Vibration and loud noise under DECELERATION

[K9-K141]

Hey all
2005 f350 cc sb 6.0, Manual 4x4 shifter, 8 inch fabtech

While driving on the highway, typically over 55-60 mph, when i let off the gas pedal i hear a loud winding coming from under me it sounds like, and the 4x4 shifter vibrates like crazy, then you hear it almost spin to an abrubt end and when your rpms or speed drops a few it stops. It will also stop if you put it under load again by getting on the gas. When it happens I usually give it some more throttle and it will immediately stop, sometimes if i ease off the throttle keeping a load on the truck it wont happen or wont be bad. Rarely it will just happen while cruising on highway, but i can make it happen by simply getting off the gas. The engine rpms dont skip a beat and motor sounds strong, tranny sounds strong and doesnt have any issues shifting, and again, when i hear and feel this noise i dont see the rpms fluctuate, its just a loud nasty vibration i can feel in the 4x4 shifter and under my floor board. I had the carrier bearing replaced and the driveshaft rebalanced, ( shop told me it was off, shop also told me universals are fine, its the same shop that does dennis andersons trucks). Im lost, Also, I Took front driveshaft off and it didnt change a thing, i locked hubs and it didnt change anything. Any clue?

[thomaslord84]

Sounds like a torque converter to me. I have a '94 F-150 that did the same thing, I replaced torque converter and it was all good. If that is you problem you should address it quickly, because the metal shavings that are coming out of your converter will cause your tranny pump to fail which will total the whole tranny.

[K9-K141]

i thought the same, but after messing with the driveshaft and carrier bearing it has dramatically decreased, and it only happened after the lift was installed.

[06SuperDutyF250]

if your driving at highway speeds, usually the converter is locked up, transmitting all the power thru the tranny, when its not locked, it has a bit of slippage, which is normal. But if your letting off the throttle maybe the converter is unlocking and the noise is going away. So maybe a lockup issue? Did you re-gear the Diffs when you lifted, if not with an 8" Lift and im sure your running 37's tires at least, your engine and tranny are being lugged, maybe causing the winding noise. Might be the front driveshaft spinning somehow, its also at a crazy angle im sure

[K9-K141]

nope did it with no front ds on it

[f250ghost]

Did you ever figure this out? My 6.4 is doing the exact same thing

[twoicebergs]

There is no doubt the drive-line angle will cause noise and could be worse with flutter (loose drive-line) at power off at speed. Did you realign the axles to match the lift? As well, did you correctly lengthen the rear shafts to ensure the right amount of overlap on the slip-joint.

[f250ghost]

It did this before I lifted the truck, but went away and is now back. We did get everything aligned...but I'm gonna buy an adjustable track bar here in the next couple days because the axle in the front is slightly shifted to the left...but I don't think that's related to it at all..especially since it did this before I lifted the truck. Something else that puzzles me is that the tranny was low on fluid...but my buddy last night brought up a good point when he said the driveshaft comes out of the T-Case....which has a different fluid in it. So now I'm wondering where my ATF went. I'm gonna check it again today..its possible the dealership under filled it. I guess...the more I think about it the more I wanna take it to Ford so they can fix it. I'm only 2000 miles away from the tranny warranty expiring :-(

[twoicebergs]

I was wondering about the transmission, tail bearing (even seal). You didn't indicate you had a fluid leak (missing fluid), but the vibration could be other internal damage. A few months ago a member had a shaft rub through the top of the transmission that was hard to find at first. Maybe a mirror and light are needed.

One more thing, you might want to see how much fluid you now have in the TC.