Bicycle Mechanics - Issues with Indexed 7-Speed Downtube Shifter

I've got an 80s road bike with DT shifters. Most of the components were kind of entry-level (e.g. Shimano Light Action derailleur, Biopace chainrings etc).

I've done a few upgrades, including:
- new (round) chainrings
- upgraded from 6 speed freewheel to 7 speed freewheel
- new chain (of course)
- new 7-speed indexed downtube shifters
- new shifter cables

The indexing worked for about a week, and then started going off. In theory the LBS tweaked it, but it seemed pretty much the same. It may be my imagination, but it seems like if you get it mostly right for the small ring, it will be off for the big ring.

I'm also considering an upgrade to either STI or bar-end shifters. But if the DT shifters can't keep the indexing, I'd imagine any other shifting mechanism will also rapidly lose the indexing.

Any thoughts on possible solutions?

Your cables might still be stretching, which is common. You'll need to adjust the FD and RD until the cables stop stretching. Check your RD limit screws and make sure there set correctly. Having the high or low limits incorrectly adjusted can cause shift problems as well. It's also possible your RD is worn out. If the prior owners never put a few drops of oil on the moving parts of the RD this will eventually cause it to get sloppy causing alignment problems so it cant index correctly with each cog.

OK, so the best method will be to ride using friction mode for awhile, then re-adjust the derailleurs. Any idea how long (in miles, I guess) that usually takes? I'm sure I've put at least 200 miles on the bike since I put the new DT shifters on, maybe 50 since the last visit to the LBS.

What exactly is it doing when you say the shifting is "off?" You mention there's a difference depending on which chainring you're using at the time, but be more specific about what's actually happening.

Also, what model shifters, derailleur, and seven speed freewheel do you have?

"Shifting is off" means that when in indexed mode, the rear derailleur is not quite shifting to the proper spot. E.g., I shift from the 3rd to the 4th rear ring, and the drive train starts to make that "dude you haven't shifted into the right spot" kinda noise. No problems in friction mode though.

Shifters are new 7-speed Shimano DT.
RD is Shimano Light Action. Bike was originally 6 speeds.
Freewheel is new, 13-28. No idea of the make.

"Shifting is off" means that when in indexed mode, the rear derailleur is not quite shifting to the proper spot. E.g., I shift from the 3rd to the 4th rear ring, and the drive train starts to make that "dude you haven't shifted into the right spot" kinda noise. No problems in friction mode though.

Shifters are new 7-speed Shimano DT.
RD is Shimano Light Action. Bike was originally 6 speeds.
Freewheel is new, 13-28. No idea of the make.

Since the bike is from the '80's and it was originally a six speed (friction shifters originally?), it might be a good idea to check the upper pulley on the derailleur and make sure it has a bit of side to side play in it. If it does, it should work okay with indexed shifting. If it doesn't, it's not really index compatible. The side to side play in the upper (guide) pulley is one of the things Shimano did to get ahead of Suntour in the race for indexed shifting that actually worked well.

Beyond that, it sounds like a simple cable adjustment issue. Hopefully, there's a barrel adjuster where the cable housing goes into the derailleur. If it seems the chain is trying to go towards a higher gear (smaller cog) when it's not supposed to, therefore creating the noisiness you mention, you should turn the barrel adjuster counterclockwise (loosening it). This will have the effect of increasing the cable tension. You shouldn't have to turn it much to tweak the shifting, turn it maybe a quarter turn at a time and then re-check it. If the chain seems to be moving towards a larger cog (lower gear) when it's not supposed to, do the opposite with the barrel adjuster, turn it clockwise (tightening it), and this will have the effect of decreasing the cable tension. Again, adjust in small increments and then re-check it.

Since you say it has worked properly for at least a time, I'm guessing it's just the cable tension that needs adjusting. There are, however, some seven speed freewheels that would not be compatible with your setup, but it seems doubtful you've got one of those, especially since it's a new freewheel.

OK, I gave the barrel adjuster a few quick turns. Shifting seems mostly good now. We'll see how long it holds. ;)

FYI -- the bike was actually indexed back when it was a 6 speed. It worked fine until I did the upgrades (which were kind of necessary, as the original gearing was too high for me).

OK, I gave the barrel adjuster a few quick turns. Shifting seems mostly good now. We'll see how long it holds. ;)

If it doesn't "hold," I'd advise getting a new, inexpensive Shimano derailleur. Any model will work, and will more than likely save you some headaches. Derailleurs do wear out-

Cables don't stretch any appreciable amount. Sometimes, housings are not seated well in the ferrules and will shorten slightly in the beginning, giving the impression that a cable has stretched.

Make sure your derailleur does not have worn pivots or a bent hanger. Your derailleur is 20 years old. Maybe it's time to retire it. Even an inexpensive derailleur is probably better than the one you have.

Cables don't stretch any appreciable amount. Sometimes, housings are not seated well in the ferrules and will shorten slightly in the beginning, giving the impression that a cable has stretched.

Make sure your derailleur does not have worn pivots or a bent hanger. Your derailleur is 20 years old. Maybe it's time to retire it. Even an inexpensive derailleur is probably better than the one you have.
Good to know.... I got the bike used, and I don't think it got 20 years of constant use. ;) I might replace it anyway though.

Is that a difficult job? Seems like I'd have to remove the chain, swap the RD, set the limit screws, adjust the tension, replace chain. I'm tolerable with bike mechanics but haven't done this before -- is it a job best left to someone with more experience?

Good to know.... I got the bike used, and I don't think it got 20 years of constant use. ;) I might replace it anyway though.

Is that a difficult job? Seems like I'd have to remove the chain, swap the RD, set the limit screws, adjust the tension, replace chain. I'm tolerable with bike mechanics but haven't done this before -- is it a job best left to someone with more experience?

You don't have to remove the chain. Take off the lower roller pulley, install the RD, and put the pulley back in with the chain in the right place.

It's not a big job. Go to Park Tool's site, they have full instructions.