Possible broken output shaft retaining snap ring in the transfer case. If so, it's causing the t-case to shift in 4wd, which will destroy the synchro assembly eventually. Been there, done that, got to rebuild my t-case in the process. The sound is similar to missing a shift in a manual tranny, or more like a handful of loose change rattling in an empty beer can if you like. Known problem and weakness w/the early NV241 t-cases. Out of curiosity, did it first start the problem after getting on the throttle pretty hard, or towing/hauling heavy load?<br><br>Could be several other things too; diff bearings, u-joints etc - though most of those usually make more noise coasting than under load in my experience. <br>Just my .02...<br>Good luck,<br>-Scott

 

Oops, just noticed this was your buddy's truck. Is it 4wd? (yours listed in the sig, 4wd?)

If it is 4wd, easy to find out if it's the snap ring. Pull driveshaft/yoke out. Push in/pull out on tailshaft. It should not move (small play normal, but not much). If the shaft slides forward a half inch or more, one or more snap rings is gone. They keep the shaft from sliding fore/aft, which will cause the 4-hi synchro stop ring to grind into the sleeve. It sounds just like a manual tranny grinding gears because it is essentially the same thing. Mine kept breaking snaprings, which seemed odd. Dealer mech told me it wasn't common - but mine was the 3rd truck in the shop. Said it was &quot;a bad batch of snaprings&quot;. Turned out to be more like a design flaw. The problem seemed confined almost totally to the diesel &amp; V10's, usually regular cab (not ext.), and mostly 3.54 gears. If it is the rear snapring, you can repair w/o dropping t-case (just pull ext housing), but may require a new ext housing if the bushing is damaged (mine was, &amp; yoke ruined).

If not the t-case, it may be (as Allen T said) the tranny planetary set. Seem to recall the first few 47R trans had oil supply failures to the planetary set. Sorry can't help you there, as I have a manual tranny.

The 4wd trucks seem to be more prone to driveline problems due to the steep driveshaft angle (truck sits higher than 2wd). Axle wrap under accel. tends to work the tailshaft bushing oblong, allowing unwanted force on the tailshaft (snapring). May notice a slight howl under load (speed sensitive), or a leak around tailshaft seal (yoke area) before failure, but not always.

Good luck,
-Scott

 

Wilson,
Glad it was a simple snap ring. The V10 &amp; Diesels were bad for this for a few years. The rear springs sit up on tall spacer blocks to gain more ground clearance. This puts the driveshaft at a bad angle at the back of the t-case. The leaf springs are weaker than they were on 1rst gen trucks, so allow too much axle wrap under acceleration/braking. This tends to pull the tailshaft down, which puts the snapring under a bind. The rear bearing in the 241 t-case is way up inside, so allows the shaft to flop around too much. Eventually the tailshaft bushing will wear oval shaped (won't support the yoke enough). This will cause constant broken snap rings and seal failure at the yoke (leaking from back of t-case is often not the seal's fault - it's the bushing worn out). I had so many broken snap rings, I finally bought a kit from JB Conversions that does away with the slip yoke and goes back to a fixed yoke, with spine-stub driveshaft (like the np205 &amp; 1rst gen Rams had). Over 100K mi on it so far, no problems.

Tell your buddy to keep an eye on the yoke area for leaks. Also, first sign of excess bushing wear is a very distinct roaring sound under coasting conditions, at highway speed. Mine did it at 68 mph, when lifting throttle. Under load, no sound. BTW - make sure you remove ALL the snap ring pieces. If a small piece of it manages to work into the sump, you'll be rebuilding the t-case. First couple times mine broke, dealers repaired. They didn't get all the metal out (or totally drain the oil), so ended up w/metal frags getting into the pump and yoke. Picture of my ruined yoke attached.

Glad to help. Good luck!
-Scott

 

Thanks Wilson for posting this , this is the same problem I am having while hauling big loads when I shift and at low RPMs I get this sound. I am going to look at mine Sunday and see if that snap ring broke.<br>Ricki<br><br>