Grinding/vibrating on decelleration?

[f250ghost]

So...my truck used to grind/vibrate somewhere in the drive train when I let off the throttle around 55-65 mph. It seemed to do it when the torque converter would unlock (according to the MiniMaxx)..but was intermittent. So I took it to the dealership...they couldn't find any codes or issues and said there was nothing wrong with my transmission or torque converter. The problem suddenly went away. Well here we are a few months later...and the day after i instelled my lift it..it's back. Only now...it does it around 55-65 whether the torque converter is locked or not...sometimes I even hear/feel it when Im on the throttle and the RPM's are at a sweet spot. I'm starting to think I have a hub that's stuck locked...or something might be loose somewhere. Any one else had this? The truck shifts fine...turbo works great...etc. I'm gonna be re-torquing everything in the morning to see if that fixes it...just thought I'd see if anyone else had this problem?

-Ben

[K1LLsW1TchEd]

make sure your shackles are tight on the rear axle, also check the driveshaft for play. also changing the angle of your driveshaft when lifting a vehicle changes things too. are the blocks angled or did they send you a shim kit?

[f250ghost]

The blocks are angled...but they're in the right position. I'm due a re-torque next week hopefully that fixes it...but its getting a lil worse.

[K1LLsW1TchEd]

Could be a bad tranny mount, leaf spring broke or cracked, or the drive shaft out of balance. Hmmm?????

[f250ghost]

The leaf springs looked good when we installed the lift...it did it a little before I even lifted the truck but Ford said they couldnt find anything wrong with the tranny...but IDK if they looked at the tranny mount. How could I check that? I dont think it's the driveshaft...it feels like its right under the floorboard in the front of the cab.

[K1LLsW1TchEd]

If its in the area of the floor board it may be a tranny mount or a bearing is going bad in the tranny

[f250ghost]

Hmmmmmmmmm Id hope not on a 50k mile truck!

[f250ghost]

Well guys I spent the morning going over the whole truck trying to find out what the hell is going on and I think i may have found it. My rear output seal (where the driveshaft goes into the rear of the transmission) is dry rotted and has multiple cracks. There's also transmission fluid residue on my exhaust, body, fuel tank, and frame underneath the truck. So I checked the tranny fluid...(which I had just recently checked...) and it's dry...as in nothing is on the dip stick when i pull it out. I've tested it three times with the same result.

I'm wondering now if the Dodge dealership didn't under fill my tranny when they had to repair a leaky transmission line when I first bought the truck. I've also taken it to Ford once before a few months ago about it and they said they couldnt find anything wrong...so it's on record that I've had issues with it. Gonna go buy some fluid and top it off then see what happens....looks like a trip to the dealership next week???

[K1LLsW1TchEd]

Yikes. Add a quart and check it. Add and check again. Some guys on here put an extra quart in for better shifts.

[f250ghost]

Topped it off and it still does it...now im starting to wonder if it really is the trans or something different...so if it was the trans, there should be some metal shavings correct? Tryna narrow it down...Ford already told me months ago they couldnt find any issues...only 2k miles left in the tranny warranty!