Drive train vibration at 55 rpm

[Chuck Step-a-side]

I have a vibration or low to high rumble that happens every 3 second continually when driving around 55 rpm or higher.  It feels like it’s coming from either the drive train or transmission.  No vibration is felt while driving under 50 rpm.                                                                                                                                     
My 1984 2 wheel drive Stepside was sold to me with a 350 LG SG1 (which is a 350 w/center bolt valve cover) and serpentine belt drive from 1989 S10, and Turbo 350 transmission. After purchasing this truck last year; I have replaced the front and back universal joints, transmission mount, front and rear transmission seals, upper and lower ball joints, check the engine motor mounts, check front and rear brakes and bearing play. If anyone has any idea on what to check or recommendations, please let me know. Thank you

[philo_beddoe]

Thats how things started with me, read "bad vibration", 5 months later, a new crate 350 fixed it. A new crate engine fixes everything. Anyway, really hope it is something easy and not your crank.

Keep us posted.

[jg1977c20]

where do you feel the rumble IE in the seat , the floor or ??   how worn are the front tires or how old are they and has the balance been checked lately ?

[Irish_Alley]

is your drive shaft phased correctly?
do you have a one or two piece drive shaft?
does it get worse at a higher speed?
does it do it when youre coasting?

[philo_beddoe]

is your drive shaft phased correctly?
do you have a one or two piece drive shaft?
does it get worse at a higher speed?
does it do it when youre coasting?

Deja-vu Irish, you asked me the same questions about 5 months ago when my problem started! Glad thats over.

[Irish_Alley]

Yeah. Like you said hopefully it's something easy

[Chuck Step-a-side]

Guys,
 I believe it's coming from the drive shaft or the transmission. It's like a low rumble feeling coming from the body below when driving. Can you explain "drive shaft phase correctly"? Thank you for the follow up.

[philo_beddoe]

Guys,
 I believe it's coming from the drive shaft or the transmission. It's like a low rumble feeling coming from the body below when driving. Can you explain "drive shaft phase correctly"? Thank you for the follow up.

In my "bad vibration" thread, i believe it is explained and illustrated. Irish posted it.

[Irish_Alley]

Drive shaft phase

[Chuck Step-a-side]

Got it. I knew there was something to align when doing the universal joints and that one slipped my mind. I'll check it this weekend and let you know what I find. Thank you.

[Greybeard]

Correct me if I'm wrong Irish but won't being out of phase start as soon as the driveshaft starts spinning?

I just had something like this happen to my car, over 55 vibration that sounded like it was coming from the drive train, new shocks fixed it. A wheel balance didn't hurt either. The right rear tire was just enough out of balance to overwork the shock and start bouncing at about 55 mph. This created a subtle but very noticeable vibration and a slight noise. Of course, the car has small tires (all four would likely weigh just slightly more than one truck tire)  and coil spring suspension so YMMV.

One other thing I have had happen, check for broken belts/sidewalls in the rear tires.

[Irish_Alley]

it could if it had enough mass to be out of balance that bad. just like wheel weights its not enough to wobble as soon as you take off but after a certain rpm they will straighten out and then they will start to wobble.

[Greybeard]

Another question, wouldn't being out of phase cause jerking (and a possible ticking noise), not an imbalance? The u-joint(s) will bind every quarter turn (each) creating at the minimum 8 jerking cycles per revolution as each bearing side binds. At a slow shaft speed that would be in the feel of jerking sensations, which would get progressively worse as the rpm of the drive shaft increased. I left a u-joint go once until a bearing cap at the diff housing had disintegrated, and it started jerking. Not quite out of phase, but certainly not still in alignment.

Or not....

[Irish_Alley]

i had some bearings in one joint go before, it caused a ping going into reverse or on a load. ive also had a 2 piece out of phase and a bad carrier bearing that would vibrate under a load. fixed them both at the same time so im not sure which the problem was but it was fixed

[Greybeard]

Yup, I just wasn't sure out of phase would cause ONLY a high rpm vibration. It seemed to me that would need something heavier, like a tire or something. But in the case of Phils problem it turned out to be the crank thrust bearings. Makes me wonder if I didn't dump the 454 I had in my current truck wrongly. I had a knocking noise that sounded like a rod bearing but after getting all my hot rod friends together and going over it with a fine tuned screwdriver hearing device, the conclusions where indecisive. Then we took the converter off and started it and still could not isolate the noise. We never even considered crankshaft end play I'm sorry to say. I just pulled the engine, traded it for a good hi-alloy four bolt main block and and crank and went from there. I still put $3500 into the engine sitting outside because I thought a BB would cost too much to rebuild. That was about ten year ago, now the engine has about 1500 or so miles on it. The one in my avatar picture to the left...live and learn...