So I thought this would be simple enough but there seems to be a large variety to choose from. I have an XT rear derailer from the 90's (8 spd) that has a super squeeky pulley. I would rather replace it and it looks beyond keeping anyway. What am I looking for in a replacement. I am amazed at the options for such a simple thing.
Thanks,
Scott

I just lube them when they squeak..

Replace when teeth have completely disappeared

You want something compatable. Pulley diameter doesn't have to be spot on, but pulley thickness and bearing shaft diameters need to match exactly. Shimano replacements list the compatable models printed on each package.

When installing, make sure they go in the right places. The guide pulley goes on top and the tension pulley on the bottom. They're usually marked, the bearings are different, and so is the lateral play.

There is literally nothing better than the original equipment pulleys. All those aftermarket machined aluminum things suck.

No, the pulley can't be too big, but as long as the hole is big enough that'll do. If it's much thinner or thicker you'd need to shim that pulley or the other pulley with a pair of washers.

It won't matter if the pulley's sitting a mm off-centre of it's bolt in the cage, and you can calmp it centred if you like anyway.

Yeah, but a cartridge bearing craps all over a bush. The best pulleys are the fancy BB plastic OEM ones... haven't seen plastic aftermarket ones aside from cheapies.

I would kinda think that any pully that's too big couldn't actually be installed. 'Doesn't have to be spot on' to most people would nean 'should be close but doesn't have to be an exact match'. Hope that clarifies things and sorry if initially that went over your head.

But the concept of sticking anything through a jockey wheel with no regards to minimum shaft diameter makes me think I'd rather not have you working on my bikes. Ceramic bearings, bearing wear and lateral play don't seem to be anything you'd be concerned about, and I am with the Ultegra, XT and XTR derailleurs I use. Using the recommended replacement parts means you don't have to shim or second guess ANYTHING. And thats what any professional mechanic would do.

I've never seen a jockey wheel that used the bolt's shaft as a bearing surface, hence I've never seen a jockey wheel that requires an exactly matching bolt.

Nothing went over my head; you say the size doesn't have to be spot on, and I say it can be miles off as long as the pulley and chain have clearance (many MTB derailleurs have huge jockey wheels that can be replaced with much smaller ones in a pinch).

Obviously the correct parts are preferable, but questioning the standards of someone rightly saying this area isn't critical is a cheap shot and pretty lame, IMO. I could perform every kludge in my book on your derailleur and you wouldn't know a thing from riding it 5000km.