97 Discovery Transfer Case Noise

[Tim Wilson]

My 97 Disco transfer case has started making a whirring, grinding noise. I'm pretty sure it's the transfer box vs transmission because the problem started shortly after a gear box overtemp light, and the "tone" of the noise changes depending on the setting of the transfer case shift lever. I checked fluid levels of both the case and transmission and they're good. Any suggestions on what to do, or where to look first? I know the rear main bearing and seal can be changed without dropping the transfer case ... front too, most likely. Are these common failure points and likely sources of trouble, or should I just bite the bullet and replace the entire transfer case?

 

[Disco Mike]

How often do you change the gear oil, what weight do you use? I would suggest that you drain your oil while looking for metal chunks, bearing surface or anything other then what normal gathers on the magnetic plug. If not a lot there consider putting a bandade on it so to speak and fill with a 85W/140

 

[Tim Wilson]

Thanks, Mike. I haven't changed the TC oil in .... ages. I did drain and refill when this problem began and noticed nothing unusual, other than the level was low. There were some filings on the magnetic plug, but nothing of significance. I'm a little reluctant to try the heavy-weight oil approach, simply because the sudden appearance of the noise right after that high temp light implies something has changed - my best guess would be a bearing is failing - though I suppose it's possible the oil was low, got hot, and lost lubricity, thus the noise. I haven't driven it more than a block or two since changing the oil ... maybe the fresh stuff hasn't had a chance to circulate well through the gearbox?

 

[Disco Mike]

Yes, something has changed and the heavier oil will prolong it's life and since it is so costly to rebuild a t/case, run on borrowed time and keep you eye open for a good used one to install somewhere down the road, for less.

 

[Tim Wilson]

Sounds like good advice to me. I'll refill with heavier-weight stuff and drive it a bit ... certainly can't hurt at this point. I'm officially in the market for a 97 Disco LT230T transfer case, if anyone out there has a working one they're willing to part with.

 

[Disco Mike]

Where are you located, this will make a difference based on high freight charges?
Be very careful when buying one, you want a warranty and need to make sure it is out of a late model 96 or newer.

 

[Tim Wilson]

I'm in Virginia ... will probably go with a rebuilt unit from RoversNorth or Roverland if it comes to that.

More troubleshooting: I drained the transfer case and took off the large access plate. Pic attached for the curious. Nothing of significance to note there, at least nothing I could see. Reinstalled the plate and refilled with 85/140 gear lube ... no change in the noise though. It seems to be noisiest in low with the CDL engaged, a little quieter (emphasis on "little") in high with the CDL dis-engaged. No problem shifting gears or engaging the diff lock, btw ... everything there works smoothly.

I put the front wheels up on jackstands, dropped the rear drive shaft, and removed the emergency brake drum. There's no oil leakage and no significant play in either of the driveshafts. With the transmission in neutral and gear box in high, CDL dis-engaged, I can hear a little noise when rotating the rear output flange by hand. I'm not experienced enough with these to know if that's normal or not, though my guess would be "not." I'll try the same check with the front driveshaft down also. Dumb question first: with the transfer case in neutral are the intermediate gears disengaged? If I can isolate the noise to the front or rear main bearings by disengaging everything else in the drive train, I might be able to get away with replacing them in place vs pulling the whole transfer case.

Thoughts, anyone?

 

[Disco Mike]

Is that fluid blue, if so what are you running in it?

 

[Tim Wilson]

That's Castrol 80/90, contaminated with the residual black stuff that was left when I drained and refilled the transfer case.

 

[actionmeter]

re: transmission transfer case

have you rebuilt your front driveshaft with greasable u joints?

Just by a rebuilt transfer case off of ebay and call it a day