My current crankset is 48/38/28 and I have an opportunity to give the Shimano CSM-771 11-36T a try. I got shifters and derailleurs that I think will work work (Deore XT and long cage), but not sure of the crankset. Just curious if it will work....I realize the question is going to come up as to why I would want to, but it's more of a "I can try it because it's available to me" than a "I really gotta do this" reason. Won't cost me more than the time to install and setup, so wanted to get your thoughts on this.....figure I could probably climb a tree with it

You don't say what size cassette you are using now. If the chain was maginally long enough before it will be too short for some gear combos with the larger cassette. You might have to get a longer chain if this is the case. Otherwise it should work fine.

You don't want to find out that your chain is too short when you are out on the trail and try to shift. You can bend or break your derailleur!

You have a 10-speed shifter currently?

The "9-speed" MTB RDs are rated up to 34T, but the 36T should work fine, considering people have reported using 30T cassettes with 27T-max road RDs. You'll be right at the 45T chain wrap capacity, which is fine, but it would be best to size the chain based on the big/big + 1" method.

It's best practice to replace the chain with a new cassette. Save the old chain with the old cassette in case you have a use for it later.

Setting aside the technical questions, that 28x36 gear will be pretty much unridable, unless you have excellent balance, I would think!

First, thanks for the responses. Second, yes, I have some 10-speed shifters. Third, yes, a new chain would be in order...and lastly the 28-36 combo would be a heckuva balance challenge! I may just do it to see....so if I do this I'll let y'all know how it feels..............

It's a higher gear than a standard 22x32 low gear on my MTB. Granted, it's used on steep climbs.

22x32? I suppose if I were going up a hill that needed that gear, I'd just toss a rope up with a grappling hook on the end and climb it Batman-style...
https://www.youtube.com/watch?v=EUuv_fEJMpI

Much lower than a 16" gear is tough to get restarted on a hill , particularly if you have toe clips to flip over before the Momentum goes away..

Though, twiddling up a hill with touring gear aboard makes a sub 19" gear use full ..
it's faster than walking.