M739 RD Minimum Sprocket

[Lou Carpenter]

Doing a quick search on google I've seen plenty of threads about what the maximum sprocket a M739 rear derailleur can take. Has anyone any idea of a minimum? I was thinking of throwing on a close ratio cassette on, largest sprocket 23t. I know I can just try it and see what happens but has anyone any experience with this before I waste my money on a brand new cassette?

 

[slackboy]

11-32

11 is the minimum a hyperglide freehub will take.

https://www.retrobike.co.uk/threads...tal capacity of 38 for long and 33 for short.

 

[Lou Carpenter]

Very good, well done.

I was referring to the minimum largest sprocket the M739 could handle. For example when you look at modern Shimano specs they now give both a minimum and a maximum largest sprocket that their rear derailleurs can handle.

 

[Markybeau]

11-34 is the biggest range you're likely to find in 8 speed. Although that might be a big ask for an m739.

As already stated by @slackboy 11-32, which was as big as you were likely to get bitd, gives 21t range.

If you're thinking on putting on 12-23 or similar it should work fine.

 

[Tootyred]

I think he wants to fit a corn cob....and is worried the 11 - 23 would not run as the derailleur might not engage with the biggest cog.

I dont know for sure, but unlike modern derailleurs, on older stuff the parallelogram and pivots are far less aggressive angled as they never had to deal with a dinner plate sprocket.

My educated guess would be yes it probably would be fine. Tbh, why not run a short cage if you dont need the range...?

 

[Tootyred]

Sorry @Markybeau you answered whist i was slowly typing with one finger!

 

[Tootyred]

Im pretty sure they made m739 in short and long cage.......bit modern for me, so cant quite remember....

 

[slackboy]

Very good, well done

There's really no need for that, I answered the question as asked.

 

[Lou Carpenter]

Thanks for your help, even you Slackboy.

Yes, was worried the guide pulley would be too far away from the 23t to give good shifting. There's only so much you can slacken off the B-tension screw. Don't really want to change the rear derailleur, just thought I could put a closer ratio cassette on a spare rear wheel to give myself some options.