Splatter Paint
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All, those of you running late 8 speed XT & XTR and certainly 9 speed XT & XTR systems should find this useful. After a particularly bad ride, marred by continual chainsuck I stripped my bike down to diagnose the problem - after ordering two new XT chainrings and an XTR chain 
it turns out that the chainsuck was caused by failure of the sealed bearing jockey wheel on the rear mech. The bearing had seized, causing the chain to go slack on the lower chain run and hence get dragged up into the chainstay.
The lower jockey wheel on XT & XTR is a sealed roller bearing, pressed into a plastic cog. An XT one is £17.99 to replace and XTR one £18.99!! To save yourself some money and some rather unsightly chainstay damage you can service the 'sealed' bearing, prolonging the life.
Simply undo the lower jockey bolt on the rear mech, you will then be able to remove the two aluminium washers and steel shim from the jockey. I've not actually had an 8 speed unit apart but I assume they are the same as the 9. The XT jockey has a steel seal which is rubber lipped, stopping the ingress of dirt, the XTR one is all rubber but the principal is the same. Using a very small screw driver prise the seal out of the bearing on both sides, this will expose the rollers. Mine were caked in black mud and grease mix
Then flush through with solvent or WD40 and dry thouroughly. Then pack with a THIN grease, Castrol LM bearing grease is ideal. Now fit one of the seals, this will push the grease through the ball race. Now add a bit more grease to the other side and refit the seal. Wipe away the excess grease, refit the two alloy washers and steel shim and refit to the bike.
If you removed the jockey and found the innards were all white, then you've removed the guide or 'G' pulley, this should be mounted at the top of the mech, not the bottom. Give it a clean and re-fit. Since it is ceramic I don't think it requires greasing.
Below is an exploded diagram of an M750 mech but the earlier and later models are much the same.
http://techdocs.shimano.com/media/techd ... 611911.pdf
SP
it turns out that the chainsuck was caused by failure of the sealed bearing jockey wheel on the rear mech. The bearing had seized, causing the chain to go slack on the lower chain run and hence get dragged up into the chainstay. The lower jockey wheel on XT & XTR is a sealed roller bearing, pressed into a plastic cog. An XT one is £17.99 to replace and XTR one £18.99!! To save yourself some money and some rather unsightly chainstay damage you can service the 'sealed' bearing, prolonging the life.
Simply undo the lower jockey bolt on the rear mech, you will then be able to remove the two aluminium washers and steel shim from the jockey. I've not actually had an 8 speed unit apart but I assume they are the same as the 9. The XT jockey has a steel seal which is rubber lipped, stopping the ingress of dirt, the XTR one is all rubber but the principal is the same. Using a very small screw driver prise the seal out of the bearing on both sides, this will expose the rollers. Mine were caked in black mud and grease mix
Then flush through with solvent or WD40 and dry thouroughly. Then pack with a THIN grease, Castrol LM bearing grease is ideal. Now fit one of the seals, this will push the grease through the ball race. Now add a bit more grease to the other side and refit the seal. Wipe away the excess grease, refit the two alloy washers and steel shim and refit to the bike. If you removed the jockey and found the innards were all white, then you've removed the guide or 'G' pulley, this should be mounted at the top of the mech, not the bottom. Give it a clean and re-fit. Since it is ceramic I don't think it requires greasing.
Below is an exploded diagram of an M750 mech but the earlier and later models are much the same.
http://techdocs.shimano.com/media/techd ... 611911.pdf
SP
