Rear derailleur fitting problems - Now resolved

[gerryattrick]

Advice wanted on rear derailleur problems please. I’ve just put a Deore XT rear mechanism (M739) and Deore XT M739 shifters (8 speed) on my bike which has a seven speed cassette. The cassette is virtually new and the chain is new. My problem is that changing down (inwards) is fine, but when changing up, often the chain doesn’t move and then on next shift jumps two rings. The shifters seem to be working fine and I believe there is normally not a problem in having 7 speed cassette and 8 speed shifters.

I have some ideas e.g.
1. The cables (new Teflon coated) could be sticking (I used old outers)
2. Could there be a weak spring in the mechanism – it seems to be Ok

Gears have never been a strength of mine so, before spending a lot of time looking for a solution I wonder if anyone can help.


Thanks for the replies. The problem was caused by using an old outer leading into the derailleur. Changed that and hey presto. Luckily I tried that first.

 

[marin man]

Set it up somewhere in the middle of the block so it will shift nicely and then try the other gears as,if the spring is a bit worn in your rear mech this may be enough to get it shifting ok.

 

[urbanfireblade]

Ok, i'll be brave and answer.
Ur using 8 speed shifters with a 7 speed cassette. Did that not strike you as being the problem?
For every click at the shifter a 7,8 or 9 speed shifter pulls the cable 'x' distance, which is exactly what the distance is for the matching 7,8 or 9 speed cassette.

If you use an 8 speed shifter with a 7 speed cassette it will not pull the cable the matching distance between the cassette cogs and therefore will not shift the chain the required distance to select the next cog.

 

[urbanfireblade]

accidently posted twice

 

[marin man]

I was under the impression that eight speed thumbies and seven speed thumbies are one and the same (hidden last click) and seven and eight speed are the same cable pull as well,but maybe I have been wrong all this time,I used to use eight speed gripshift with seven speed cassette no probs :?

 

[the great roberto]

I had to read this twice. Why are you using the seven speed cassette ?
Get a nice m737 cassette and the problem will go away.

 

[urbanfireblade]

Ah you got ME thinking now! Lol, u have the option to not use SIS for now by flicking the small tab lever on the xt shifter.
Certainly 8 and 9 speed isn't compatable with each other, i assumed thats the same for 7 and 8 speed. But then 7 and 8 speed chains are the same width so.......
IDN :cry:

You could always post up a youtube clip of it. Maybe a closeup starting at the shifter and then slowly following it the the rear derailleur. Someone may then spot what is wrong if it isn't the 7/8speed mixing thing.[/quote]

 

[marin man]

Eight speed was an optional upgrade in the early days so you only had to buy a new cassette and everything else was compatible,I have even used ninespeed chainrings with eight speed running gear before with no real problems,it is the rear spacing with nine speed that is different,(and the chain width).I think that everything you are using is compatible it just needs fettling some more......

 

[Iwasgoodonce]

There may be a 0.1mm (ish) difference between 7 & 8 speed. The problem could be the 'angle of dangle' so look at the screw near the drop out. I would work on getting 6/7 indexing fine. The rest should then work too.

 

[marin man]

0.1mm :shock: do measurements that small actually exist :shock: