Shimano 7400 Rear Mech question

[acorn_user]

Hey all,

so I wore out the lower pulley wheel of my derailleur with a chain that also blitzed my cassette. Oops. I have been told that I cannot use the upper pulley wheel from a spare 7400 rear mech to replace the worn lower pulley wheel. Could I pull a lower pulley wheel from a spare Shimano Sora or Campagnolo Centaur rear derailleur to keep the thing going, or do I need a specific Shimano part for the repair?

Thanks!

[oliver1850]

Do you have a 7400, not a 7401? I found that the pulley widths are different between 6400 and 6401, so if you swap, you need to swap both pulleys.

I would use any 10 tooth lower pulley that's the same cage to cage width as your top one. I can check some used RDs for something that will work, but I only have a 7401 for reference, not a 7400. I'm guessing the 6400 and 7400 are the same.

[PacNW2Ford]

7 or 8 speed? If seven, or it doesn't matter, I have a busted 7-speed 105 RD we could strip for parts.

[oldpotatoe]

Hey all,

so I wore out the lower pulley wheel of my derailleur with a chain that also blitzed my cassette. Oops. I have been told that I cannot use the upper pulley wheel from a spare 7400 rear mech to replace the worn lower pulley wheel. Could I pull a lower pulley wheel from a spare Shimano Sora or Campagnolo Centaur rear derailleur to keep the thing going, or do I need a specific Shimano part for the repair?

Thanks!

All ya gotta match is the width and the bolt hole diameter. Just about any 10t pulley from any other RD, the lower pulley, will work. If it's too narrow, add some wee washers to either side.

[acorn_user]

Ok, it's a 7400 rear derailleur. The pulley on it at the moment was pulled from a 7402. I guess I'll see if I can plunder one from a broken mech or from my spare Sora/Mirage bits.

Thanks!

[acorn_user]

The Sora has an 11t jockey wheel, whereas the original part is 10t. Is that a problem?

[Brian Smith]

If the indexing performance is important to you with this 7400 RD, you mainly need the proper upper pulley and the proper width lower pulley. You can use your spare upper pulley as a lower, though I understand multiple reasons why someone might tell you that you can't. My hunch is that simply economy is the main factor in this pulley replacement, and if you're choosing among used free(-ish) pulleys, you should choose, in my opinion, the spare upper pulley (though that one would be worth more to a restoration specialist than the attendant replacement lower pulley, perhaps they'd swap with you,) or another 10t pulley with appropriate width spacer washers added on each side of the new pulley to keep it aligned with the center of the G-pulley (upper), or else the benefit of the upper pulley is at least partially lost anyway. In shops in the past, I've sold those replacement upper pulleys for over $50, these days an entire 7400 derailer in used condition is probably not worth half that. If you're not using 6-speed cassettes or 6-speed Dura-Ace freewheels, I'd suggest buying a replacement used derailer of newer vintage instead of trying to patch up the 7400 with used pulleys. The indexing performance would be better, no matter what the model name label on the derailer says.

If the indexing performance is of no consequence, and you're using friction shifting, I'd suggest replacing the pulleys with a matched pair of 10t pulleys from any derailer in any condition over mixing and matching pulleys of any types.

hth...

[acorn_user]

Brian, thank you for taking the time to respond. I went and bought a set of Shimano pulleys and am going to install those. Thank you also for suggesting a replacement. As I understand it, I cannot use my Dura Ace 8 speed STI levers with any other kind of derailleur. Is that so?

[Grant McLean]

As I understand it, I cannot use my Dura Ace 8 speed STI levers with any other kind of derailleur. Is that so?

No, that's not so.

You can use a 9 speed rear derailleur with an 8 speed STI lever.
I had a 7700 rear der on my serotta with 7402 sti for years,
worked perfectly fine. The float in the upper pulley allows
for some wiggle room too.

-g

[oliver1850]

I agree with what Grant said. 7700 bar end shifters say right on them that they can be used with 7400 RDs, so it should work the other way as well.

When Shimano went to 9 speed, they evidently kept the geometry of the 8 speed DA RD. So a 7700 or other 9 speed should work with 7400 shifters. I don't think you can do that with 105 or 600 7/8 speed shifters, because those RDs had a different geo than DA.