Help me choose a derailleur
 

I want to replace the rear derailleur on my Diamond Back Ascent mountain bike. It is all friction shifting. The freewheel is a Shimano14-18, the chainwheels are Sugino 48-38-48. Suntour bar mount friction shifters. The way I figure it I need a 36T capacity. I am thinking about a Shimano 105, long cage, 10 speed rear derailleur. I found some attractive deals on EBAY :-) Will a 10 speed rear derailleur work OK ? I think as long as the derailleur has enough capacity then it doesn't matter if it is a derailleur for an indexed system ? Unless the derailleur pulley wheels are different ?
thanks,
Bob

I would get one that is rated for the number of rear cogs that you have. 5 according to your description, but that doesn't sound right for a mtn bike.

A 10 speed chain is narrower so the 105 might not work well with your width of chain.

After thinking about it, do you have a 14-28 freewheel with a 48-38-28 crankset? The specs you listed make no sense.

John

Hi John,
Well it could have had different chainwheels installed, I don't know for sure, I bought it used. I'm pretty sure everything else is original.

Here's a more complete description:
1980's Diamond Back Ascent mountain bike, CR molly frame.
Rear derailleur: Suntour Mountech, long cage
Front derailleur: Suntour Mountech
Freewheel: Shimano 14-28
Crankset: Sugino VT, 175mm
Crankset chainwheels: 48-38-28
Shifters: Suntour XC (handle bar mounted, friction shifters)

I suggest this one: https://www.amazon.com/microSHIFT-De.../dp/B0165T3AXI I have this RD on my Trek 720 converted to an ebike with a 5 speed 14-28 Sunrace freewheel https://www.amazon.com/Sunrace-Freew.../dp/B000AYB57S I am using a Sunrace friction shifter.

I also suggest you get a new freewheel and a new KMC X8.93 chain.

Many RD will not be happy with wider (lower number of speed) chains than they are intended for. I had a particularly bad experience with a 5/6/7 speed chain and a 9 speed Shimano RD.

I use KMC X8.93 chains on all my 8 speed and less cassettes & freewheels, and X9.93 on my 9 speeds.

Nigel,
I was sitting here thinking about maybe I should change the chain and freewheel too while I am at it. Your post is very timely.
I found the derailleur, chain, and freewheel on Amazon and I don't need to take out a loan on my house to get them :lol:
Thanks for the info, much appreciated !
Bob

If you use the Shimano 105 10 speed RD, make sure you can go to 36T. I think the spec says 32 or 34, though I’ve heard of people going a step bigger.

Hi Bob;

Glad to assist. I forgot to mention, if you haven't done it already, you should probably replace your cable and housing.

Friction shifting benefit is anything in a long cage MTB type , RD will work, adequately..



does not 'have' to be 'period correct' does it?

Yep, I just finished installing new shifter and brake cables and housings. I ordered the freewheel, rear derailleur, and chain you recommended.

They should be here tuesday. I am getting impatient now, have to wait for the parts. :) This is good though because I have overhauled/regreased the headset, bottom bracket, and wheel hubs. They were actually in great shape. Oh, and I put on new tires too.

I am soooooooooooo ready to finish it. :lol:


Bob