yo,
If you just bought the Bronco; the clunk coold be caused by;
Clunk, Driveshaft; "...take it out, mark it, and separate it at the slip yoke. Grease the splines heavily, and put it back together, using new clamps on the rubber boot. Be sure to mark it before taking it apart, in order to line the splines up the same way. You can also drill and tap and install a zerk fitting in the outer part of the shaft..."
Source: by spdloader
& "...could be a few things.. U-joints going out on the driveshaft, slip shaft needs greasing or 3rd member is warn and loose. get under and see if there is any side to side movement with the ujoints on the shaft, there shouldnt be any side movement at all; than grease your slip-joint (search) and go from there...& by ElKabong (Ken, El Kabong); Instead of sliding into the t-case like a car driveshaft would into a trans, a Bronco driveshaft normally is two pieces that slide together. The slipshaft is normally covered by a rubber boot in the middle like in the pic below; When you check the u-joints as Spiked described, park it on a flat spot, block the wheels & put it in neutral. That way the driveshaft will be free to move if the u-joints are bad..."
by spikedzombies (O' Black Betty) & by ElKabong (Ken, El Kabong)
Borg Warner 1356 Transfer Case Clunk or Thump on Take-Off; "...Another common complaint of the 1356 is that it will sometimes exhibit a driveline thump or clunk on take off. Many shops have spent considerable time balancing drive shafts, replacing u-joints, mounts, etc. without success. The problem lies inside the transfer case itself. A careful examination of the rear output shaft will reveal excessive end play between the shaft and the rear bearing, and between the rear bearing and the extension housing. You should use shims to take up the endplay between the output shaft and the rear bearing retaining snap ring (figure 7). You can use Chrysler part #00015128 for a shim kit that will enable you to take up the endplay between the bearing and the output shaft snap ring. Figure 8 shows how to take up slack between the rear output bearing and the extension housing using Spicer shim kit 701121X which fits the outside of the bearing and prevents it from traveling rearward against the extension housing. This shim is designed for a pinion shim in a Dana 35 rear end and fits perfectly. By using these methods to fix the endplay of the output shaft you will solve many problems that have baffled dealers and other repair shops for years..." (pics are gone)
Source: by Mike W at atra.com via web.archive.org
Clunk; "... A clunking noise may be heard from the upper and lower ball joints on some vehicles. Early Wear TSB 96-23-15 for 73-96; This may be due to early wear of the joints caused by entry of water and contamination into the ball area. ACTION: Replace the ball joints with a new integral seal design ball joint. Refer to the following Application Chart for correct part usage. The new ball joint should reduce the possibility of moisture and contamination into the ball joint. Refer to the appropriate Service Manual for removal and installation procedure..." Source: by Ford via Chilton