Meowriano

Hi, im just curious if anyone knows if the shimano deerhead has enough range to shift a 9spd 12-36 cassette?

Ghrumpy

Not likely. It's probably not an issue of the in-out range, it's mostly the maximum cog capacity. XT Deerhead RDs have a factory max rear cog rating of 34 teeth, which is close enough probably to fudge. But that rating is only when used with the Shimano SFR dropout, which has a hanger length of 29mm, 5mm longer than the "standard" hanger. If your hanger length is less than 29mm, it's risky. Measure that first. If it's much less than 29mm, I wouldn't even try it.

If your hanger is 29mm or more, it still also matters what chainrings you have. The Deerhead was intended for use with a triple chainring, and as such can handle a 22t chainring difference and a 40t total capacity. If your chainring set has a 16t difference, you're at max capacity anyway, so I wouldn't try it then either.

If your hanger is 29mm or longer, and you have a double chainring set that is less than a 16t difference, then you will have a little spare capacity. In that case, you could run the chain a link short, which might give you the cage swing and jockey wheel gap you need to get on the 36t. You'd have to be very careful not to cross-chain big to big, but you shouldn't ever do that anyway, right? Right?

Bike Gremlin

If RD chain wrap capacity is not sufficient, wouldn't it be safer to go with the optimal chain length and just avoid small-small combo? Cutting the chain too short can cause problems in the big-big combo, like you've said. But running it at optimal length, even while exceeding the RD's chain wrap capacity, can only cause nuisance when (accidentally?) shifting to small-small combo.

Eggman84

You really need to be more specific about which Shimano MTB rear derailleur your considering using. For instance the Shimano XT, RD-M771 (SGS long cage) is designed for Min/Max Cogs of 11T/34T, a total capacity of 45T, and a max Chainring Difference of 22T. I have this RD on two different touring bikes, shifting an 11-34T 9 speed cog, and the b-screw is not turned in all the way on wither bike; not saying though that it would work for a 36T large cog. Don't see why you can't try it with a Wolf Tooth Tanpan to get to shift a large rear cog like 36T.

Ghrumpy

The reason to run the chain short is to allow the pulley cage to rotate CCW more for a given chainring, which brings the upper jockey wheel downward, increasing the gap between it and the cogs. This lets you "cheat" the max rear cog rating, but yes, at the expense of making the big-big combo more dangerous.

Ghrumpy

He was specific. There are only two "Deerhead" derailleurs, RD-M700 and RD-M700SP. 1980s stuff. The SP "Superplate" version is pretty rare IME, it has a Duopar- or Mountech-type dual-pivot cage that allows a bit more total gear capacity. Both have a max rear cog of 34. Neither have a B-tension screw, as they predate SIS.

Bike Gremlin

Thanks for the clarification. I had managed to "cheat" the max cog specs even with a properly sized chain - but there is a limit, of course.

Eggman84

Based on this website VeloBase.com - Component: Shimano RD-M700, Deore XT, the original deerhead RD-M700 (not the SP or version 2) can handle a 36 T large cog.

Ghrumpy

FWIW I am referencing the original Shimano spec sheet, and Sutherland's Handbook. Not sure where Velobase gets their information, but it does not agree with either of my sources.

bradtx

Trial and error. While generally small, the differences in RD placement and drop out width can add up to success or failure. The lack of a B screw does not help. Problems will show up as lack of lateral travel and/or inability to cope with the 36T cog. Good luck,
Brad