fujifinest

So I bought a 1991 lugged Trek 750 black/white/yellow. After cleaning it up and setting the derailleurs, I had this problem in the small cog where it kept skipping. The bike had replacement Shimano brake shifters model ST-EF65-7R/L with Suntour XCE rear and Suntour front derailleur. I used the Park youtube video to refresh my memory, but in the end I still had the problem. I brought it to my local mechanic and he said the Shimano and Suntour indexing were not compatible. He made some adjustments and it seemed to work reasonable. Today I did the complete wax job in preparation of putting the bike on Craigslist (I have 2 Trek 750s, I'm keeping the 1996 Ice Blue one), then I decided to make sure the recent tune was good. Unfortunately it's exactly like when I brought it to the mechanic. Under load it skips in the small cog. Since my mechanic is off on Monday, I went ahead and took the Shimano STX front and rear derailleur off from my other Trek 750 with idea of using them to make an all Shimano compatible system. I found out the tubing on the 1996 & 1991 Trek 750s are not the same size, so the front clamp for the Shimano STX from the 1996 Trek 750 was too big. So I put the Suntour front derailleur from the 1991 back on. After several hours, I could not get it to work correctly and was wondering if the Shimano STX rear was the problem? Does anyone have some insight about what to do next? Thanks, Nelson

alcjphil

The problem could be as simple as a worn out small cog. They wear the fastest, especially if the previous owner rode much of the time on that cog