drive line vibration

[69GWC]

My 69 has a drive line vibration and it happens at 2,000rpms to 2,200 rpms and it does not seem to matter which gear its in but it gets worse with a trailer in tow. If I stay in 2nd gear and stay at that rpm the vibration will just stay there (no worse no better) but all I have to do is speed up to get over that rpm range and its gone.
It has a 465 4sp, Rockwell 221 and a completely rebuild 12 bolt (vibration. Was there before it was gone threw) and also has a one piece shaft in it.

My plan is to install some new u joints allthough the ones in it dont feel to bad, but was wondering if I should think about having the drive shaft re-balanced of if anyone else had a thought about the vibration iam having.
Also have new wheels and tires and still does it, all new fluids in the tranny, TC and rear end.
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[ole dollor]

if you think its your drive shaft, just pull it out and have a drive line shop see if its balanced. that would be the best way to find out, also if the u joints were bad they would find out also...that is where i would start...

[69GWC]

Yeah thats just my guess about what the vibration is from and wanted to see if others thought that sounded like a possibility before i spend the money getting someone to balance it.
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[jd7]

its happening only during acceleration .... if you take your foot off the peddle does it stop vibrating ?

[geezer#99]

Check your pinion angle is equal to the centre line angle of your motor.

[69GWC]

It seems to happen on or off throttle but it does it for a short rpm range and seems worse if you lug the motor down like if you in 4th gear, I say worse but its just a small change if any. Now if i push in the clutch it goes away,
I guess I should say it only does it under load at 2,000 rpms

I did lift the truck 2.5" with just blocks in the rear but it did this when it was setting at stock height as well. The lift blocks are tapered to correct angle and they are installed correct allready double checked that.
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[brad_man_72]

Driveshaft vibration will vary with vehicle speed not engine rpm. You have a problem before the transmission. Clutch, flywheel, crank, or ballancer.

Driveshaft out of ballance will usually show up at 2000-2500 rpm in whatever gear is 1:1. Driveline angle problems will show up at speeds of less than 5mph.

I've been building/repairing driveshafts for about 5 years in a driveline specific shop.
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[69GWC]

So are you saying you think its the drive shaft out of balance then? Or something in/on the motor. Because it vibrates right at that rpm no matter the speed but also does it in 3rd and 4th gear never felt it in 2nd gear but you go by that rpm really quick in 2nd.
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[biggestjohn]

If it occurs at the same rpm range, no matter what gear, that would indicate that it is engine/trans related. Those are the only things that are at the same rpm. The drive shaft will increase rpms as speed increases. U joints usually vibrate violently under deceleration. Sounds more like a flywheel/clutch problem, maybe clutch slipping, or flywheel out of balance. It doesn't sound like your hitting a certain harmonic range, due to it vibrating worse if you lug the engine, plus it stops if you push in the clutch, so I doubt its a balance problem.

My guess, clutch slipping.........

My 2 cents............

[cdowns]

i'd have the tires balanced by someone who is used to doing big ones like that

[69GWC]

It did it with the old tires and wheels, I had a good tire shop install and balance the new tires and wheels and it still does it pretty sure thats not the issuse the shop i use is real good with large tires.
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[Daves70]

Seeing as how it is based on rpm and not speed I'm guessing a bad clutch or pressure plate or the engine is out of balance (externally balanced flywheel or balancer on your internally balanced 350)but if it goes away when you put in the clutch I'm leaning towards the clutch. One other simple check would be your motor mounts.

[69GWC]

Cool I will look at the motor mounts and see if they have any movement, my luck it will need a new clutch as that would not be to much fun for me to do..lol I will just pretend its not the crank out of balance........
Maybe I will install a new balancer on it and see if that takes care of it.
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[69GWC]

Well my vibration keep getting worse so I yacked the drive shaft and took it up and had it rebuilt, I noticed when I pulled it out that the slip joint had developed a good bit of play that it did not have (or i did not noticed) before.
The drive line shop said it was pretty bad and they replaced the complete slip joint, both U-joints balanced and painted the shaft so hopefully this was the main problem and my vibration will be gone.
I did not get to drive it today to test it so hopefully tomorrow i cant and see if it fixed it.
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