In my 1986 Dodge Ramcharger the transmission No reverse

Sorry we do not have parts.

The controls for the a/c vents are vacuum controlled. Check for vac leaks on the engine.

should be dana 44's.... the is a front axle disconnect on the tube operated by vacuum ...when shifted to 4wd, the slide engages the 2 axles to make one

I believe the capacity is 35 gallons

Either the u-joints are bad and that is what is clunking or the tranny fluid and filter need to be changed. usually it is the u-joints that clunk

Probably the solenoid. A thread search at Ramchargercentral.com will give you all of the details on how to diagnose and repair them.

Sounds to Me Like There is a "U" Joint Problem Here. Although normally it would "Clunk" upon Engaging Forward or Reverse, I would RULE OUT This FIRST, Then move on to Motor Mounts, Transmission Mount, Then DIFFERENTUAL= Pinion Bearing ETC.
PLEASE DO NOT Count me OUT, as I am Available to Answer Questions as you go along with your Inspection, ALONG with MANY MANY Other GURU's At FixYa.com . Good Luck With Your Search & Hope you find its's a Small Problem.

had same problem it was fuseable links by battery old and brittle

Sounds like it's time to replace the U-joints

under the wheel