M923A2 horrible loud noise coming from the differential or transfer case - 5-Ton

[madcroc1]

Well after I changed the Gear Oil in the transfer case (and all my axles) I have not been able to get the horrible noise to come back yet. After seeing the shavings come out of the old gear oil, I am still a bit worried but the truck is running and riding excellent. I'm still in the market for a used transfer case just as a backup. I know some of you got me some pictures of ones you have for sale. Let me know if any of those are still available...

I also noticed that while the TM states that the truck needs to be in N neutral to shift into low, I didn't see anywhere that it states that the vehicle should be moving to shift it in. After lots different attempts, I figured out that I can only get the truck to shift into LOW when the vehicle is both in Neutral and when the vehicle is moving (5 mph or more).

 

[Suprman]

Mine is tricky to get it to go between high and low both ways I have to be in N with a roll or move a little then try and move a little more and eventually the gears line up and it goes right in.

 

[madcroc1]

I have learned, YES it needs to be in neutral like the TM says no matter what, but I have learned that if I move a bit faster like 15MPH and shift into N it will go in better as the vehicle coasts (its sincs in around 10 mph)... I was never able to get it in while standing still in N nor while moving too slow ....

Let me know what you find out..

 

[wsmayeux]

Just an idea..... I have had an m35 and a m923. Both trucks exhibited similar conditions from time to time. What i found was that the driveline brake shoes would vibrate in the drum making an awful noise. It was caused by a little metal spring that holds the shoes in position. The metal fatigues and does not hold the shoes in place. On the m35 this was easily diagnosed by slightly applying the parking break when i heard the noise. I was able to feel the chattering in the handle, and the noise stopped. However, I dont believe you could do this in a 939 series because of the intergrated spring brake application. Perhapse if you applied the emergency brake overide, but im not sure it would be safe to do so while driving at those speeds? Any input?

 

[KaiserM109]

A wild shot, but maybe you were hearing the same thing I was when I drove my M923A1 from Ft. Benning, GA to Ft. Worth, TX. The noise would start in at about 45, or 50 MPH and slack off at 55. It was definitely coming from behind me and sounded like something was ripping itself apart. I pulled off to the side of the road several times, but I could never find anything.

Long story short, it turned out to be my spare tire bracket. I tied a tie-down strap around it and enjoyed the rest of the ride.