Replace '86 Trek Deraileur??
 

I'm rebuilding my wife's trashed 1986 Trek 400D Elance road bike (6 speed freewheel, Double crank, 126mm rear axle). The main assembly body of the Shimano L-525SS rear derailleur is snapped in half so I am looking for a replacement derailleur that will work with the Shimano S-242 SIS shifters. will any SIS compatable derailleur work or do I need to find a 6 speed model in order for it to index correctly?

Best Regards,

Marcel

With a 6-speed indexed shifting Shimano drivetrain, you can use basically any shimano rear derailer made since the advent of indexed shifting (excepting 7- and 8-speed Dura-Ace) and it will have the same cable-pull ratio.

You wouldn't want to use a derailer that came with 6-speed drivetrain, on a bike with 10-speed stuff, bceause the 6-speed-era derailer will be more sloppy, less precise.
But a 10-speed-era rear derailer would work fine on your system. Find a cheap 6- 7- or 8-speed Shimano rear derailer on eBay is my recommendation.

Shimano RDs aren't picky, as a rule. There might be an issue with chain width if you were to go for a 9-10 spd one, but a lower-end 7-spd should do fine. Don't worry abt the indexing, that's all done by the shifter.

The derailer does play a role in indexing, because it has to move the correct amount per increment of cable pulled by the shifter. This is the same for all Shimano rear derailers since the advent of indexing, except 7- and 8-speed Dura-Ace. The good part is that the odds of coming across an old Dura-Ace rear derailer are very low.

Good point about 6-speed chain possibly being too wide for a 9- or 10-speed rear derailer cage.
If this did happen, an 8-speed chain would work and shift fine on the 6-speed drivetrain though.

If you'd like a brand new Ultegra rear-derailleur, but don't want to spend $80 - $100, try this:

http://www.cambriabike.com/shopexd.a...EAR+DERAILLEUR

It's for real - these are excellent units - smooth and positive shifting in any sort of drivetrain. Just about.

+1 On the Cambria deal, I picked one up myself a couple of weeks ago. I can't believe that deal is still available!

I have one in reserve and two in service. I'm thinking I'll get second in reserve. I finally found a NOS Huret Eco-Duopar (original run) on eBay. Up to my ears in derailleurs - but I don't mind! :D

Thanks for all the advice! That is a great deal on the Ultegra rear derailleur and Cambria but their website says the max rear cog is 27T and my freewheel is 28T. Is it possible that the derailleur will work with my freewheel?

FWIW I'll be using a SRAM PC870 6-7-8 speed chain.

Do NOT be concerned. Shimano always low-balls their MAX T for all their derailleurs. The Ultegra will work just fine with 30T (and 28T) cassettes - and many people claim they're fine & dandy with their 32T cassettes and/or freewheels.

Order away!