Vibration

[low79fx]

Ok,I'm coasting down the Interstate reaching about 55mph thru about 70mph,and I start notice this hi vibration coming from around the floor board area under my feet to about under the seat.My first guess is u-joints or tranny mount.Has anyone out there come across or experience this in these old but hell can't keep your hands off of trucks.

[drbyrdman]

rotate the tires and see if it goes away. first thing i would try

[monolith]

If you have a 2 piece driveshaft- you may want to also check the driveshaft center support bearing and cushion.

[low79fx]

Brand new tires,mounted and balanced.One piece drive shaft.

[rwolf9653]

Originally Posted by low79fx

Brand new tires,mounted and balanced.One piece drive shaft.

The new tires is even more of a reason to rotate them and see if it corrects the vibration. You could have a bad tire or a bad balancing job even though they are new.

[MacAttack]

Piece of heater hose, an assistant, and another test drive.

Have your assistant drive - at the designated speed - set on the passenger side, with the hose held up to your good ear, with the other end on the floor and move it around until you discover where it's the loudest.

(Complete this process with your lady as your driver - to keep people from giving you funny looks - if you've only got a short piece of hose.)

Mac.

[markeb01]

I'd be inclined to look at the tires first also, and if this is being tested first thing in the morning, it could be flat spots in the tires that haven't warmed up yet. Mine use to to this during the winter for the first few miles it was on the highway until they warmed up.

My experience with bad u-joints is normally a growling noise, without much vibration - unless one or the other is "really" bad.

Another consideration is engine vibration. I had a 350 Chevy Targetmaster in my 46 Ford sedan and it vibrated between about 2200 and 2500 rpm. I've had a second Targetmaster 350 in my 1960 GMC for almost 20 years now, and it also vibrates in the same rpm range. The factory balance (or lack of) is pretty sad in these inexpensive crate motors. It's easy to check - if you have a stick, drive to the high end of the vibration speed and briefly push in the clutch. If the vibration stops (and your u-joints are good) the poor engine balance may be causing the car vibration. Same thing with an automatic, just run up to the high end of the vibration speed and put it in neutral for a second. This should isolate chassis versus driveline.

If it's not the driveline and it's not the tires, the shocks and the shock mounts should be checked. Not sure what year your truck is, but the 63-66 series have a history of cracking in the upper front area where the shock stud mounts to the frame.

[low79fx]

Well after going over my vibration problems yesterday I discovered I had a busted tranny mount.No rubber intact to hold itself together.I took out mount removed what rubber was left,cut a piece of 2" metal bar and converted it to a solid mount.Test drove it and it did cure the better part of the vibration.Still had a little left so i started looking into u-joints.Took the the rear u-joint u-bolts loose and tried to slip drive shaft forward out of the rear-end yoke.It would not move,looked at front yoke and noticed yoke already all the way in the tranny,no movement at all.Thus I believe this is where my vibration is coming from because I can feel and hear it coming from the transmission and drive shaft.I noticed that the motor mounts were swapped lft.to rght.,rght.to lft.making engine sit 1" backward.Swapped them to correct side and it moved engine forward giving me the clearance to be able to slip drive shaft forward and remove.Well I'm still working on it today,I'll let you guys know how it turns out when I finish.

[padresag]

eng mounts will do it and put a proper insulator back i n that rear mount. the solid one will still cause vibration and promote stress
ron

[protrash64]

Good you caught the mounts. A rearend/driveshaft combo too tite to the trans can hammer a trans to pieces along with the rearend. That extra engine space will save you a bunch of money.

I think you probably just discovered why some people cant get their dizzy's to fit, too.

[markeb01]

If you're going to keep the solid trans mount it's important to also change to solid motor mounts. Having just a solid mount under the transmission is likely to crack the case over time.

[low79fx]

Yeah,thought about all those scenarios.I was just trying to isolate and pinpoint the problem.I will replace trans mount with rubber one again.

[low79fx]

Replaced tranny mount with a new energy suspension one, got everything where it is suppose to be.I busted the u-joints out and yes they were trash,the front one was falling apart,needles had already fallen out,they looked as if this was the first time they had been changed.So I believe I found my problem,a combination of tranny mount, u-joints and zero clearance between drive shaft and tranny.Once I replace the rear tranny seal and replace the u-joints I will see how she acts.