M38 Transmission / Transfer Case Noise

[KHH37435]

1st and 2nd gear in my T90 are as quiet as a modern manual transmission, but when I shift into 3rd gear there is immediately a very noticeable gear whine. The whine is not so noisy you can't carry on a conversation while driving, just much noiser than in 1st or 2nd gears. Also, the faster I go in 3rd gear, the whine gets less. I rebuilt the transfer case about a year ago, but I was wondering if the gear whine in 3rd gear is normal, or could I benefit from a rebuild of the T90?

[maeserik]

I have the same problem, not much noise but i hear it when the jeep is warm in 3de gear. The intermidiateshaft and bearings are in good condition and are showing no playing. maybe a bearing in the T90 ?
Our GPW did not have this problem.

Erik

[Beacher425]

Same here. the whine is only between 30-35 mph and only under load. I have gotten it up to about 30 in 2nd gear and it sounds like it is starting to whine as well. Could it be the rear diff? Transfer has new intermediate shaft and bearings. the rear propeller shaft has about 10 to 15 degrees rotational free play in it whereas a second M38A1 I am working on has only about 5 degrees of rotational play.

[Beacher425]

This AM I disconnected the rear propeller shaft from the transfer output and attached a spare companion flange to the parking brake drum bolts just to hold things in place. Started it up and "accellerated" in place to bring the speedometer up to 35 mph, running through all 3 forward gears. No whine. therefore I believe that the whine is from the rear diff. I will be opening it up sometime this week and will post what i find.

[Bretto]

Be advised though with that no drive line run test, you had no load on anything so you may or may not get any results. What you could do is keep the rear drive shaft off and go for a drive in 4-hi (front wheel drive) and see if you hear what you heard. This will get the rear end spinning. Although if it is the rear, you still may not hear anything doing this since the noise could be traveling up through the driveline. Which brings me to another thought. Have you checked your ujoints? How's the slip joint in the shaft?
Sometimes if the pinion bearing is bad enough, you can physically see it move slightly just by wiggling the input yoke up and down.

[wesk]

It's always best to troubleshoot driveline noise or whine under the same operating conditions you had on the road. Raise the jeep and place it on four jackstands (two under each axle outboard of pumpkin). Now with a helper in the jeep run it in both 2 and 4 WD through all gears while you listen to the running gear. The use of a stehoscope may be needed.

As mentioned above removing the actual load from the tranny / transfer will in fact allow the tranny/transfer to run much more quietly then it does loaded.

[Beacher425]

Excellant points. I will try two these two things next:

1. I raise the jeep on 4 stands and test.
2. I have previously replaced the ujoints and slip joint is well greased and seems fine. I have a spare shaft with new ujoints I can swap out and see what happens.

Any thoughts on the free rotational play of the shaft? It is just so different from the other jeep I am working with (which has its own set of chalenges).

Thanks!

[wesk]

Rotation of the shafts relative to the ring and pinion in each axle assembly can be anywhere from 5 to 90 Degrees and not be a real issue. Yes, it is indicative of collective wear issues but we seldom push ourselves to a ring and pinion rebuild until the loud clunk associated with starting the jeep in motion becomes too distracting. The rear axle always displays more play because it gets the higher wear rate due to utilization rate being higher.

[charlesfitton]

So where did this end up?

What was the problem?