Help, Loud Tranfer Case Noise

[dr.olds]

Hey all you wise ones, have a prob. today as i was driving down the highway, occasionally i will engage th transfer case in to 4wd hi. just to keep things moving to ensure it works for winter months. bot to day when i engaged it it made a loud zipper sound, (never heard it before!) but it did engage. Shifted back into 2wd. and pulled over, and engaged it again at about 2mph this time it just made a loud clunk (never heard that before either) but it to also would engage, never have been into the transfer case on one of these, not sure just whats in there, any advise would be greatly usefull, thanks, Eddie, BY THE WAY, It is an 02 2500hd duramax, 4x4 crew cab :cool: and the service 4wd light comes on from time to time.

[DmaxMaverick]

It doesn't sound too serious, yet. If it's been a while since you've engaged it, a stepper motor could be sticking/delayed. This should clear up itself after a few engagements. A worst-case would be a worn out synchro, which can happen after too many high-speed engagements. They are designed to engage at highway speed, but will eventually wear through a synchro. Frequency of service and quality of lube can help/hurt, as well. I do not recommend routine "testing" or maintenance engages at high speed. This should be done at low/walking speed.

In any case, I suggest a drain/fill with some quality synthetic ATF. It wouldn't hurt to check over the connectors and wiring while you're under there, and give them a fresh squirt of dielectric grease. Engage it a few times at lower speed before you use it on the highway.

[drcook]

You need to make sure that there is fluid in it. These t-cases used in our trucks have an engineering defect in them. the pump will wear a hole in the case and let all the fluid drain out. So if a person is having transfer case issues, this is the first place to start

Here is a link to the part to fix it (if this is the problem) there are other parts to fix it from other vendors, I just happened to know about this one

http://www.kennedydiesel.com/categoryresults3.cfm?Category=11&SubCategory=109&SubCategory2=135

here are some links to read about if this is the problem

http://www.thedieselpage.com/reviews/tcase.htm

http://www.duramaxforum.com/forum/how-tos-diy-write-ups/65604-duramax-allison-transfer-case-pump-rub-fix.html

http://www.thetruckstop.us/forum/showthread.php?17764-t-case-pump-rub-fix.

dave

[dr.olds]

Dmax thanks for the info, will drain and see if any thing falls out, bet i wont be engageing at highway speeds any more, so much for shift on the fly!!!!!!!!!!!!!!!!!!!! is a syncro. hard to change? thanks DRCOOK, will check into those web sites, have a feeling i will need them!!!! Eddie:cool: