Martin Reynolds Posted August 17, 2012 Report Share Posted August 17, 2012 I'm doing up a friends mountain bike and having a bit of an issue with the rear gears. I've fitted a shimano deore XT rear mech with a Shimano deore LX 9 speed shifter. However the rear cassette is 7 speed, and the hub can only take a 7 speed cassette. So two questions : 1. can i get away with just changing the shifter? And use something like this? http://www.ebay.co.uk/itm/290752684619?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_2364wt_1236 2. As it's set up atm, the chain jumps on 3-7th gear. I know its not gunna be perfect with it's current set-up, but it seams the chain is jumping around the teeth, rarther than up or down. I.e, the rear mech is perfectly inline with the gear when it skips. Cheers Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted August 17, 2012 Report Share Posted August 17, 2012 Chuck on a shifter to match the cassette and the mech will work fine - the reason it'll be skipping is most likely just due to the fact a 9spd shifter won't be pulling enough cable and so won't be shifting the mech across far enough to sit in the centre of the sprocket. That Altus on eBay should do the job. For the skipping, if it's not simply due to the shifter/poor setup issue it'd be worth checking for stiff links etc. This is all assuming that the chain's not worn/stretched, of course? Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 17, 2012 Author Report Share Posted August 17, 2012 Chuck on a shifter to match the cassette and the mech will work fine - the reason it'll be skipping is most likely just due to the fact a 9spd shifter won't be pulling enough cable and so won't be shifting the mech across far enough to sit in the centre of the sprocket. That Altus on eBay should do the job. For the skipping, if it's not simply due to the shifter/poor setup issue it'd be worth checking for stiff links etc. This is all assuming that the chain's not worn/stretched, of course? Brand new 7 speed chain. I know chains are meant to 'wear' into cassettes, but i've always taken that with a pinch of salt to be honest. I'm gunna get that shifter before looking into it further anyway. Just wanted to make sure, as i know some shifters/mechs have different ratios, i think its SRAM that has 2:1 ratio? Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted August 17, 2012 Report Share Posted August 17, 2012 Shimano are (all?) 2:1, SRAM are (mostly) 1:1 Quote Link to comment Share on other sites More sharing options...
Tomm Posted August 20, 2012 Report Share Posted August 20, 2012 7 Speed is really old - are you sure that's what it's got? Has the freehub body got a plastic spacer on it? If so, you might be able to take that off and stick a normal 8 or 9 speed (or 10 spd) cassette on there, that would be the best plan. Alternatively, buy a 9 speed cassette and take one or two rings off so it fits on the freehub body. Cheaper cassettes (E.g. SRAM 970 or Deore rather than SLX/XT) will allow this as the bigger sprockets are separate, not on an aluminum carrier. You may have to drill out the connecting bolts but that's easy enough. 7 and 8 speed both have the same distance between sprockets and same chain width/pitch, so an 8 speed shifter simply has an extra 'click'. If you set up an 8 speed shifter properly and do the limit screws, you should be able to make it work perfectly with a 7 speed cassette. I'm not sure on cable pull ratios, but all Shimano 7/8/9 shifters will all pull the same amount of cable for a given movement in the rear mech. 10 speed has a different cable pull ratio. To answer your questions: 1. Yes, or as above you could get an 8 speed shifter (might be easier to find a decent one) 2. The chain skipping will be a problem of the chain + cassette mismatch. Depending on how knackered the cassette is, they *might* end up working together properly once you've run them in a bit. However, instead of spending a decent amount of money on really outdated 7 speed stuff, I'd recommend spending £20-30 on a back wheel that can take an 8/9/10 speed cassette and bring the bike into the 21st century Chuck on a shifter to match the cassette and the mech will work fine - the reason it'll be skipping is most likely just due to the fact a 9spd shifter won't be pulling enough cable and so won't be shifting the mech across far enough to sit in the centre of the sprocket. This is not quite right. The 9 speed shifter will move the derailleur fully across a 7 speed cassette, no issues there. Obviously the indexing will be off, although that makes less difference than you might imagine. On my DH bike I've been running a 9 speed shifter with 8 speed cassette and chain for ages and there's (surprisingly) never any skipping/etc. The indexing is useless but I can use all the gears. This would probably annoy me on my XC bike, but on the DH bike it's not an issue. Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 21, 2012 Author Report Share Posted August 21, 2012 Sorry, properly should expand. It is 7 speed, i may be Cornish, but i can count It's an old mountain bike which im doing up for a friend, but trying to do it cheap. I've fitted the Altus shifter, and the indexing is spot on, however it's still slipping on the lower gears (3-7, worse on the lower gears). I think its a mixture of the mech spring being weak, and using a new chain on an old cassette. Does using old/new gear together cause this much of an issue? Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted August 21, 2012 Report Share Posted August 21, 2012 Can do if the sprockets on the cassette are particularly worn. Are they? Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 21, 2012 Author Report Share Posted August 21, 2012 I'll try and get pictures up later, but they don't look worn, the teeth still have the correct square edges. Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 21, 2012 Author Report Share Posted August 21, 2012 Picture of cassette Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted August 22, 2012 Report Share Posted August 22, 2012 It's f**ked, replace it But seriously, some pretty worn teeth and looks like it's been left in a canal for an age - get a new one on there. Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 23, 2012 Author Report Share Posted August 23, 2012 Thats like one day's rain in cornwall Hint taken, ordered a new one yesterday Quote Link to comment Share on other sites More sharing options...
ross87 Posted August 25, 2012 Report Share Posted August 25, 2012 Also in that picture you posted the top jockey wheel of the mech is too far away from the cassette which will add to the shifting problems. Try undoing the tension screw on the mech to move the jockey wheel closer to the mech. Hope this helps Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 25, 2012 Author Report Share Posted August 25, 2012 Not one bit New rear cassette arrived and fitted, it was about 80% working. Still had issues with the rear mech, theres bugger all tension so i think the springs on its way out. Found an old mech and fitted it, just need to dial it in, but i got rained out today Quote Link to comment Share on other sites More sharing options...
bike_dummie Posted August 25, 2012 Report Share Posted August 25, 2012 Isn't that chain too long and needs to be shortened as the deralieur should be closer to a straight line then an L shape presuming it is on the largest chainring upfront. Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 25, 2012 Author Report Share Posted August 25, 2012 Isn't that chain too long and needs to be shortened as the deralieur should be closer to a straight line then an L shape presuming it is on the largest chainring upfront. I've taken one link out since that picture,i dont think it was on the largest front chainring Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted August 26, 2012 Author Report Share Posted August 26, 2012 With a new rear cassette, and taking two links out of the chain, it seam's spot on. Thanks for everyone's help, cheers guys 1 Quote Link to comment Share on other sites More sharing options...
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