Heavy vibrations
 

Hello, seeking some knowledge from some of the c10 masters! I am having a problem where I am getting a bad shaking/vibration. It the feeling is not in the steering wheel and feels to come from the rear but i may be wrong. So far I have been throwing money at it to try and solve it. I have installed all new u joints, carrier bearing and had it balanced. New tail shaft housing bushing as there was a bit of play. Had new tires put on and balanced twice. Transmission mount is in tact and seems ok. This happens like clockworks at 2300 rpms only in 3rd gear. If I accelerate hard and get up to 3500 rpms I can feel it shake at 2300 as the rpms drop. It only does it in gear and only in 3rd. Thanks for the help.

Re: Heavy vibrations
 

Welcome to the board from TN !

What youre describing is a harmonic vibration. What I mean by this, is at a certain RPM of the rotation of the drive shaft you'll feel the vibes, but not at others.. and it happens every time the RPM reaches that point. Usually it's 64mph but tire sizes and things like that can change that too.

My first question - is the truck lowered at all? Raised ?

What were looking for is the angle of the drive shaft in relation to the trans tail shaft. , as well as the pinion. Is it a two piece drive shaft ? You mentioned a carrier bearing, I am assuming long bed, 2 piece drive shaft.

I'll watch the post, we'll get it figured out.

Re: Heavy vibrations
 

Coil or leafs?
Have you checked pinion angle?

Re: Heavy vibrations
 

The truck... well actually suburban but more traffic over here! Anyways coils and no it is not lowered. I do plan on lowering it some here in the future when budget permits. In preparation of lowering it I did add a shock relocation kit from ece with their lowered rear shocks already and their adjustable pan hard bar. The rear end is centered right now. I have not yet checked pinion angle I figured in stock form it should be fine?

Re: Heavy vibrations
 

Here's a pic to better visualize what I'm trying to explain. When you lower, and/or raise a truck the angle of the pinion vs. the transmission tail shaft, etc. they really need to cancel each other out. I usually run my trucks at about 1 or 2 deg in the rear. You dont want it at dead nuts 0 deg.

https://www.hotrodhotline.com/md/htm..._harmonics.php

Re: Heavy vibrations
 

Stock transmission mount ?

Re: Heavy vibrations
 

I think so... the truck was a 6cyl and v8 swapped at some point

Re: Heavy vibrations
 

It could be the motor mounts, trans mount, it sounds (to me) like the drive shaft / pinion angle is out of whack. I think my next purchase would be an angle finder and just see what you're working with before you pit any more $ into it. On the up side, you have a bunch of new stuff to set it right on.

Re: Heavy vibrations
 

I have a digital angle finder so I will check the pinion angles and report back sometime tomorrow. I agree most everything probably needed replacement anyways! I want to make sure I get everything driving smooth before I modify anything. Thanks for the suggestions it has been driving me crazy!

Re: Heavy vibrations
 

I would check the harmonic balancer to make sure it is the right one, it is in good shape, and it is tight. Also could be the wrong flywheel/flexplate.

Re: Heavy vibrations
 

I checked the angles and I am at 7 degrees down from the output shaft and 7 degrees up on the pinion flange.

Re: Heavy vibrations
 

Did you also check the angle of the driveshaft? I am not as familiar with suburbans but as asked will that be a 2 piece driveshaft?

Re: Heavy vibrations
 

Stoked on this link! ADMIN PIN IT.

Re: Heavy vibrations
 

Measured from the middle of the shaft the front is at 5.5 degrees and rear is at 4.5 degrees.

Re: Heavy vibrations
 

Wondering if my sagging rear springs could be contributing to this?

Re: Heavy vibrations
 

Rear ride looking lower

Re: Heavy vibrations
 

With the truck parked can you increase rpms up to 2300 and feel the vibration?
I have a similar issue but in my 65 Mustang and I have replaced everything except the engine and it is still there. I kept thinking drive line problem but it is an engine problem. Replaced harmonic balancer and flywheeldid no good. This post is irrelevant if you don’t have the vibration parked. It very well may be engine mounts.

Re: Heavy vibrations
 

Try putting a 1/8 " (thick) washer underneath the mount bolts for your carrier bearing. Yes the rear spring sag could be contributing to it too.

Having a two piece drive shaft the pinion angle, angle at the carrier bearing, on the front side of the carrier bearing, and the tail shaft all will need to cancel out. Otherwise you'll still have somewhat of a jump rope effect.

As another has mentioned, if the truck is in neutral and you bring it up to the same rpm where you feel the vibes.. does it vibrate in neutral without the drive shaft spinning?

Re: Heavy vibrations
 

Maybe a dumb question but are the u-joints correctly phased (clocked)? http://www.behlingracing.com/behling...-installation/

Re: Heavy vibrations
 

As I said before, check out your harmonic balancer and flywheel. I bought an S10 with the same problem and after messing with the driveshaft and pinion angles for a week I found out the balancer was loose.

Re: Heavy vibrations
 

Can't believe no one has suggested tires yet. Typically when things have been good and all of sudden there is a big change, tires should be considered. The relationship of the wheel tire combo is directly linear to speed as well.

Re: Heavy vibrations
 

OP indicated he had new tires mounted and balanced twice...You need to do what the factory did, hold the primary driveshaft directly inline with the transmission. They both need to be as close to level as possible. Then your pinion angle should not exceed 1* degree below what the primary shaft angle is. The 1* degree will rotate to zero under load and whatever the angle of the secondary driveshaft is, it should not exceed 3* degrees...If your experiencing the vibration sitting still in park or neutral, disregard the above...

Re: Heavy vibrations
 

Ok so I had a chance to check out the phasing of the driveshaft as mentioned. By the way thanks for all the help guys. This is my first American car, I’ve played with volkswagens all my life.... anyways, the phasing seems to be off. The yoke at the transmisssion is vertical and the ones at the rear shaft are horizontal. I have the driveshaft aligned to the registration mark that the guy who balanced it put on there. My question is it possible that the dude that balanced the shaft balanced it out of phase? I did pull the rear shaft and put all of the joints in phase but it shook pretty bad at speed. Thanks again for the help!

Re: Heavy vibrations
 

I will take a look here and see if I can spot an issuer thanks!

Re: Heavy vibrations
 

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Looking at your last picture I don't think your front yoke is in the transmission far enough. That will also cause some serious vibration. Disconnect the rear u-joint and carrier bearing bolts, slide the front yoke all the way into the trans and pull it back out 3/8 to 1/2 inch. That is where it should ride.

LockDoc