Transmission or transfer case

[waynep]

1997 Sub, 3/4 6.5 TD, 180K miles. TH 400 E.

Something under truck, I believe in transmission or transfer case, makes strange noise, crunching gear like, now and then. Not U joints, and I disconnected rear driveshaft and operated on front wheel drive only and it still makes the sound. Any ideas for eliminating either the transmission or transfer case?
May only happen in OD but not sure?
Any troubleshooting info appreciated. No codes.

Thank you Wayne

[DaveBr]

You could try blocking your rear axle housing so your tires are off the ground and putting the truck in gear so your tires are free wheeling. Get under the truck with a stethoscope and locate the origin of the offending crunch. I hate the crunch sound. It always sounds expensive.:eek:

[DmaxMaverick]

By the time you can hear an auto tranny making "crunching" noises, it's a matter of feet and minutes/seconds, not miles and days/weeks. That leaves the transfer case, flex plate, torque converter housing, in that order (according to most common failures). Other components make the list, but you've eliminated them by running with the driveshaft removed. This assuming the front end/drive shaft was not engaged before (otherwise, it would also be suspect). A noisy transfer case will normally show wear materials (like pieces of roller/needle bearings, gear teeth, etc.) during a service. Check the drain plug, it should be magnetic. A cracked flex plate can be very hard to see while installed, but check anyway. Check the torque converter for cracked or detached mounting lugs and/or loose/missing bolts. The torque converter housings can crack, but will almost always leak ATF and make a big mess you can't miss.

Also check your torsional damper (harmonic balancer), crank pulley, and all the belt driven accessories, just for the heck of it.

TH 400 E ?? You should have a 4L80E.

[waynep]

You are exactly correct, I have a 4L80 E transmission, not a TH 400.
I tried running with rear wheels off the ground and the outcome was not conclusive.
When it happens, it kinda feels also like a slight slipping sensation.

Thank you All, Wayne

[DmaxMaverick]

If it's most noticed in OD, like a growling/chattering sound (and feeling) under light to moderate load, it's probably the tranny. It could also be engine or tranny mounts (worn out, they can allow other components, like exhaust pipes, to contact the chassis when the drivetrain torques).

[kaylabryn]

I know the Flex plate is prone to cracking, I have heard the sound described everything from cracking, snapping to grinding. They usually crack at the bolt holes. If bad enough you can inspect with removing cover and check, if it is a small crack you will only see if you drop Trans. This cracking is not that uncommon, I would check this first myself.

Mike

[rameye]

I put my money on the torque converter preparing to meet is maker...

The sympoms you describe are the cool things mine was doing..

Bad news is...when the converter implodes it spreads all sorts of nasty thru the whole tranny.....so get ready.

On the good side...Zoom makes a great shift kit for the 480L...gets you some nice positive shifts....no wandering.

[waynep]

Hello All:
Just tried it again and it feels more like a slipping than a gear noise. Happens in all gears it seems, and it usually happens twice, about 2 or 3 seconds apart. Feels like a clutch is slipping a bit in a manual??

Almost feels like real bad universal joints, but removed rear drive shaft and joints are fine.

Any and all input appreciated. Wayne