Bicycle Mechanics - Replacing drivetrain on a 1990 Diamondback Ascent

All,

I am looking for your advice on replacing my drivetrain.

I have a 1990 Diamondback that I use as my daily commuter. It is outfitted with the original Shimano Exage 400 group. It is a 7-speed RD. The freehub is Shimano HyperGlide system. The shifters are integrated brake levers/index shift levers. The crank is of the Biopace type
Lately I have been having trouble with the rear derailleur. I adjust it about every 200 miles, but within a few days the chain starts to make noise, skip a cog, refuses to shift at al, or shifts on it's own.
When i brought it in for service earlier this year, the mechanic at the LBS mentioned that the rear index shifter was about worn out and may have to be replaced in the near future.
The FD and crank seem to be in good shape

So the time has come to take some action. I have a few scenarios that i can think of:

1. Replacing index shifters and housing.
I was thinking of the levers and cables/housing to start with. Does Shimano still make index shifters that work with a 7-speed? Do you think that this will solve the issues described above?

2. Replacing the rear derailleur
Does Shimano still make 7 speed derailleurs? When I look at their websit it is all 8-speed and up. Should ei replace the shifters as well in this case?

3. Changing the rear derailleur to an 8-speed.
Would it be worth and possible to change the rear derailleur to an 8-speed. I do understand that I need a new cassette and chain in that case as well, in addition to changing the shift levers and cable/housing. Could I still keep my Biopace crank?

Could you comment on which of these scenarios make sense from a material and cost standpoint?

Sorry about the length of this post. I appreciate any advice
Duppie

I would look into #1. You may have a hard time finding 7-speeders, though. You can always go with 8-speeders. The spacing is very close and it will often work OK (I have a friend that uses 8-speed shifters on a 7-speed cassette). If it doesn't work well, you can just replace all the spacers in your 7-speed cassette with 8-speed spacers (with perhaps a 1mm spacer behind it all to make sure the lock-ring locks it all down).

If the rear derailer is still working well, no need to replace it. But if you do, you don't need to find a "7-speed" as all Shimano compatible will work. Note that SRAM has some 1:1 rear derailers that don't work with Shimano 2:1 pull ratio. Shimano also has some low-normal as well as the standard high-normal (which is what you have) rear derailers. They both will work fine with Shimano shifters, though.

You can't put an 8-speed cassette on your freehub. It's too wide to fit.

Hey,

the ubiquitous Sora shifter is available in 7 speed. Other than cogsets and shifters, almost no other Shimano parts are speed dependent. That is to say, you could use a "9 speed" derailleur with a 7 speed cassette and shifter with a "6 speed" chain on "8 speed chainrings". 9/10 speed chains are different though.

I'd recommend getting a new shifter set. STI's don't last forever, and 10+ years is a good innings. I'd probably also be resigned to a new rear mech, chain and cassette and some point.

Hey,

the ubiquitous Sora shifter is available in 7 speed. Other than cogsets and shifters, almost no other Shimano parts are speed dependent. That is to say, you could use a "9 speed" derailleur with a 7 speed cassette and shifter with a "6 speed" chain on "8 speed chainrings". 9/10 speed chains are different though.

I'd recommend getting a new shifter set. STI's don't last forever, and 10+ years is a good innings. I'd probably also be resigned to a new rear mech, chain and cassette and some point.

He's not talking about a bike with STI. Most likely grip, click/trigger shifters.