the bearings would occur first.