Rear derailleur adjustment. The third screw.

veryavgwhtguy · Sep 11, 2008

I know what the barrel cable adjuster, H screw, and L screw do.

How do you adjust the third screw that presses against the derailleur hanger? (obviously your turn it)

But, how do you know when it's adjusted properly?

Is its function to set the distance between the cogs and idler pulleys?

EpicProportions · Sep 11, 2008

In Shimano rear derailleurs (that have it) this is called the B-tension adjustment screw. As you said, it does adjust the distance between the upper pulley and the sprockets.

From Shimano:

1) Mount the chain on the smallest chainring and the largest sprocket, and turn the crank arm to shift gears.

2) Then turn the B-tension adjustment screw to adjust the so that the guide pulley does not interfere with the sprocket but not so close that it touches the chain

3) Next, set the chain to the smallest sprocket and repeat the above to make sure that the pulley does not touch the sprocket.

Turning the screw counter clockwise will bring the pulleys closer to the sprocket, whereas, clockwise movement will bring the pulleys further away from the sprocket.

Shimano recommends that the pulley be approximately 5-6mm from the largest cassette sprocket. This should be rechecked and readjusted if the cassette is changed to one with different tooth counts.

upsidedown1 · Sep 11, 2008

For SRAM X-0, X-9 etc same thing except you should have a 6mm gap between the pulleys and large cog in the back (well at least that is what they say).

IAmtnbikr · Sep 13, 2008

I've found often that you can't get the derailleur sufficiently close to the cassette unless you tweak the mount. On my new NRS build I had terrible shifting issues and finally went ahead and machined the hanger to allow the derailleur to move quite a bit more than the normal adjustment first allowed in order to bring it to the correct 5mm-ish point. Seems that this happens all too often if you actually check the clearance.

keith_mahoney · Sep 15, 2008

IAmtnbikr said:
I've found often that you can't get the derailleur sufficiently close to the cassette unless you tweak the mount. On my new NRS build I had terrible shifting issues and finally went ahead and machined the hanger to allow the derailleur to move quite a bit more than the normal adjustment first allowed in order to bring it to the correct 5mm-ish point. Seems that this happens all too often if you actually check the clearance.

That may be the case for your bike, but on both my Cove Handjob and my Trek 6500 both with different model XT Derailleurs I can get the top pulley resting on the cassette. Actually on the cove that is how it set up out of the box. I have quite a bit of the screw turned in to get clearance.

Spartacus Rex · Sep 15, 2008

Same with moto lite

keith_mahoney said:
That may be the case for your bike, but on both my Cove Handjob and my Trek 6500 both with different model XT Derailleurs I can get the top pulley resting on the cassette. Actually on the cove that is how it set up out of the box. I have quite a bit of the screw turned in to get clearance.

I have the same issue on my wife's MotoLite. Had to turn the B-screw in almost all the way to get 5mm clearance

Rear derailleur adjustment. The third screw.

veryavgwhtguy

EpicProportions

upsidedown1

IAmtnbikr

keith_mahoney

Spartacus Rex

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