7 speed cassette conundrum

[stalagmike]

I recently bought a cheap and old (2000s?) GT avalanche 1.0 for my teenage son and have been getting it roadworthy for him. I changed the cables, tyres, pads etc. but for the life of me I could not get the gears to index properly. Then last night I noticed it has a 9 speed cassette but only a 7 speed shifter! So the question I have is, do I :-

1. Fit a 9 speed shifter
2. Fit a seven speed cassette
3. Leave it and just put up with a not being able to select all 9 gears and a small amount of chain rub at the front?

I understand the current chain is probably ok as that would be 7-9 speed anyway. My instinct says get a new cassette and chain anyway, but just thought I would put it out the hive mind.

 

[Big John]

New chain and 7 speed cassette. I work on bikes that have got a multitude of mixed bits so what you've discovered on that bike is pretty normal at the bike charity where I work. Just make sure you've got Shimano changer and rear mech (or SRAM and SRAM). I tried mixing those at work in my innocence only to discover I'd still be there now and they wouldn't work. Chain and cassette and you'll be fit to go.

 

[fossyant]

I buy 8 speed cassettes and drop one of the sprockets for my 7 speed commuter. Just use an extra spacer on the freehub.

 

[Cycleops]

We're all different and I'm sure you'll get people voting for all three. For me I'd go with a 9 speed shifter to use all those previously unused gears.
What would your son prefer? He's the one who's got to use it.

 

[matticus]

I buy 8 speed cassettes and drop one of the sprockets for my 7 speed commuter. Just use an extra spacer on the freehub.

That may well work "OK" for you, but the pitches between gears is different:

Cassette or Freewheel	Sprocket Pitch	Code
	(mm)
All modern 5 and 6-speed	5.50	S5/6
All standard 7-speed	5.00	S7
Campagnolo 8-speed	5.00	C8
Shimano 8-speed	4.80	S8
Campagnolo 9-speed	4.55	C9
Shimano 9-speed	4.35	S9

(As you can see, 9sp is quite a big difference.)

EDIT: if you can get a CAMPAG 8sp wheel+cassette cheap enough, that would work too! :P

 

[Ajax Bay]

The shifters that are fitted (properly) to this bike are ST-M510 Deore
https://bike-rep.ru/images/PDF/ST-M510.PDF
Think a 9sp RH shifter will work out cheaper than a 7sp cassette, a spacer, and a 7sp chain.
Here's mine (also potentially for a son!). I too am having problems sorting out the shifters: I've got 8 clicks but there's no tactile or audible feedback.

 

[stalagmike]

The shifters that are fitted (properly) to this bike are ST-M510 Deore
https://bike-rep.ru/images/PDF/ST-M510.PDF
Think a 9sp RH shifter will work out cheaper than a 7sp cassette, a spacer, and a 7sp chain.
Here's mine (also potentially for a son!). I too am having problems sorting out the shifters: I've got 8 clicks but there's no tactile or audible feedback.
View attachment 731652

Nice! I will look for both shifter and cassette and weigh them up. I also have to work out why the shocks don’t lock. Any advice on fixing those appreciated. They are suntour xc-pro from the stickers

 

[Ajax Bay]

Super pleased you posted this. I had lacked perseverance to resolve the shifter but taking it apart and giving it a good clicking and dousing seems to have done the trick and I now have a cable driven RD to get all 9 sprockets back in action.
Shocks: not me guv. Mine are Rock Shox Judy TT. They work.

 

[Sharky]

Would a friction lever be an answer?

 

[cyberknight]

The shifters that are fitted (properly) to this bike are ST-M510 Deore
https://bike-rep.ru/images/PDF/ST-M510.PDF
Think a 9sp RH shifter will work out cheaper than a 7sp cassette, a spacer, and a 7sp chain.
Here's mine (also potentially for a son!). I too am having problems sorting out the shifters: I've got 8 clicks but there's no tactile or audible feedback.
View attachment 731652

Depends obviously how worn the cassette and chain are worn I think ?

 

[Cycleops]

Would a friction lever be an answer?

Yes, you he could use one of those cheapie friction Shimano thumb shifters.



This pair of vintage ones are £20 on the EvilBay.
Still make them I think but not so cheap now

 

[stalagmike]

Depends obviously how worn the cassette and chain are worn I think ?

I’ve lost my chain tool but I’ll check when I find it. If I change cassette I would do the chain too anyway

 

[fossyant]

That may well work "OK" for you, but the pitches between gears is different:

Cassette or Freewheel	Sprocket Pitch	Code
	(mm)
All modern 5 and 6-speed	5.50	S5/6
All standard 7-speed	5.00	S7
Campagnolo 8-speed	5.00	C8
Shimano 8-speed	4.80	S8
Campagnolo 9-speed	4.55	C9
Shimano 9-speed	4.35	S9

(As you can see, 9sp is quite a big difference.)

EDIT: if you can get a CAMPAG 8sp wheel+cassette cheap enough, that would work too! :P

It works. Ran two bikes this way for years until I upgraded one to 8 speed. 7 speed spacers are 3.1mm, 8 speed 3mm. Sprockets same thickness. At worse you are 0.3mm out which is easily taken up by the jockey float and of course hi and lo limit screws. Works perfectly with STI shifters.

Done because I don't need any more gears on the vintage MTB and want to keep it as period as possible.

It's a cheap option and if wanted you could reuse the 7 speed spacers. 8 speed cassettes are a little more readily available and in more gear ranges.

 

[Ajax Bay]

Depends obviously how worn the cassette and chain are worn I think ?

Guess so, but most of these bikes have not been ridden much so I suspect the chain and cassette have got 1000s of km to go. They're 9sp and the economics of swapping out the chain at (say) 2500km is marginal: as opposed to letting them grow old/worn gracefully together.
For @Sharky Have you had success with a flat bar friction lever operating a 9sp cassette?
For the OP: the shifter I've referenced is a brake/shifter combo: I don't know what 7sp aberration someone has fitted on the bike you've bought.
For the OP: Your Option 3 will cause nause as the shifting will be poor: I would be embarassed to offer my son a bike where the gears don't work properly. Sure fire way for him/them not to ride the bike.

 

[stalagmike]

Friction lever would be tricky because the current set up is a brake/gear combo. But not impossible I guess.