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Discussion Starter · #1 · (Edited)
Hi Folks,

I recently picked-up a new to me 2013 RockHopper with very few miles. From the very get-go the bike has been plagued with chain suck issues. All manner of research and fixes have not addressed the problem, and I am tired of fiddling with this thing and just want to go out and ride the bike. Since I am at my wits end, I decided to replace the craptacular Suntour crank and Acera front derailleur with Deore componentry.

As a happy coincidence, I found a seller on a local CraigsList that offered me a Deore XT FC-M770 for an unbeatable price. I also ordered the Shimano FD-M590 to complement the new crank.

Questions:
- Is the combination of XT FC-M770 and FD-M590 optimum? I read that the FD-M590 is a 9 speed FD, and I concerned that this could be an issue.
- Should I order a 10 speed FD instead, perhaps the FD-M770 to match the 10 speed crank? However, if I go this route, don't I have to replace the front shifter as well?
- Do I need to get a new 10 speed chain to replace the 9 speed I have now? Will I have excessive chain rub if I re-use my existing chain?

Thanks in advance!
 

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R.I.P. DogFriend
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Alex, I have reservations about recommending that a new front derailleur will solve your issues. A new one may work fine, but I would first make sure the one you have is mounted and adjusted correctly. Front derailleurs are one of the most finicky parts on a bike to get working properly. They need to be the right height, and they need to be rotated to the right position, they need to have the proper cable tension, and they need to have the limit stops set correctly. And, there is little room for error(s) when setting them up.

A 9 speed chain is a different width than a 10 speed chain, but your 9 speed chain will work fine with the 10 speed crankset.

To recap:

1) I don't think you need to get a new front derailleur to get your bike shifting correctly.

2) I also have my doubts that you actually NEED a new crankset to get your bike shifting correctly.

3) However, the XT FC-M770 crankset will work fine with the drivetrain on your bike.

4) You don't need to replace your chain unless it is worn, and when you do, replace it with another 9 speed chain.
 

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Some more info:
10sp chain has thinner side plates than 9sp. You can run a 10sp chain on 9sp cassettes. The interior dimension and the gears that contact the chain are the same width for 9 and 10sp drives.
Check your existing chain carefully for stretch and kinking or tightness. I would replace it with a KMC 10sp or Shimano HG94/5 chain. Ribble currently has deals on Shimano.
 

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Discussion Starter · #4 ·
Jeffj,

I adjusted my front derailleur per Shimano spec and numerous YouTube videos. I believe I had it configured well based on how crisp my shifts were, when I did not get chain suck, and the small amount of chain rub that I got when cross-chaining.

The only chain-rub that was present, was in the smallest and largest gears on the rear cassette when on the middle cog of the crankset, and in the most extreme cross chaining instances when in the granny and largest crank cogs.
 

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Discussion Starter · #5 ·
I will be running out to get an Octalink ParkTool socket and the wrench required to tighten down external BBs this afternoon, and installing the new XT crank. Also, the new FD-M590 should be delivered this evening, so I'll pop that on. I'll hold-off on getting a new chain for now, until I have the replacement parts installed, and have a chance to try them out.
 

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eb1888 is correct in that you can run a 10 speed chain on a 9 speed system. I know riders that do it and it seems to work for them. That said, I haven't tried it myself to see if it works great or is just passable. If your 9 speed chain isn't worn, I would run it until it is worn.

You will also need a crank arm puller for splined bottom brackets in addition to the socket for removing the bottom bracket itself. Since it will be a one shot deal, you might think about seeing if your shop can do it for less than the cost of the tools. Honestly, it shouldn't take more than ten minutes to remove the crank arms and the bottom bracket (with time built in to use the restroom quickly if needed).

When you say you get chain-suck, are you saying that the chain gets sucked up into the chainstay as it tries to come off the bottom of the chainring, or that the chain jumps off to the inside of the inner chainring? Those are two separate issues, and the latter isn't really 'chain-suck'.

If the chain is getting sucked up into the chainstay as it tries to come off of the bottom of the chainring, that could be the chain and/or chainrings are worn and need to be replaced.

If the chain is jumping off as you shift to the small (inner) chainring, that is likely to be a matter of front derailleur adjustment.
 

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Discussion Starter · #7 ·
Yep, I already have the crank arm puller. Thanks for the heads-up.

As far as the chain suck, it occurs between the middle and granny cogs. Specifically, when switching into the granny chainring. Hopefully I will be installing the new parts tonight, and test ride tomorrow, so we'll see what happens.
 
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