Rear Derailler help needed.

[The Fitter]

I have a Dawes super Galaxy that needed a new cassette. The old one was a 12-28t and the new one i fitted was an 11-36t. After fitting the new cassette i found that the top pulley wheel on the dérailleur was hitting the 36t sprocket on the cassette. i bought a new dérailleur ( Deore XT RD-M786 sgs 10 speed) and fitted it, but i wont change up to the top gear. I done the indexing and that seems to be ok, when i push the dérailleur over with my thumb it goes over to the top gear (36t sprocket). It seems to miss a couple of gears when i change up using the shifter, and only goes up 8 gears. Have i bought the wrong dérailleur, or have i done something wrong.
Any help would be appreciated. Thanks in advance.

 

[raleighnut]

Not sure but it sounds like you have a cable pull issue, some MTB mechs run a different pull ratio than road mechs but without the tech docs it's hard to tell if yours is compatible.

 

[accountantpete]

The problem will be the spacing on the new cassette rather than the new mech.

Have a google re this little gadget https://www.sjscycles.co.uk/cables/jtek-shiftmate-6/

I'd email them with your shifters/rear mech/cassette details to see if will work.

 

[gazza1286]

The gear cable is attached to the rear derailleur incorrectly.

Disconnect the cable then press the upshift lever repeatedly (as if going down the cassette to smaller sprockets) whilst holding onto and pulling the inner cable. You will find that this releases some cable. Repeat until the shifter thinks it's in the highest gear. Then reconnect and index. The shifter will now move the full width of the cassette. Adjust the limit screws as you shouldn't be able to manually push beyond the 36t.

 

[boydj]

From various posts on here in the past, I believe that the Deore mech needs to be 9-speed to work correctly with a 10-speed road shifter due to different pull ratios used in road and x/c mechs.

 

[The Fitter]

Thanks for your posts and the advice given. Sorry for the delay in replying. I have decided to put the same size cassette back on, as it seems a lot of hassle to change the setup.

 

[Elybazza61]

From various posts on here in the past, I believe that the Deore mech needs to be 9-speed to work correctly with a 10-speed road shifter due to different pull ratios used in road and x/c mechs.

Yep,I run a 9-speed Deore with my 10-speed 105 shifter;still can be a fiddle to get it to shift ok though,cable tension and routing has to be just so.