I have a '79 F-150 4x4 with a 351m, NP205 and a C6, my truck has been shaking and vibrating at various speeds. It shakes bad from 0-20mph, then not so bad from 20-40, then stops after 40 when my foot is on the gas but then shakes bad when I let off. I put in new plugs, wires, cap and rotor, compression test was anywhere from 118-130psi. I tried two different drive shafts (u-joints are good), engine and tranny mounts seem ok (not moving around or missing bolts). Timing set to 14°BDC on the marks so I don't think it's the balancer. The tires are old but when I put it in neutral it gets less noticable, just put new ball joints, tie rods, and wheel bearings. I have a clicking sound coming from the bell housing, so at this point I'm thinking maybe the torque converter? Can a torque converter shake the entire truck? FTE is about the best thing ever and I can't wait to see what everyone comes up with. Thanks!
Matt

 

If its a semi-violent to violent shake....its most likely the track bar bracket/bushing.Its very common for those to wear and cause a BAD shake.

The easiest way to check is to have someone rock the steering wheel back and forth,while you look at where the track bar and bracket bolt up.There will be noticeable slop if thats the cause.In some cases you can rock the wheel back and forth yourself and notice the whole nose sway side to side.

If thats not it...Id look into the radius arm bushings next---but my money is on the track bar bushing.Good luck!

 

Sounds to me like you have it narrowed down to a "high frequency" engine or driveline vibration. Narrow it farther by kicking it out of gear and reving the engine and see if the vibration is there. If it is the torque converter it should show up. And yes, a torque converter or flywheel will cause vibrations.

 

What size tires are you running? Could be the steering damper is pooched. Check the drivers side frame just on the front side of the steering box for the famous frame crack.

 

Could be a loose rear transfer case bearing.

 

you mean other people have had the crack in the frame on the front side of the gear box?! i didnt even know mine was until i was installing my lift, and had to take off the front shock tower, and behind that was actually a couple cracks. put a dent in my estimated finishing time having to repair the frame, but, im GLAD i caught it.

my truck vibrates too, but only when giving it the skinny pedal treatment. i'm letting it go til it gets unbearable ha

 

Thanks for the input, I think is is definetly think it's in the "high frequency vibration" category. Already fixed the cracked frame LOL!!! and probably need to look at the track bar bushings so I can keep it safe on the road. Raytasch, when I kick it out of gear it still has the vibration, I'm trying to isolate it to either the engine of tranny at this point. The engine hardly vibrates when it's idleing, I would think if the vibration was coming from the engine I could at least see it. When I put it in drive put my foot on the brake and hit the gas it feels like the truck is going to shake apart!

 

Before I went tearing in to the TC, I'd have a real good look-see at the front end, and make sure everything is greased and in good working order...remember, a couple little problems can culminate to one big problem. I've had shock towers come loose that caused vibrations...and I think an extremely overlooked part is the axleshaft u-joint.


That said, checking that stuff is free, and I figured could be ruled out...but it does sound like a potential TC issue to me.