With any luck, the following may help explain your "clunking" and vibration problem.
Let me preface this by saying that I own a 78 CJ7, 304 V8, automatic transmission(Turbo 400), Quadratrac full-time 4 wheel drive, "The Golden Eagle" model. Damn, that was a mouthful, eh? Anyway, if your 79 has an automatic, it should also be the Turbo 400/Quadratrac combo unless it was a really late production 79 that bled over in the 80 production year or somebody changed it prior to you getting it.
That being said, if yours is equipped with the Quadratrac, fear not, the "clunking" and vibration you feel during tight turns at low speeds is a very common complaint and problem with this transfer case and it is called "stick-slip". I have felt it and would describe it more as a rough, vibrating, pulsating sort of chatter, maybe like driving over a dirt road that has "washboarded" out for you desert guys.
Anyway, let me ramble more....
. Because the QT was not as common in the CJs as it was in the full size Jeep models, most of the good info on this particular t-case is availabe on the full size jeep forums.....like www.ifsja.org.
Anyway, I'll just skip to the info in the article I found on their site:
"Stick-Slip Condition.....When the brake cones in the Quadra-Trac limited slip differential stick and release, it is under a torque windup condition as in a conventional transfer case. Sudden release of the cones under this condition results in a constant, pulsating, grunt-like or rasping noise. This is a low-frequency noise that is most noticeable to the driver at slow speeds, such as when slowly turning a corner, or when maneuvering to park the vehicle.
Stick-slip noise will not occur when the vehicle is driven in a straight-ahead position. If a noise similar to stick-slip, but much louder, occurs in the straight-ahead position, the chain should be inspected for excessive looseness
Proper lubricant is important in preventing stick-slip noise. Use Quadra-Trac lubricant or equivalent only. Multi-grade, detergent-type oils must not be used. A stick-slip condition caused by improper lubricants may be corrected by completely draining the Quadra-Trac and low range unit (if equipped) and refilling with the specified lubricant.
NOTE: If a vehicle is not driven for a week or more, the stick-slip condition may occur when the vehicle is first driven. This is considered normal and should be of no concern, as the noise will usually disappear with continued driving.
Uneven tire inflation pressures and mismatched tire types and sizes will also cause stick-slip noise. All tires must be inflated equally and must be of the same size and type.
The manual also goes on to say that stick-slip continues it may be corrected by checking the tire pressures, and changing the QT fluid. The manual also advises to (Quote) Drive vehicle in circles, both clockwise and counterclockwise for approximately 15 minutes to allow lubricant to circulate throughout differential NOTE: When driving the vehicle in circles do not turn the wheel to the stop position. (End quote)"
Anyway, I hope this helps and I bet it will if you do indeed have the QT transfer case. In fact, a quick way to determine if you do for sure is look in the glove box, there should be an "Emergency" t-case switch in there. If there is, you got a QT.