Transfer case, drive lines and differential- troubleshooting

ChevyDude123 · July 16, 2020

I’ve searched previous forums and haven’t found the feedback I’m looking for, although this is a common topic. So bear with me.

I have a 1999 Silverado 1500... 5.3L.... 4l60e... 4WD... NP246 TC.... 3.73 gear ratio... 160k miles. The symptoms I’m having are namely: Large clunk when shifting into reverse. A less noticeable, but still at times, a clunk when shifting into Drive. Harsh down shifts when coming to a stop from cruising speeds.

Today, I put the truck on 4 jack stands so I could get a better idea of what is going on. After being under the truck during shifts between Park Drive and Reverse , it seems to me the “clanking” is originating from the Transfer Case. And mainly from the output shaft that drives the front diff. When the truck is turned off and in park, I can manually with my hands rotate the front drive shaft back and forth and replicate the same (ish) banging noise I hear when making those shifts between P D and R. The noise is consistent whether the truck is in 2WD, 4 HI, or 4LO.

I guess my question in general is what testing can I do to further look into this and figure out the root cause? Would these symptoms typically originate from the tcase?

My long term plan is hopefully to replace both the Transfer case and front diff with either low mile junk yard OR remanufactured units.

after replacing those things, assuming a good install, do you believe the “clanking” will be fixed? In general, the truck is shifting through gears like dog ******. But I love her and want to renew it over time.

02z71thundercat · August 19, 2020

I am having similar issues with my case. I gave almost the exact same set up, except 4.10 gears and 2002. Changed the fluid and it looked very dark and FULL of shavings. I'm going to crack it open soon and assess the damage but i assume the problem is the common pump rub starting to occur. Next step is the merchant automotive pump-rub kit which is probably cheaper than a whole transfer case. Give it a try!

davester · August 19, 2020

The clunking doesn't go with the pump rub problem, other than all the oil leaving the TC via the pump rub hole and the internal bits slowly turning to mush. But I don't know what your clunk is...

Where does the banging noise come from, the TC or the front diff. Maybe using a mechanics stethoscope to narrow down where the sound comes from.

If you do get a junkyard TC, I would suggest getting bearing/seal kit, output shaft bushing (don't know why it's sold separately), and a pressed metal plate for the pump rub issue, and install them, then swap the TC's for minimal downtime.