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Front Derailleur is hitting middle chainring!
#1
Hi everyone!

Basically I've been fixing up my MTB with new parts. I've added a Shimano FD-M591 and RD-M591 to the front and back Derailleurs, respectively. I've also changed the chainset to a Shimano Tourney M151 (48/38/28T).

My issue is that the inner side of the front Derailleur is way larger than that of the outer side, so if I mount it as per Alex's tutorial on the main site - the inner cage smashes into the middle chainring when trying to change up!

If I mount it higher, the chain is no longer central to the grooves of the cage and rubs like hell in virtually all gears.

Am I looking at replacing the crankset?
Here's a couple of images of the problem...

This one shows the inner side of the cage, it's just clearing the middle chainring....

[attachment=1518]


However if you look at this pic, note how high I've had to mount it to get it to do that....

[attachment=1519]
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#2
This is the installation instructions for your FD;
http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_6S80A/SI-6S80A-001-ENG_v1_m56577569830667673.PDF
and the chainset it is recommended for;
http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/FC/EV-FC-M590-2926B_v1_m56577569830696742.pdf
you will see the max middle chainring is 36t, you are using it with a 38t?
It always advisable with Shimano to check compatibility before buying.
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#3
Good point, I wished I had now. I really didn't think this would be a problem. We live and learn I guess!

Now, to buy a new crankset Big Grin
  Reply
#4
I expect it will be significantly cheaper to change the FD than the crankset, unless you have problems with shifters etc. But I would get it checked out at your nearest bike shop before spending any money the increase in radius between 36/38T is going to be <5mm this shouldn't be enough to cause the symptoms you are describing
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#5
Yup, so I've been finding! The matching Deore crankset to my FD is over £50 whereas a compatible FD can be had for 10.
  Reply
#6
Are you sure that you have the FD installed and cabled correctly - the number of teeth on a chainring isn't that important it is the difference between the number of teeth between the chainrings the differences between these are very small and certainly shouldn't cause the rear of the cage to hit the 2nd ring when on 48T.
As a stop gap I put a XT FD-771 on my hybrid with a 50-39-30T road triple fully 6T above the FD spec and it shifts so well that I have never bothered to change it, I do about 300KM + per week commuting to work and back.
I would definitely advise getting it checked out before spending any more money. It may even be a manufacturing fault with the FD or a bent chainring.

regards

Jon
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