crew cab 2wd vibration

[crewcab higgy]

My truck has had a slight pulsating vibration at highway speeds hardly noticeable. I put my new motor in and drove it last night and the vibration got worse. Before it had 2 worn out*motor*mounts*and now it doesn't but idk what it could be. It happens on the throttle at highway speeds in third and feels like I'm hitting the rumble strips in 1/2 second on off pulses in 3rd. In second it vibrates bad at above 2500 rpm.
It's bad enough I'm considering towing it to a shop but I'd like to make sure I'm not overlooking something.
Also 454*th400*dana 70 combo

 

[da_raabi]

Driveshaft problem? Does it vibrate at all if you rev it in park or neutral? Or is it only while driving? Does it happen around town stop/go at all? If you have the crew cab long box like me then you have a HUGE drive-shaft (heh heh - gotta be careful saying that around here) and its probably got worn universals, center bearing or it could even be out of balance. At least that's what I'm thinking. These shafts are so long they really need to be perfect!

 

[PrairieDrifter]

I would say driveshaft issue or hanger bearing, you could try replacing your transmission mounts also. Another possibility could be you may have lost a wheel weight or your tires are just out of balance.

I had a pulsating vibration on my Colorado last year and it turned out my front diff was shot it wasn't a bad vibration but you could definitely feel it and for sure hear it.

 

[crewcab higgy]

The trans mount is good I was thinking the shaft too I'm calling around after work to get prices on balancing. I have a new carrier bearing I'm also thinking that I might have not installed it squared up.

 

[crewcab higgy]

Oh does not do it in nutral and if I pop it in nutral on the road when it's doing it it goes away

 

[crewcab higgy]

I think I found the culprit

I did not know it mattered how the tc bolted to the fly wheel. Turns out I was wrong. After u joints an and inspecting the diff and checking every thing else I could think of this seems to have fixed my problem. I unbolted the tc spun it so the weight on the tc and weight on the flex plate were opposite of one another put it back together and it seems to be good now.