Dragging Pulley

[rcrampton]

I've got a 9 speed Deore LX derailleur, 3000 miles on it. I removed the screws that go through the pulleys to clean them out. When I put it back together the lower pulley spins freely, the upper one does not. There isn't enough drag for me to care about other than whether it could be a potential failure on an upcoming tour in the boonies.

I swapped the pins that go through the pulleys and it didn't matter. I noticed that there was loc-tite on the threads on that screw so maybe I'm supposed to tighten it down without causing drag and letting the loc-tite hold it in place?

Thanks for your advice.
Ray

 

[alienator]

If those screws are tightened too much, the pulley will certainly have increased drag. It's also possible that it's just time to replace the pulleys. Your LBS could very well have them in stock.

 

[CAMPYBOB]

Every derailleur I worked on...it was impossible to over-tighten the pulley screws to cause binding. The bushing or bearing sleeve prevented any possibility of binding.

Are you certain you reassembled the parts correctly? Are the cage plates deformed? Bushing dust plates bent?

Have you tried assembly minus the dust plates and checked for drag?

If I pulled up the correct manual on the Shimano website...

[SIZE= 14px]Guide pulley / Tension pulley[/SIZE]
[SIZE= 14px]Tightening torque :[/SIZE]
[SIZE= 14px]2.5 - 5.0 N·m {22 - 44 in. lbs.}[/SIZE]

[SIZE= 14px]That's a pretty decent amount of installation torque for a 3 MM socket head screw.[/SIZE]

 

[rcrampton]

Originally Posted by CAMPYBOB .

Every derailleur I worked on...it was impossible to over-tighten the pulley screws to cause binding. The bushing or bearing sleeve prevented any possibility of binding.

Exactly, there's a bushing that makes sure there is clearance for the pulley to spin freely (now I know after measuring things).

So, I got my micrometers out to figure out what's going on here and found some surprises. Note that I took apart two different Deore LX rear derailleurs and verified this on both:





First, the two pulleys are actually constructed differently. The bottom pulley has an integrated bushing plus a bushing that slides in and out. The upper pulley only has the bushing that slides in and out. The two removable bushings are identical at 0.180" length.

The lower pulley is 0.150" wide, the upper pulley is 0.170" wide. Therefore the upper pulley only has 0.010" of clearance while the lower has 0.030" clearance. When I re-cleaned and assembled the upper pulley is spins pretty much freely now though a little grit can cause some slight resistance. I thought I'd cleaned the heck out of it all but I obviously missed a little something.

Now I'll quit typing and get riding. Thanks y'all!

 

[daveryanwyoming]

Originally Posted by rcrampton .
...The lower pulley is 0.150" wide, the upper pulley is 0.170" wide. Therefore the upper pulley only has 0.010" of clearance while the lower has 0.030" clearance. ...

IIRC, that has to do with chainline tolerance. IOW, the upper or jockey pulley should always run in a very straight line to the cog engaged but the lower pulley has to deal with the chainline angle with the chain running all the way up to whichever chainring is in use. So IOW, the upper pulley sees the chain at a relatively straight angle but the lower pulley has to be able to deal with chainline angle issues so they design a bit of extra lateral float and or clearance for that lower pulley.

-Dave

 

[CAMPYBOB]

"The lower pulley is 0.150" wide, the upper pulley is 0.170" wide."

Are you sure you haven't swapped that?

Usually it is the upper pulley (the jockey pulley) that has some 'float' designed into it to allow for self-centering after shifting. The lower (tension) pulley? I've never heard of a lower pulley that floated. Learn something new every day.

Per Competitive Cyclist:

"One design issue to overcome is the upper “floating” pulley. Most derailleurs that are designed work with indexed shifters come with an upper pulley that has a small amount of sideways pay to account for less than perfect shifting, cable stretch, swapping out wheels, cassettes, etc."

 

[dhk2]

I've never had an MTB rear derailleur, but on my Shimano road derailleur, the floating pulley is definitely on the top. It's a 7700 series, and I'm sure the pulleys haven't been messed with as I've owned it since new (late '03), and I don't believe in taking things apart for cleaning.