Been meaning to fix my MTB for a while now. The gears on the rear started jumping around a bit, but to be fair, the cassette had been on for four years, so well overdue a good service.

Bought new cassette, chain and jockey wheels. Shortened chain to correct length, installed…

And no matter what I do the gears are still missing one or two altogether, jumping straight up to the next one.

I’m not new to fixing bikes by any means. It’s something I’ve always done to some degree since a small child, and I have indexed many gears with varying successes. Being a tight arse however, rarely do I work with a full suite of new parts, and I do often expect one or two gremlims -perhaps because of which, I’ve never been 100% happy with any gears I’ve ever indexed. Like ever.

Is it really that difficult? Or that easy to do wrong? Or is it more likely component issues (bent deraileur for example)?

Any tips, please?

Shifters and mech are matching Sram X-7, which came with the bike new. And I’m not sure it’s relevant but it’s also sticking occasionally in the lowest gear, and won’t release without a little persuasion, despite the cable releasing.

Could be sticky cables.

If they aren’t free enough in the housings it may not immediately release on an upchange.

Cables could possibly be very slightly sticky…

New cable outers and inners if it’s a few years old and start from scratch.

Sort the hi low adjustment.
Attach the cable.
Select the second from top gear (second smallest ring), use the barrel adjuster to make sure the chain runs on that cog nice and smooth and shifts up and down to the next cog without hesitation.

Roberts ya fathers brother.

New cables are a must.

There is a guide on the park tools website. I have found it very good. Generally if I follow those steps and it isn’t working then there is something bent.

Or bent hanger or mech.

Well I guess the cheapest and most sensible option is to try some new cables.

Any thoughts on the mech sticking in the lowest (1st) gear? There is tonnes of slack in the cable when it does it, it’s literally hanging.

Did you replace chainrings OP…?

Chainrings up front remain the same.

There is no dark art. It took me years to work that out.

SRAM Mech setup
Check Hanger
remove cable from mech
remove chain
Set high & Low limits by eye by pushing the mech over to full travel and adjusting the limit screw then do the low.
Put chain in
let all cable out and connect it
Run it through the gears and see how you get on – the sound basis should help.
Look at the b-limit screw to keep the mech in the right place.

If this fails then cables might be next, try flushing the lines out with some gt85 or similar as a first step.

If your woes continue I would suggest either a mate who knows or LBS. Get them to do it when your there and tell/show you whats going on.

4 years old… I’d be amazed if it did not need new chain rings too. It will probably slip under load

Hanger may be bent very slightly
Replace cables and outers

Indexing should be simple. If it isn’t then something is wrong

Definitely sounds like knackered cables. Mine were wrecked within 4 months because of the mud.

I went to Afan and I got about 3 miles from the end and was stuck on both front and rear mechs.

only other thing I can add is, if it was a cheapish bike when new, have you bough a nine speed cassette for 8 speed shifter? X-7 also come in 8 speed, worth double checking.

If you’ve ridden a fair amount, your X7 mech is likely to have a fair amount of slop in it which makes it much harder / impossible to index the gears properly.

Make sure the mech is bolted on tightly and then pinch the bottom of the cage with your fingers. Move it side-to side (towards the wheel <-> away from the bike), if there’s more than about 1.5cm of movement then I’d be adding a new mech to your shopping list too.

Try the simple stuff like cables first, though.

If you’ve got the right shifters and nothing is bent it’ll be the cables. SP41 highly recommended

From the OP:

despite the cable releasing.

So you’ve got slack in the cables but the mech isn’t moving? Sounds like a seized mech/spring perhaps rather than cables. Give it a good clean, soak it in lube, and work it with your hands to loosen it up, then try it.

I’ve not had it with a rear mech but it happened once with a front mech and I ended up replacing it.

So you’ve got slack in the cables but the mech isn’t moving? Sounds like a seized mech/spring perhaps rather than cables. Give it a good clean, soak it in lube, and work it with your hands to loosen it up, then try it.

It’s strange. It’s only doing it in first gear. Moves through all the others fine (sometimes a little too enthusiastically, hence the thread). Move it into first and it stops there.

The bike hasn’t been ridden for a few months mind. The derailleur was cleaned and lubed, but I’ll give it a going over to make sure there’s no stiffness in it.