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 Post subject: Suntour xc pro problems
PostPosted: Thu Jun 06, 2013 7:11 pm 
Gold Trader | rBoTM Winner
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Hi I've just replaced my XT M73x stuff with Suntour XC Pro rear and front mech, hubs, cassette and thumbies

And I have some problems with the rear mech.
The mech cant quite get on the right cog constantly rattling and pedal crank slips on the lower two cogs.
And an insult to injury It shifts from 7 6 5 4 2 then 1 missing out the 3rd largest cog.
Took it to an LBS (admittedly not a great one) and was told that the mech isn't compatible with the shifters or has some problems.

The cassette is 7 speed Microdrive, 9 speed Sachs PC91 chain and as mentioned the shifters and mech are XC Pro (7 sp shifters ) the shifters are in great nick but the rear mech is slightly tatty.

The cassette seems in pretty good order with not much wear at all.

There is no crank slippage when pedalling by hand on a stand - only when pedalling when riding.
What can the problem be??


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PostPosted: Thu Jun 06, 2013 7:29 pm 
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Location: Antwerp, Belgium
That shifting issue sounds pretty much like what my XC Pro mech and cassette are doing when controlled by an XT shifter.
Perhaps your shifter is intended for an Ultra freewheel rather than a Microdrive one. Or maybe there's a problem with the mech itself.

Put the rear shifter in the highest gear, take the chain off the bike (really, just do it) and slowly pull the cable somewhere where it's bare. If there's any friction in certain parts of the mech's range of motion, you should feel it that way.
If there's no friction, it stands to reason that the mech is doing exactly what the cable tells it to do, so you may need to look at the cables or the possibility that you're using 2 different indexes on one bike.

I do have reservations about using a 9-speed chain on a 7-speed cassette, but that's probably just me.


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PostPosted: Thu Jun 06, 2013 7:33 pm 
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7 doesn't go into 9 very well.
The pc91 chain is a narrower chain link than 7 or even 8 speed.


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PostPosted: Thu Jun 06, 2013 7:47 pm 
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As mentioned its the chain. They are narrower than 7 or 8 speed chains.


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PostPosted: Thu Jun 06, 2013 7:51 pm 
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Oh :( I heard that 9 sp chains work well with 7 sp cos it worked like a dream with my 7 sp XT setup before I changed.

So 7 or 8 sp chain?


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PostPosted: Thu Jun 06, 2013 7:58 pm 
Dirt Disciple

Joined: Tue Jan 03, 2012 6:01 pm
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Location: Chicago, IL, USA
The chain should be fine. Narrower chains work fine on older stuff. Its the other way around that can be a problem. 8spd chain with 9 or 10 speed cassette.

I have no problem using a 10spd chain on 7spd Suntour, Shimano, or Sachs rear clusters.


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PostPosted: Thu Jun 06, 2013 7:59 pm 
retrobike rider / Gold Trader
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Its not the most accurate in shifting anyway and I think I will fit a floating top jockey to mine soon, but it should all shift fine. I use a pc850 on my setup.

Carl


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PostPosted: Thu Jun 06, 2013 8:26 pm 
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Hope that helps you out ibbz.


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PostPosted: Thu Jun 06, 2013 8:28 pm 
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Couple other issues
The chain comes off the cassette largest cog and conez off to slip between spokes when shifting to extremes and H L screws make no difference. When switched to F (rather than 7) things are slightly better in middle cogs but still problems persist .

I'm going to replace the xc pro rear with the xt again to check the shifters I have 3 sets of nos xc pro shifters inc 7 8 sp switchable one so may test em later


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PostPosted: Thu Jun 06, 2013 9:02 pm 
King of the Skip Monkeys
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i would look at the shifters - it sounds as if you have a cable pull missmatch somewhere, try just a standard old shimano thumby and a shimano rear mech on the existing microdrive cassette and see if it integrates, the replace the shifter, then the mech until 'something' works or doesnt.

9spd chain is a red herring, they work perfectly well with 8,7,6 etc as already mentioned.


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