Vibration
 

I have a ‘47 1/2 ton, period correct v8, 3spd manual, 4.11 banjo. Has a bad vibration just before I shift and at speeds above 45 mph. It makes no unusual noises. Motor mounts look recent, no excessive play in unjoints. The transmission mount is weathered but I cannot shake it by hand. I intend to start with the trans mount (unless other suggestions). Are there torque specs on the bolts?

Re: Vibration
 

Did this just start happening at once or has it been coming on slowly over time and getting worse? Tim

Re: Vibration
 

I just bought the truck from a broker and, unfortunately, I donÂ’t know any of its history

Re: Vibration
 

Does it vibrate if you rev the engine with the clutch pressed or the transmission in neutral?

Re: Vibration
 

No only while moving with trans engaged

Re: Vibration
 

Does the vibration go away above 45 mph?

Re: Vibration
 

does the vibration come thru the steering wheel? the seat of your pants? I would start with universal joints, then check input shaft into rear end, or have the driveshaft balanced--look for any weld marks to see it threw a balance weight

Re: Vibration
 

I’m with Alan , I’d be taking a good look at the u - joints. It’s gotta be driveline related.

Re: Vibration
 

OK, thanks guys, that gives me a good place to start. Think I’ll still change tranny mount as it looks pretty rough. Is there a torque spec?

Re: Vibration
 

There probably is a real torque spec. The shade-tree spec is a good hard one hand pull on a 10" ratchet handle. Maybe 20 ft-lb.

Re: Vibration
 

Well... I have been puzzled with vibrations like this many times only to finally figure out that I had tire issues. Tread separation. Just another item to check. Good luck.

Re: Vibration
 

If the vibration happens at a certian speed (eg only vibrated from 45 to 50 but over 50 its gone) its drive shaft related. If it happens at a certian rpm only while moving its transmission related. If you have it while not moving its motor or clutch related. If you have it all the time while moving and gets worse the faster you go its wheel related.

Re: Vibration
 

Thanks. Logical diagnostic is exactly what I need. It sure sounds like transmission but to be honest I havenÂ’t tried to go faster than the vibration start point because it shakes so bad. I guess IÂ’ll know more when the new mount arrives. BTW IÂ’d like to see some picks of that 1 ton project.

Re: Vibration
 

I'd start with the u-joint(s).

Re: Vibration
 

Me too
So you got it with the vibration so with no history I would check the U joints and then see that the driveshaft is straight and ballanced. If that all checks out swap on a different set of wheels if you have them or can borrow them.
Clutch or input shaft vibration is there in every gear in the same rev range and trans vibration magifies the the faster the output shaft spins unless the vibration is in the lay shaft then it will only appear in the lower gears and not top gear 1:1

Re: Vibration
 

Sounds like a plan. I’m going to drop the driveshaft and change u joints at the same time I do the trans mount. If that doesn’t do it I’ll have the driveshaft balanced.

Re: Vibration
 

WHAT is the frequency of the vibration? It MIGHT help to try to narrow it down to the area of the vibration via the frequency of the vibrations. There are no guarantees as to whet I am suggesting, but does the thing vibrate at (for instance) the speed of a tire going around and around, or at the speed of a driveshaft which could easily be three or four times the speed of a tire rotating? Or does it even change with engine speed? Get what I'm trying to say? It might be a little more methodical to approach this using all the clues at your disposal rather than just grabbing at straws in the dark.

Coop


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Re: Vibration
 

I doubt it’s wheel/tire related as there is no vibration at low speeds and seems to be more dependent on engine RPM; at shift points and above 45 mph in third. No tach installed at this time however by my calculations 275 60 15 tires with a 4:11 gear would produce a driveshaft rotation in the neighborhood of 2220 rpm at 45 mph which would also correspond to a reasonable shift point.

Re: Vibration
 

check your u joints, i had the same issue on my 37 sedan and it was the u joint in the clam shell. shot a slurry of low melt grease and gear oil and it was gone in a mile of

Re: Vibration
 

I had a vibration in my old truck a while back and spent a bunch of $ trying to fix it. To make a ling story short, it turned out to be flat spots on the tires from sitting for long periods of time. After a 10 mile drive, all was well.