REVIEWS DEALS BIKESHOPS TRAILS

Shimano pulley compatibility

5056 Views 9 Replies 6 Participants Last post by askjasonbowen, 7 mo ago

Octopuss

Discussion Starter · Jul 24, 2021

I have M7100 derailleur on both bikes. I found out the XT, M8100 uses bearings instead of bushings in the pulleys, supposedly affecting shifting in positive way, so I bought a pair, but they don't seem to fit - when I screw them into the cage, they refuse to turn.
I thought the derailleurs are physically identical, only being different in materials used. The cage and the pulleys definitely do look identical, so what's wrong?

Save

1 - 10 of 10 Posts

wschruba

· #2 · Jul 24, 2021

Check that the bearing shields (thin aluminum plates with minor profiling) are still on. You shouldn't see a cartridge exposed with the Shimano pulleys.

Save

DtEW

· #3 · Aug 1, 2021 (Edited)

Octopuss said:
I have M7100 derailleur on both bikes. I found out the XT, M8100 uses bearings instead of bushings in the pulleys, supposedly affecting shifting in positive way, so I bought a pair, but they don't seem to fit - when I screw them into the cage, they refuse to turn.
I thought the derailleurs are physically identical, only being different in materials used. The cage and the pulleys definitely do look identical, so what's wrong?

You made an assembly error somewhere. Or bought the wrong parts.

I bookmarked this thread because I had the same upgrade scheduled and with parts-in-hand, but just hadn't gotten around to it yet. You had me worried that Shimano had made some unprecedented change in their approach.

So now I'll confirm that the XT M8100 bearing-equipped pulleys are straight drop-in replacements for SLX M7100 bushing-equipped pulleys. There is no issue. Just use the existing SLX cage plate and the existing SLX bolts.

Be sure that each XT pulley has both of its supplied, specific aluminum spacer plates on each side. It should be obvious that the SLX bushing shields should not be used. Each pully is also direction specific. And be sure your chain is routed correctly through the cage.

And here's some photos for general documentation:

SLX RD-M7100 pulleys. Top on top, bottom on bottom. Top pulley bushings uses metal on both surfaces; the inner bushing is darker and might be oil-impregnated, the outer bushing looks chromed with channels. Bottom pulley only uses metal for the inner bushing, which looked chromed. There's not a shred of sealing in sight, and only the stamped-steel shields... so I'm surprised it all works as good as it does. Nothing felt obviously lubricated. I'm thinking it was designed to run dry, or assembled with light lubrication: there was no hint of grease.

XT RD-M8100 pulleys. Top on left, bottom on right. Straightforward sealed-ball-bearing pulleys with aluminum spacer/shields. As decent as the SLX pulleys were at 400 miles of use, I'm sure the XT pulleys will retain its resistance to developing runout for much longer.

See less See more

Save

Reactions: 2

Octopuss

Discussion Starter · #4 · Aug 3, 2021

I eventually found out what the problem was - the XT pulleys were a little narrowed, or rather, the caps on the SLX pulleys protrude to the sides a little. There was a little cut on the cage with a piece of metal going inwards which, combined with smaller space around the pulleys, caused them to drag. I filed it away and now it's all good.

Save

Reactions: 1

DtEW

· #5 · Aug 3, 2021

Octopuss said:
I eventually found out what the problem was - the XT pulleys were a little narrowed, or rather, the caps on the SLX pulleys protrude to the sides a little. There was a little cut on the cage with a piece of metal going inwards which, combined with smaller space around the pulleys, caused them to drag. I filed it away and now it's all good.

You are correct. I just checked with a pair of calipers on the remaining XT set vs. the take-off SLX set... and the XT pulley w/spacers assembly is ~0.1mm narrower. But otherwise without any damage/protrusions from the derailleur cage, the fit is just fine.

Save

Twan8100

· #6 · Aug 3, 2021

DtEW said:
You made an assembly error somewhere. Or bought the wrong parts.

I bookmarked this thread because I had the same upgrade scheduled and with parts-in-hand, but just hadn't gotten around to it yet. You had me worried that Shimano had made some unprecedented change in their approach.

So now I'll confirm that the XT M8100 bearing-equipped pulleys are straight drop-in replacements for SLX M7100 bushing-equipped pulleys. There is no issue. Just use the existing SLX cage plate and the existing SLX bolts.

Be sure that each XT pulley has both of its supplied, specific aluminum spacer plates on each side. It should be obvious that the SLX bushing shields should not be used. Each pully is also direction specific. And be sure your chain is routed correctly through the cage.

And here's some photos for general documentation:

View attachment 1941259
SLX RD-M7100 pulleys. Top on top, bottom on bottom. Top pulley bushings uses metal on both surfaces; the inner bushing is darker and might be oil-impregnated, the outer bushing looks chromed with channels. Bottom pulley only uses metal for the inner bushing, which looked chromed. There's not a shred of sealing in sight, and only the stamped-steel shields... so I'm surprised it all works as good as it does. Nothing felt obviously lubricated. I'm thinking it was designed to run dry, or assembled with light lubrication: there was no hint of grease.

View attachment 1941260
XT RD-M8100 pulleys. Top on left, bottom on right. Straightforward sealed-ball-bearing pulleys with aluminum spacer/shields. As decent as the SLX pulleys were at 400 miles of use, I'm sure the XT pulleys will retain its resistance to developing runout for much longer.

Can you provide link of product ? Would love to upgrade mind

Sent from my iPhone using Tapatalk Pro

Save

DtEW

· #7 · Aug 3, 2021 (Edited)

Twan8100 said:
Can you provide link of product ? Would love to upgrade mind

Here's some:

Bicycle Rear Derailleurs for sale | eBay

Get the best deals on Bicycle Rear Derailleurs when you shop the largest online selection at eBay.com. Free shipping on many items | Browse your favorite brands | affordable prices.

rover.ebay.com

They normally go for ~$20/set. I honestly don't think they're going to make an instantly noticeable difference unless yours is worn-out and sloppy. Whether they're worth twice as much nowadays and requiring a month of international transit is up to you.

Save

Reactions: 1

MTB Engineer

· #8 · Aug 4, 2021

I had 5000km on my XTR pulleys before I had to replace them due to a broken tooth. The other teeth were still fine with just barely measurable wear, but the bearings were getting sloppy.

Save

DtEW

· #9 · Aug 24, 2021

Twan8100 said:
Can you provide link of product ? Would love to upgrade mind

Now back in stock at regular price at Universal Cycles, mfg item # Y3FW98010.

Save

askjasonbowen

· #10 · 7 mo ago

Hi all,
Shimano 12s uses a 13t pulley set. Can I purchase an aftermarket set of pulleys with different size teeth and will work?

Save

1 - 10 of 10 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month