Jicafold

So I have this Shimano deer head rear derailleur. It doesn't have a barrel adjuster to adjust the trim. I looked online at other photos and the ones I saw had a barrel adjuster threaded in. However, mine doesn't even have any threads. Is the cable supposed to go directly into it and rely on the adjuster at the shifter end instead?

FBinNY 

Yes, that derailleur is intended to be used with flat bar levers that have adjusters, so there was no reason to have them on then RD. The cable goes to the fitting but will need a ferrule.

Jicafold

Excellent. Thank you for that!

Andrew R Stewart 

Actually any friction shift lever will trim this der, not only flat bar ones. One could also add a cable tension adjuster to the system. Like an in line style placed along the cable casing at some spot. Andy.

dsbrantjr

Or if you have downtube cable stops you can replace them with stops which incorporate adjusters, like these: https://www.amazon.com/CABLE-STOP-OR8.../dp/B007HOHVBI

Jicafold

Excellent. All great ideas. It is going to be used on a Specialized mountain bike though with new grip shifters and yes, they have adjusters.

Jeff Wills

That derailleur was made before index shifting, and thus might not work well with Grip Shifts. You would be better off installing a newer index-compatible rear derailleur and selling the "Deer Head" derailleur on the Classic & Vintage For Sale subforum.

(Assuming you are using the Shimano-compatible Grip Shifts. If you have the SRAM-compatible Grip Shifts, only SRAM derailleurs will work. )

Homebrew01

Yes, it would be dumb-luck if it works.
"friction" derailleurs don't need an adjuster. You just set the limit screws and ride.

Jicafold

I did notice that when I reistalled it. I substituted an indexed derailleur, Sora long cage, it it worked great. So why is that? If the indexing works at the shifter end why does the rear derailleur matter as long as I am not mixing Suntour and Shimano?

70sSanO

Without getting into the slant parallelogram design geometry of pre-index to post index, the basic reason is that the rear derailleur moves a certain amount as the shift cable is pulled. Prior to indexing there was no need to design a derailleur that moved a precise amount between the first and 5/6 cogs. With friction you just moved the lever what was needed to make a good shift. Index derailleurs have a specific throw ratio that moves the derailleur a specific amount for the amount of cable pulled. There are those who can give you a lot better information.

If you really want an interesting history lesson research Suntour and Shimano's Centeron pulley.

John

Jicafold

I figued the term "slant paralellogram" was going to be used, however, I figured, erroneously, that the new and old style derailleurs from Shimano still all followed the same arc of motion. Therefore, one with indexing would just have specific stops along the way and the other being infinetly adjustable. I could be more specific in my thinking however that would require a marker, a large tablet of paper, and an easel.

Jeff Wills

One of the neat things that Shimano has done is that their cable-pull-to-derailleur-movement ratio has been the same for most of their rear derailleurs since they introduced "SIS" indexing. I once combined a derailleur from the '00's, a shifter from the '90's, and a hub from the '80's and it all worked fine. Campy has had several "standards", and SRAM is out off on its own.

You can use almost any index-compatible rear derailleur made in the last 30 years on that bike. (Even non-Shimano.) Pre-indexing, though, all bets are off. It could work, but that's a whole 'nother kettle of monkeys.