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-   -   Replacement for lost guide pulley, Shimano STX 7-speed (https://www.bikeforums.net/bicycle-mechanics/1241838-replacement-lost-guide-pulley-shimano-stx-7-speed.html)

nathand 11-06-21 06:54 PM

Replacement for lost guide pulley, Shimano STX 7-speed
 
I have a 1996 Trek 930 I use with a kid trailer. While towing my son to tennis this week, the upper guide pulley fell off the derailleur, including the bolt. It's a 7-speed Shimano STX. Thoughts on how I should fix this? I found replacement pulleys at my LBS that aren't a perfect match but were cheap enough ($3) to give them a try, but the shop didn't have a bolt long enough to hold it in place. Is it worth searching for a bolt to fix this derailleur with the mismatched pulley, or should I buy a newer (or used but nicer) derailleur? Photo attached of the original pulley (which I found later lying in the street) and the new one from the bike shop.
https://cimg3.ibsrv.net/gimg/bikefor...850dd32315.jpg
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The bike suddenly started shifting poorly - wouldn't go into the smallest cog - and adjusting the cable tension on the fly with the barrel adjuster at the shifter didn't help. It didn't occur to me to check the derailleur itself (and I was running late, didn't want to stop). I noticed this derailleur has both pulley bolts on the same side which I suspect explains the problem, the upper one spins in the direction that would tend to loosen the bolt. All my other bikes have the upper pulley bolt with the head on the opposite side from the lower one.

70sSanO 11-06-21 08:00 PM

It all depends on whether the STX was running narrow pulleys. 6/7 speed pulleys were wider. When 8 speed came out 10 tooth narrow pulleys were used. Yours looks like a narrow. If you use a wider pulley the attach bolt will be too short.

8 speed narrow 10t pulleys are almost impossible to find. Unless you are running at the max cog or above, you can probably use a set for 9 speed.

John

nathand 11-06-21 09:04 PM


Originally Posted by 70sSanO (Post 22298670)
It all depends on whether the STX was running narrow pulleys. 6/7 speed pulleys were wider.

It's a 7 speed. The shop that sold me the replacement pulleys also gave me a bolt off a spare derailleur but it's too short.

70sSanO 11-06-21 09:54 PM


Originally Posted by nathand (Post 22298720)
It's a 7 speed. The shop that sold me the replacement pulleys also gave me a bolt off a spare derailleur but it's too short.

If you can find the rear derailleur part number. If it is an MC-34 it is 7 speed. If it is MC-38 it is an 8 speed rear derailleur. It really doesn’t matter if the cassette is 7 speed, an derailleur spec’d for 8 speed will work fine.

Not sure what bolt they gave you.

John

Edit Added: Just compare the thickness of the new pulley to the lower pulley.

dsbrantjr 11-07-21 10:19 AM

If you decide on a replacement, Shimano (or compatible) 6- through 9-speed and 10-speed road derailleurs all have compatible cable pull ratios.

ThermionicScott 11-08-21 09:51 AM

I've got that same set of replacement pulleys in my spares box, but haven't tried to use it yet. Both pulleys are identical as far as I can tell, so either one could function as a guide or tension pulley, I guess.

As for the bolt, you might have to buy a donor RD from the same time period, or just buy another 7-speed compatible RD. There are lots out there that would work. :thumb:

nathand 11-08-21 11:05 AM


Originally Posted by ThermionicScott (Post 22300017)
As for the bolt, you might have to buy a donor RD from the same time period, or just buy another 7-speed compatible RD. There are lots out there that would work. :thumb:

If I buy a replacement RD, recommendations on whether I should buy the same model (seems there are plenty of used ones on eBay, roughly $25), or upgrade to a used Deore (more like $40 on eBay), or get a more modern low-end 7-speed such as Tourney?

ThermionicScott 11-08-21 11:50 AM


Originally Posted by nathand (Post 22300114)
If I buy a replacement RD, recommendations on whether I should buy the same model (seems there are plenty of used ones on eBay, roughly $25), or upgrade to a used Deore (more like $40 on eBay), or get a more modern low-end 7-speed such as Tourney?

If you can find a NOS/NIB/low miles STX-RC, it would be fun to keep it original-spec. My only concern with buying a used RD is worn pivots.

nathand 11-08-21 12:26 PM


Originally Posted by ThermionicScott (Post 22300170)
If you can find a NOS/NIB/low miles STX-RC, it would be fun to keep it original-spec.

For what it's worth, this is an "STX" (no "-RC"). Any idea what the difference is?
It's the original derailleur on a 1996 Trek 930.

ThermionicScott 11-08-21 01:03 PM


Originally Posted by nathand (Post 22300233)
For what it's worth, this is an "STX" (no "-RC"). Any idea what the difference is?
It's the original derailleur on a 1996 Trek 930.

Oh! My brain did an auto-complete on me... I think STX-RC was just the next generation of STX. Could be wrong.

nathand 11-17-21 02:46 PM

I stopped by my local bike co-op yesterday. They have a small drawer full of derailleur pulleys and related parts, and I found a bolt that fits although it's clearly not the "right" one. There's maybe a little less side-to-side play in the replacement pulley than with the original guide pulley but the shifting works (a little noisy between the smallest two cogs) so I think I'm set for now.


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