Bacciagalupe

So, I have this half-way decent 80s road bike (REI Novara Strada), steel frame, fit is good, wheels seem to be fine. I've been slowly replacing and repairing parts here and there: bottom bracket, chainrings, brakes.

Next thing to upgrade is the rear derailleur; it works, but rattles a bit, seems a little worn, and I just don't trust it for century and fast rides. It's a Shimano Light Action RD; bike has a 52/39 up front and 13-28 7-speed freewheel in the back, upgraded from 6 speeds. Using new 7-speed downtube shifters.

Any (specific) suggestions on a compatible replacement? I assume a new Tiagra RD will be fine, just want to be sure.

Little Darwin

Any indexing Shimano RD except for early Dura-Ace, either road or mountain should be fine as far as compatability, as long as it can handle a 28 tooth rear cog. And most should be able to do that.

This assumes the 7 speed down-tube shifters are Shimano/compatible and not Dura-Ace. If so, you need an early Dura-Ace RD.

jsmithepa

Upgrade to Index Shifting and u'd think u've gone to heaven. Unfortunately, u may need a new rear wheel with the correct gear cluster. Tons of used 7-speed stuff out there am sure.

Bacciagalupe

Indexing works with the current setup, but is really touchy. I had it working fine for awhile, took the bike into the shop for a quick check, mechanic tweaked the RD and voila, indexing is out. Go figure....

Is there a way to determine if the existing RD is short or mid-cage?

jsmithepa

It's very simple.

Shift to big chainring/big cog. If cage looks like it can go no further, it's short.