Have a 1988 F350 Crew Cab, 4X4 with 7.3 IDI non turbo.

I have noticed at funny sound in when I start out cold. It starts rolling fine, then it seems when I let off the pedal I get a rumbling sound somewhere under the drivers side floor pan. It sounds like gears rumbling. As the truck warms up it seems to go away. I can't locate it. I was thinking u joints or transfer case or a hub, but they are manual hubs and seem to lock and unlock okay. It is worse in the cold. Wondering if anyone has had something similar that can point me wear to start looking and how to figure this one out, it is hard to pin point since it only is when I am driving, so I am sure it is in the rolling chasis.

Any ideas?

PW

 

Sounds like a u-joint gettin' ready to cause problems.

 

What transmission do you have?
If it is a manual, grab the shifter and see if you feel it there.

 

I would jack up the wheel and check for bad bearings by wiggleing the wheel. If you have the manuals locked in but transfer case in in 2H then the front axle and driveshaft are turning all the time. I would check all the universals first by viewing for black dust/rust around the cup then by trying to wiggle the shaft looking for loose parts.

Check your spring attachment bushing right under your feet for worn out and the sprong curl vibrates on the hanger and floor at your feet.