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Replacement drivetrain for an 80's mountain bike

Old 03-14-08, 09:01 AM
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Replacement drivetrain for an 80's mountain bike

My LBS was looking over my 20-year-old Mountain bike, and the entire drivetrain is shot. They shortened the chain to get me by until I can afford to replace it all. I'm not even sure what the questions are here, let alone the answers...

I'm hoping to get this done soon, before a week-long tour The Historian and I have planned, soit's time to start pricing things out. Those of you who tour on a MTB, do you have any thoughts on what types of components I should get? It's an 18-speed bike with 6-gears on the rear wheel and a triple chainring up front.

Not sure if I'll need to replace the deraileurs, but I'd guess at least the gears in the rear one if not the whole thing, since the teeth are all pretty worn.

Thanks!
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Old 03-14-08, 09:18 AM
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First, I'd ask the question whether you wish to replace worn bits on your drivechain, or if you wish to replace your drivechain. There are 6-speed bits still around, but they won't be getting any easier to get.

It sounds to me like you'll need a new rear freewheel (ebay that one, I got one for about $10 nos). You can use an 8-speed chain quite happily (I like SRAM ones, let's say $25). It will be unusual that your rear derailleur has worn out -more likely just the pulleys; you may be able to get replacement pulleys from ebay or your LBS. Assuming you just buy a new rear derailleur, Nashbar has the Shimano Alivio at $17. Even though it's meant for 8 speeds, there shouldn't be any problems. The final issue you have is replacing your chainrings..... of course it might not be economical to do so. Surprizingly, it can be cheaper to get a replacement crankset. Assuming you have a square taper, the Sugino XD300 at around $60 is good value or there are Shimano Deore/LXs around, just that you might need a new bottom bracket if you go that route.

Since it sounds like that drivechain is quite old, I'd recommend replacing everything, as a worn chain can wear out new freewheels more quickly, a worn chainring can wear out a new chain quickly, etc, etc.

Or you could simply replace your drivechain with a new one. Caution here though -it will be as expensive or more so as it will probably necessitate not just all of the above (maybe a cassette rather than a freewheel) but also new shifters and probably hubs as well, and will be expensive.
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Old 03-14-08, 10:07 AM
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I'd call up Harris Cycles, they deal with a lot of older bikes.

Also, it's a bit unclear on what exactly is wrong. Is the rear derailleur shot? Front derailleur? Chain worn? Chainrings worn? Is the bottom bracket also out?

Chain, chainrings should be easy to replace. Rear derailleur should be replaceable, via eBay if nowhere else.
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Old 03-14-08, 11:52 AM
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Unfortunately, the chainrings are worn. Is it possible to get a replacement drivetrain kit, or do I look for components? Sorry I'm being so clueless here, I'm usually more mechanically ept.
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Old 03-14-08, 12:39 PM
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Originally Posted by neilfein
Unfortunately, the chainrings are worn. Is it possible to get a replacement drivetrain kit, or do I look for components? Sorry I'm being so clueless here, I'm usually more mechanically ept.
Your looking for components, now there are issues, if your crank is bolt together, where the rings are held on with several bolts, then you can replace the rings only. If it's not held together with bolts, then you need to replace the crank. Replace the bottom bracket if it's a cartridge type, or rebuild it if it's cup and cone. While the BB may not need to be done, it's easier and cheaper to do this when it's all ripped apart already. Then to rip it apart to replace the rings, and then after your tour, when the BB is all crunchy, rip it all apart again to do the BB.

The tricky bits are the cassette/freewheel, as 6 speed parts may be tricky to find, you may need to move to 8 speed parts, and that means replacing the right shifter and possibly the rear dérailleur as well, Once you get to that point, it may be more cost effective to look at replacing the bicycle, epecially if your paying the LBS to do the work.
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Old 03-14-08, 01:20 PM
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I'm allocating around $200 for this.

6-speed Freewheel/ Cassette: $35
Triple Chainring: $60
Chain: $15

Keeping to this budget will give me some room so that if I do need to replace the bottom bracket or bits of the rear deraileur, I can. If they're in good shape, I can spring for better components for the drivetrain.
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Old 03-14-08, 03:52 PM
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At Nashbar :

X Nashbar Basic Mountain Crank Set. NS-CMC $34.99
X Nashbar Sealed Cartridge Bb NA-SBB 115X68 $14.99
X Nashbar 7/8 Speed Chain NS-CN78 $9.99
X Shimano Deore Rear Derailleur SH-RDM510A $17.99
X Nashbar 6 Speed Freewheel NS-FW6 14X24 $14.95
Subtotal: $92.91

If you need front derailleur, that would add another $20 for the Shimano LX version.

If you plan to continue use of this frame, you may consider upgrading the wheels, or at least the rear wheel, to a cassette hub, go with 8, 9, or 10 speed cassette, and get new shifters. That would increase price another $150 to $200.
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Old 03-14-08, 04:36 PM
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Originally Posted by bwgride
At Nashbar :

X Nashbar Basic Mountain Crank Set. NS-CMC $34.99
X Nashbar Sealed Cartridge Bb NA-SBB 115X68 $14.99
X Nashbar 7/8 Speed Chain NS-CN78 $9.99
X Shimano Deore Rear Derailleur SH-RDM510A $17.99
X Nashbar 6 Speed Freewheel NS-FW6 14X24 $14.95
Subtotal: $92.91

If you need front derailleur, that would add another $20 for the Shimano LX version.

If you plan to continue use of this frame, you may consider upgrading the wheels, or at least the rear wheel, to a cassette hub, go with 8, 9, or 10 speed cassette, and get new shifters. That would increase price another $150 to $200.
The rear wheel is practically new, so I'll just replace the freewheel/ cassette.

The cranks are fine, I think. (If they're not, the freewheel is probably pretty grungy as well.)

I think I'll stick with 18 speeds if I can, I'll go to 21 if I can't find the right parts.
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Old 03-14-08, 04:42 PM
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80's MB means 126mm spread vs 135 mm in modern MBs. All new MB wheels come in 135mm, you can get a road hub (130mm) and squeeze it in or pry appart your bike's ass end. I believe Sheldon has it, look for "cold setting".

I just got a pair of old identical Miyatas for peanuts this week.

I'll leave one as is and play with the other... ...9 speeds are good.

Just remembered ! Harris has some old Shimano 7 speed freewheels in stock, get one of them and a cheap shifter.
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Old 03-14-08, 09:04 PM
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Originally Posted by xiaodidi
80's MB means 126mm spread vs 135 mm in modern MBs. All new MB wheels come in 135mm, you can get a road hub (130mm) and squeeze it in or pry appart your bike's ass end. I believe Sheldon has it, look for "cold setting".
Eh, don't worry about that much. You're talking about a few millimeters. Spread those babies out, drop the wheel in, and it should center itself fine enough. Been there, done that....
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Old 03-14-08, 10:03 PM
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Dare I suggest it, but if you go to the bicycle section of Walmart, you will likely find a 6sp freewheel (which I suspect is what would have been on an 80s MTB), and possibly a 6-7-8sp chain, and maybe even a replacement chainring set (admitted riveted, but probably little different to what you had as original equipment on the bike). Also get some cables while you are there. Probaby cost you about $50 all up.

Likely also you have a ball-and-race BB that just needs cleaning and repacking and adjusting.

Of course, you do need the tools. The most obvious specialised one will be the freewheel remover, then the chain tool and the crank-puller. If your BB is a cartridge type, and its knackered, you'll need a tool for that too.

If you can do that yourself, fine.

If not, hand the job over to an LBS. Mind you, I would be concerned if an LBS told me it had temporarily fixed drivetrain wear by shortening the chain. That's a load of smelly baloney and would be laughed out of the Bicycle Mechanics Forum. So, probably find another LBS that won't feed you a line of rubbish and will do the job properly.
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Old 03-15-08, 12:58 AM
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My 1990 Trek 800 mountain bike had a 6 speed freewheel and a biopace crank that I didn't like. The shifters, FD and RD are Exage Country (see the specs from the Trek 1989 catalog). Anyway, I was able to replace the crank with the Sugino XD300 (46-36-26) and the freewheel with a 7 speed new Shimano 14-28 freewheel. It was necessary to change the bottom bracket but I was able to keep the derailleurs and shifters. I had previously tried a megarange freewheel, but I didn't like the jump from 24 to 34. Anyway, there are also some new freewheels by IRD that Rivendell sells that are 6 speed and 7 speed that have even spacing up to 32 teeth ( I think, check their website). There were some first generation new IRD freewheels that had some quality control issues and were taken off of Harris and Rivendell's websites for a while, but Rivendell says that IRD worked on them and fixed the quality control issues. As for going from 6 speed to 7 speed, the only issue that I'm noticing is that when my thumbshifters are in SIS mode, some gears seem a little off-centered. But, fortunately, there is a friction option that I use and then the shifting is fine.

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Old 03-15-08, 11:12 AM
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Originally Posted by Rowan
Mind you, I would be concerned if an LBS told me it had temporarily fixed drivetrain wear by shortening the chain. That's a load of smelly baloney and would be laughed out of the Bicycle Mechanics Forum. So, probably find another LBS that won't feed you a line of rubbish and will do the job properly.
Oh, they never said they were fixing the problem. I asked them what they could do to get me through the next few weeks until I could afford to replace things.
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Old 03-15-08, 11:20 AM
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Originally Posted by neilfein
My LBS was looking over my 20-year-old Mountain bike, and the entire drivetrain is shot. They shortened the chain to get me by until I can afford to replace it all. I'm not even sure what the questions are here, let alone the answers...

I'm hoping to get this done soon, before a week-long tour The Historian and I have planned, soit's time to start pricing things out. Those of you who tour on a MTB, do you have any thoughts on what types of components I should get? It's an 18-speed bike with 6-gears on the rear wheel and a triple chainring up front.

Not sure if I'll need to replace the deraileurs, but I'd guess at least the gears in the rear one if not the whole thing, since the teeth are all pretty worn.

Thanks!
You have ten weeks until the tour.

I can't speak for Neil F.'s drivetrain, but the frame appears to be in good shape. The bike is great for loaded touring, and I hope it can be restored and upgraded.
 

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