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old MTB drivetrain compatibility knowledge (Read 5047 times)

nic mullin

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I've got an old (late 90's vintage) MTB that needs some TLC - chainrings are worn out and the chain slips when I stamp on the pedals. I'm guessing that the chain is also worn and won't play well with new chainrings, so planning to replace the chain and cassette too.

The chainset is an old Shimano LX one, like this:



Anybody know whether I'll be able to buy compatible chainrings? In particular the big ring is riveted onto the spider, I can't seem to find any big rings that even look like they might fit online. Do I need a whole new chainset? The cranks and BB are fine.

If the latter, most cranks (apart from low end ones) seem to now be hollowtech not square taper. The frame (GT Zaskar, 1997) has a 73mm width internally threaded BB shell and uses a front mech that is cabled from the bottom - will a hollowtech BB fit in this BB shell, or has the standard size/threading changed? If it will fit, will the chainline be the same, or will I need a new front mech to cope?

8 speed cassettes seem to be readily available for cheap, I'm assuming nothing's changed there?

Chains seem to be a bit of a nightmare - Shimano and KMC chains always had a terrible rep back in the day, Sedis don't seem to make bike chains anymore, what do people use nowadays? Are SRAM chains compatible with Shimano stuff now? Will newer chains designed for 9/10/11 speed be happy on an 8 speed setup?

Apologies for all the dumb questions - I've been out of the loop bike-wise for a long time and am so unfamiliar with who makes what and what's compatible with what that googling just confused me more.

Thanks in advance for any knowledge you can share!

bigtuboflard

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A couple of answers to your questions though not sure of all of the compatibility issues;

1. the old Deore LX chainset I seem to remember didn't have a replaceable big ring as you say, it was riveted on as they tend not to get as much use as the middle and small ring. You can get a pretty cheap replacement with something like this http://www.chainreactioncycles.com/shimano-acera-m361-triple-chainset-square-taper/rp-prod106885

2. square taper bottom brackets are still pretty easy to come by, a quick search on Chain Reaction found these Shimano ones http://www.chainreactioncycles.com/shimano-un55-square-taper-bottom-bracket/rp-prod71369. I'd be inclined though as you say to perhaps look at a new chainset with a new bottom bracket. I don't expect it should affect chain line too much but might be worth reading up on the specs as sometimes the external bottom brackets push the chainline outwards.

3. You can still get 8 speed cassettes but if your chain is slipping as you describe it might be that the free hub is also shot, have you taken the cassette off and had a look at it properly? You'll not be able to run a 9 speed cassette on the same free hub so will have to stick to 8 speed. Also, you'll need to stick to a 7/8 speed chain as they are wider than 9 (or more) speed chains due to the gap between sprockets being narrower on higher speed cassettes. Also the throw on your derailleur and shifter will be specific to 8 speed so you'd have to probably replace them too. SRAM chains on Shimano kit works fine BTW.

4. Look at replacing the jockey wheels on your derailleur too as they'll be worn and will only cause running problems on a new drive chain.

5. Have you thought about taking it all to the local bike shop? They should be able to solve all of the compatibility questions and give you a price. They will of course probably expect you to then spend the money with them; it doesn't go down to well in the LBS to then start haggling based on what you can get on the web by way of comparison.

thekettle

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If you're wanting to keep it reasonably cheap, a full chainset (BB, cranks, chainrings) would be the cheapest way to sort out the front end, plus a 7/8 speed chain and 8speed cassette and you're sorted. Deurallieurs/shifters are likely to be fine, if in any doubt visit the LBS before you spend anything! An external BB will work on your 73mm shell, most modern shells are 68mm and use 2x2.5mm spacers to allow tweaking of the chainline. Square taper BBs are still readily available.
9/10/11 speed chains and chainrings will work on an 8 speed setup, but wear faster, be less durable and shift less cleanly.

bigtuboflard

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If you're wanting to keep it reasonably cheap, a full chainset (BB, cranks, chainrings) would be the cheapest way to sort out the front end, plus a 7/8 speed chain and 8speed cassette and you're sorted. Deurallieurs/shifters are likely to be fine, if in any doubt visit the LBS before you spend anything! An external BB will work on your 73mm shell, most modern shells are 68mm and use 2x2.5mm spacers to allow tweaking of the chainline. Square taper BBs are still readily available.
9/10/11 speed chains and chainrings will work on an 8 speed setup, but wear faster, be less durable and shift less cleanly.
I'd still change jockey wheels though as they should only cost you a few pounds. Anything that has the chain running on it is worth replacing all the same time if everything else is badly worn.



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nic mullin

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Awesome, thanks guys.

Was a bit wary of taking it to the LBS knowing nothing - it'd be too easy to up-sell me on shiny things! Now I've got a feel for what needs doing that'll be my next port of call. More than happy to spend my money local - I'm a punter/pootler and my bikes tend to go many years between getting proper attention, the knowledge and immediacy is more than worth the few extra quid to keep me pootling for the next decade.

Freehub is a good shout - it's definitely not as clicky as it once was and I need to pull the rear hub apart, replace the bearings and repack it, so might as well replace the feehub body while I'm there. Jockey wheels also - they're only plastic and have been around the block a few times.

Mechs and shifters are indeed fine, and the shifters are built into the brake levers (v brakes, no mounts for disc brakes on frame or wheels) so I'll be staying 8 speed if at all possible to avoid opening that can of worms.

Good to know that 9/10 higher speed chains will work if need be, will get an 8 speed one if they behave better and last longer. Any thoughts on chain brands - do Shimano chains still have a rep for snapping, stiff links and need a different, fatter pin whenever you join them?

Thanks again for the knowledge, much appreciated.

bigtuboflard

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SRAM chains with powerlink seem to be up to the job, I've been running one on my singlespeed which gets a fairly tough workout and lots of torque and no problems so far. Presume you can get them in 7/8 speed. Powerlink makes taking the chain off for a soak in degreaser a lot easier too every once in a while.


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nic mullin

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Brilliant, cheers!

Jim

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I'd be wary of what the bike is worth and how much you need to spend on it (unless of course you have an attachment to it that goes beyond its financial value) as it's quite likely it might be better value to buy a 2nd hand bike to replace it

Schnell

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Looking at the picture of the chainrings they don't look very worn to me, though it's a little bit hard to see on the middle ring. Teeth on old chainrings go all obviously pointy and curved, like shark's fins, when they're worn. Which means it'd almost certainly be perfectly fine just to replace the chain and cassette and leave the rest. If a chain is ever slipping on any bike it's almost always chain and cassette rather than chainrings.

steveri

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Good to know that 9/10 higher speed chains will work if need be, will get an 8 speed one if they behave better and last longer.

Not sure about that bit - 10 speed chain will be too narrow for an 8 speed cassette surely? No problem putting 9/10sp rings on an 8 speed setup.
I think those LX chainsets had an integrated spider/big ring which WAS replaceable but no clue if still available. New chainset probs simplest solution. Mind you big ring doesn't look too bad.

Try new cassette and chain first? Then work out if still slipping it's just in certain rings?

You might bring the freehub back to life by taking it off and chucking it in a jar in some light oil - easy enough to try, it's just a big allen key. Saves the risk of exploding freehub and crucial bit flying off behind the fridge scenario :)

nic mullin

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Thanks for the info guys - to clarify, the pic isn't of my chainset, it's just an image off google - mine is very worn and the teeth are almost hook shaped on the load-bearing side. Might be worth trying  a new cassette and chain first though - can't do any harm.

Good point about the value of the bike- I'm pretty attached to it and don't need anything better, but if finding compatible parts becomes more of a problem replacement could well be an option. I'm guessing you get quite a lot of hardtail for your money nowadays.

bigtuboflard

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If you choose to go for a new bike you could always try and sell the bike or frame on here http://www.retrobike.co.uk/forum/viewforum.php?f=2


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thekettle

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Regarding chain brands, my experience is that Shimano chains are still the snappiest, Sedis (they were amazing!) i think got bought out by Sram over 10 years ago. Sram and KMC chains are apparently made in the same factory, and are much tougher than Shimano, with no compatability issues.

nic mullin

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Wow, a quick look through retrobike takes me back, amazing! I think I'm probably too sentimental to sell, and it's probbably too beaten up for anybody to want, but it might be quite rare now (it's one of the bright yellow powder coated ones - I got it cheap as they were so garish nobody would be seen dead on one even in the 90's). I've also got an old BMX that I'm really attached to but needs quite a few bits replacing - I'll be scouring that site for parts when the time comes.

Interesting to hear about chains. I remember not having a spare pin for a Shimano one and having to rejoin it 5 or 6 times as it kept snapping while I tried to ride back home after a long day out in the rain sometime in the mid 90's. Avoided them ever since. Tried KMC but found they rusted a lot, Sedis all the way after that.

Thanks again for the info, ordered a few bits of chainreaction, off down the bike shop for the rest at the weekend.

 

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