M917 Drivetrain noise

[crownfire]

My M917 recently developed a noise like a knock or thump that is speed sensitive and only occurs during acceleration. Its also not noticeable until I get to 30 MPH. Any ideas on what it might be? My first thought is a U joint.

 

[Construction]

Where is the knock coming from? Front, rear, under your seat - where do you feel it? Does it happen when you accelerate, decelerate, with a load, no load?

 

[crownfire]

It definitely sounds like its coming from the rear end but only during acceleration. It sounds the same with a loaded salt spreader as it does empty. If it was doing it all the time I might think it was a tire separating based on the sound. Could a missing tooth on a ring gear make a similar sound. Hate to start taking things apart to find it but I also don't want to cause additional damage by driving it more. Thanks for the help.

 

[Construction]

Check the fluid levels in the axles first, look at the drive shafts, check for play in the u joints and the pinion bearings, lift the wheels individually and check for "play" in the wheel bearings, etc. Exhaust all possibilities before opening up and pulling things apart.

If all seems OK, then take the differential covers off and take a look. It would be odd that the knock is speed specific.

Does the truck shake/vibrate too on acceleration?

 

[crownfire]

The truck shakes alot anyway but it seems that it may have a vibration that correlates to the noise. I had been driving quite a few hours plowing snow and just noticed the noise on the way back to my shop after finishing up. I was pretty tired and just wanted to park it. Up to that point the truck had ran over 24 hrs non-stop without any trouble other than the shutter- stat not wanting to work like it should occasionally. I'll check all that you mentioned and drive it a little more.

 

[crownfire]

I got the truck jacked up yesterday and the noise is definitely coming from the front rear differential. It start at about 25 mph and continues as long as the accelerator is pushed. It immediately stops when the truck coasts. It is no different on the road than with the truck jacked up. It sounds like its coming from the front side of the differential near the input shaft. I took the shift actuator off to take a peak and everything looked fine while i turned the wheels by hand. Plenty of oil and it doesn't smell burnt and no signs of water. I hate to tear this whole thing apart of it could be something simple. Are their any common failures in this set up?

 

[crownfire]

Putting it under load doesn't change the noise either. I just pulled a 25,000 track loader with it and had the same noise at 25 MPH and up but it didn't sound any worse.

 

[Construction]

Could be your pinion bearing, although that should sound worse under load. I would start with changing the fluid with a synthetic like Amsoil.