Grinding/Chattering Noise From Transfer Case

[ShookieJay]

2003 Tahoe LT, 5.3, 4L60E, NP246. I recently completed a roughly 1500 mile round trip from Connecticut to Tennessee, and back. On my way there, I started to hear a squealing noise coming from the front end. First thought was a wheel bearing, so I pulled over to check it out but didn't find any conclusive evidence of that. I continued on driving and the noise got worse and worse. By the time I embarked on the trip back, the noise had changed from a squealing to chattering/grinding sound. Once home, I removed the front driveshaft thinking the u-joints were shot. Drove it up and down the street without the front shaft and the noise was still there. So I put the front shaft back in, removed the rear shaft, and attempted to drive on front axle only in 4hi. Truck did not move at all and the noise got a lot worse. Finally, I removed both driveshafts from the truck and put the trans in neutral. This resulted in the same sound I had been hearing while driving, except this time obviously I wasn't moving at all. After putting both shafts back in, I can drive just fine in 2hi. No skipping or loss of power, but the sound is dreadful. At this point I'm sure the transfer case is toast, but I'm wondering if it's even worth rebuilding or if I should just buy a reman unit. Haven't checked the fluid yet but from the sounds of it, it probably went dry and chewed up the planetary gearset. What do y'all think? TIA

 

[rockola1971]

" I removed both driveshafts from the truck and put the trans in neutral. This resulted in the same sound I had been hearing while driving, except this time obviously I wasn't moving at all."

If your transmission wasnt in a gear then its output shaft was NOT turning so the input shaft of the Tcase wasnt turning. That rules out your Tcase. Your noise is coming from the transmission or engine. Your torque converter and tranny pump is always turning no matter what gear you are in or even neutral, as long as the engine is running.

Front diff ruled out since you were in neutral.

Your noise could be coming from the engine or accessory drive.

 

[tom3]

Is there a big chain in this unit? That might be the culprit. I'm thinking that with the driveshafts out the gear train would probably be turning due to internal friction? No noise in neutral with driveshafts in would point to that.

 

[rockola1971]

Is there a big chain in this unit? That might be the culprit. I'm thinking that with the driveshafts out the gear train would probably be turning due to internal friction? No noise in neutral with driveshafts in would point to that.

Incorrect. The transmission drives the input shaft of a TCase. In neutral the tranny's output shaft is NOT turning so nothing in the Tcase is turning. The NP246/246E does have a chain to drive its front output shaft but that chain isnt turning unless in 4wd or Auto 4wd is engaged and active AND the input shaft of the Tcase is being turned by the transmission's output shaft.

 

[OR VietVet]

Pay close attention to what @rockola1971 is saying. He will not steer you wrong. When I ran shops, I would have wished to had a half dozen just like him as techs.

 

[ShookieJay]

" I removed both driveshafts from the truck and put the trans in neutral. This resulted in the same sound I had been hearing while driving, except this time obviously I wasn't moving at all."

If your transmission wasnt in a gear then its output shaft was NOT turning so the input shaft of the Tcase wasnt turning. That rules out your Tcase. Your noise is coming from the transmission or engine. Your torque converter and tranny pump is always turning no matter what gear you are in or even neutral, as long as the engine is running.

Front diff ruled out since you were in neutral.

Your noise could be coming from the engine or accessory drive.

I've since descovered that I fell victim to the dreaded, and apparently well known (except by me) pump rub. Tcase ran dry and chewed itself up. It's strange to me though that the case was able to spin while in neutral (with no driveshafts installed) Though it stopped when in park. Engine reved up slightly on its own even, and speedo registered about 10mph. Maybe one of the shift bands was touching just enough to spin the output shaft without anything there to stop it??

 

[rockola1971]

I've since descovered that I fell victim to the dreaded, and apparently well known (except by me) pump rub. Tcase ran dry and chewed itself up. It's strange to me though that the case was able to spin while in neutral (with no driveshafts installed) Though it stopped when in park. Engine reved up slightly on its own even, and speedo registered about 10mph. Maybe one of the shift bands was touching just enough to spin the output shaft without anything there to stop it??

The 4L60E has only one band and it is for 2nd and 4th(OD) gear. I have seen trucks off the ground on a lift in neutral and wheels turning very slowly but not in park. Something aint right at all there! Nothing should be turning the Tcase input shaft with the transmission in park since the tranny's output shaft wouldnt be turning while in park.

Those NP246/E Tcases are stupid easy to rebuild. You can buy a replacement rear case if your forward half is good. Otherwise you are best off just buying a rebuildable core and rebuilding it with new clutches, pump rub plate, chain, bearings and seals unless you plan on spending the money on already rebuilt unit.

 

[Matthew Jeschke]

" I removed both driveshafts from the truck and put the trans in neutral. This resulted in the same sound I had been hearing while driving, except this time obviously I wasn't moving at all."

If your transmission wasnt in a gear then its output shaft was NOT turning so the input shaft of the Tcase wasnt turning. That rules out your Tcase. Your noise is coming from the transmission or engine. Your torque converter and tranny pump is always turning no matter what gear you are in or even neutral, as long as the engine is running.

Front diff ruled out since you were in neutral.

Your noise could be coming from the engine or accessory drive.

Problem isn't your tcase. It is the transmission. If makes noise in neutral or park. Drop service pan... see if you have clutch material in there or metal parts. Or something on the accessories. Power steering pump can make a dreadful noise too if it's going out.

The 4l60e likes to push one of the checkballs through the selarator plate. If you catch it quickly enough you can drop the valve body, flatten back the separator plate and put in plastic checkballs...

However if you have metal chunks and or lots of clutch material in pan you will need a rebuilt transmission.