Bike Forums

Bike Forums (http://www.bikeforums.net/forum.php)
-   Bicycle Mechanics (http://www.bikeforums.net/bicycle-mechanics/)
-   -   Chain rubbing the inside of the front derailleur one smallest gearing. (http://www.bikeforums.net/bicycle-mechanics/936890-chain-rubbing-inside-front-derailleur-one-smallest-gearing.html)

WK95 03-05-14 05:01 PM

Chain rubbing the inside of the front derailleur one smallest gearing.
 
I recently replaced my bottom bracket and crankset and while tuning my bike up, I noticed that when the chain is on the lowest possible gear (biggest cog and smallest chainring), the chain rubs the inner part of the front derailleur.

The chain line for the crankset is 45mm and the front derailleur is also for 45 mm. The front derialleur

Both the front derailleur and the crankset are Shimano Soras but the front derailleur is front the last gen. one. However, seeing as the chainline is the same at 45 mm, they should both be compatible.

As for the limit screw, I've loosened it all the way but the problem still persists.

I'm thinking that I might possibly need bottom bracket spacers.

I'll try to measure my chainline later.

cny-bikeman 03-05-14 05:15 PM

Need to check the most basic first - have you loosened the shift cable before adjusting the inner position?

WK95 03-05-14 05:36 PM

The chain is rubbing even though the I've completely loosened the cable and the lower limit screw.

WK95 03-06-14 01:38 PM

Bump

The new crankset that I am using is also the same number of speeds as my old crankset and since the chainline is the same at 45 mm, I'd expect it to work together perfectly without needing any spacers.

cny-bikeman 03-06-14 01:53 PM

IF the outside of the derailleur cage is parallel to the chainwheels and the derailleur is only 2-3 mm above the chainwheel and you changed nothing in the back then the only fix is to add a spacer. You might check from the rear to see if the chainline is good by eye from front to rear.

j814wong 03-06-14 05:23 PM

Quote:

Originally Posted by cny-bikeman (Post 16554660)
IF the outside of the derailleur cage is parallel to the chainwheels and the derailleur is only 2-3 mm above the chainwheel and you changed nothing in the back then the only fix is to add a spacer. You might check from the rear to see if the chainline is good by eye from front to rear.

I have a similar issue. When the lower limit screw is at it's loosest and I shift down to the smallest chainring, the front derailleur hits the frame. This is the same front derailleur that came with my bike but I never noticed that clank sound came from the front derailleur hitting the frame.

cny-bikeman 03-06-14 05:33 PM

Same answer

WK95 03-08-14 11:25 AM

The instructions from Shimano say i need something called a pro-et alignment block. Where can I get that?

WK95 03-08-14 11:57 AM

1 Attachment(s)
Pro-set Alignment block I mean.

Also, I'm a bit confused with the instructions at step 2.

http://bikeforums.net/attachment.php...hmentid=367775

In the seccond picture, why is the hand pulling the cable from the side.

cny-bikeman 03-08-14 12:07 PM

That's "pro-set" and it's just an aid to getting the derailleur in proper position, not a solution to your problem. It will not change anything about the way the derailleur adjusts, but merely shows you where the proper position is. Some pics from the side of the bike directly across from the front derailleur, directly above the derailleur, and looking from behind the rear cogs toward the front derailleur at the level of the chain would help. Better would be in-person assistance from a bike co-op, a friend or a bike shop.

The explanation is wrong - you pull down firmly on the cable AFTER the initial tightening of the bolt, then you loosen it, pull up slack and retighten. The pulling procedure is to help everything seat in properly, and will usually produce some slack in the cable, which is why you have to readjust at the clamp. Some people call the procedure pre-stretching but it does not really stretch the cable.


All times are GMT -6. The time now is 02:22 PM.