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Rumble from ~30-40mph need some help diagnosing

Hey all, I need some help. I have a 1993 ford f250, 4wd, manual transmission with a 351W, about to turn over 158,000 miles.

When im in 3rd/4th running 1300-1800rpm or about 25-40mph I get an odd rumble; kinda like the rumble strips on the side of a road but not as rapid and it sounds a lot deeper. Its not from the steering wheel or when im
Braking, just maintaining speed or accelerating. The sound seems to shake the whole truck; coming from underneath albiet I can’t pinpoint the source while driving.

This upcoming weekend im getting the tires rotated, i should be able to pull them prior and get a good look see as to whats up.

Ive checked the driveline/u-joints, and steering components; that all seems good. What else (in order of severity and cost) should I check?

Brakes, wheel bearings/axle components, spark plugs, tranny, what else?

One other question: ive been given recommendations for how to check u-joints, and ive checked it every way. Whats the correct or way a mechanic would do?

Have someone inspect the center driveshaft bearing.


Have you checked the oil level in the gear boxes, Transmission, transfer case, front and rear diffs ?

Tester; im assuming you mean have a shop test it?
How do you test it?
I have access to one of those fancy dancy DIY shops with pro supervision. Courtesy of the military; so I do all my work except for major PIA and tire alignments there. One is just because sometimes its easier to hand over the keys, and the other is the one thing they don’t have the capability of.

I have not; granted im stock piling ATM to change everything over and grease the joints that can be greased.

Torque converter shudder was a very common issue during this era and was in most cases caused by aged transmission fluid. Try doing a complete transmission fluid exchange and see what happens.

In some rare cases a new torque converter may be needed but i wouldn’t worry about that at this point.

Edit Never mind. I wandered off track mentally and was thinking automatic… my bad.

Regarding U-joints many assume that if the shaft feels tight this means the joints are good. That is not necessarily true.
Sometimes it requires removal of the driveshaft so the joints can be examined physically by hand.

In many cases the front joint is the one at fault.

Assuming that Tester was referring to the carrier bearing, I’m inclined to agree that it’s a good place to start.
To the OP: that’d be the bearing in the center of the driveshaft that holds up the aft portion of the foreward shaft. Checking it is as easy as simply grabbing it and shaking it vigorously looking for play. Aft of the bearing is a U-joint that should also be checked, as should all the U-joints in the powertrain.

If there’s been any work done affecting the carrier bearing, definitely a suspect. That part can get re-installed out of alignment and cause weird vibrations. I’ve always been successful checking the u joints on my own ford truck just by crawling under there and manually twisting on the driveshaft while I watch the u-joints. If there’s any play at all, the u- joint has to be replaced. I don’t think it is any of these though. My guess, there’s a rattling in the exhaust system that gets enhanced at certain speeds due to the sympathetic vibration phenomenon. Check all the exhaust hangers and the cat heat shield for robustness. Good idea to check the engine and transmission mounts while you are looking.