Driveline Vibration
 

C20 stock ride height, 4.10 31.65" high tires 7004r trans. I have a vibration that comes on at about 55 and blurs the rear view mirror. At about 70 the speed of the vibration is higher and not shaking the mirror. Also a droning is noticed.

2 piece drive shaft rebuilt and balanced by a local shop. Did not shop vibration.

Installed the 7004r trans had driveshaft shortened and balanced no change

New Tires, balanced and then rebalanced with a road force machine no help

installed pinion shims to adjust angle as recommended by shop. slightly better.

New brake drums no change

Today, I put the axle on jack stands and ran to 55 still there. I removed wheels and drums, no change. reclocked the 2 piece drive shaft a couple of times no change. Then I left the rear part of the drive shaft off and smooth as can be. It is either in the rear driveshaft portion or the rear end. (dana 60 full floater)

any ideas?

Re: Driveline Vibration
 

When did it start? When the OD transmission was installed?

Re: Driveline Vibration
 

You made it sound like the transmission came after the vibration. My hunch says it's worn pinion bearing. You say shimming reduced it some. My mind went to the pinion bearing even before reading about the shimming. The droning also would support my hunch. The whole line is balanced now, so pinion bearing again

Re: Driveline Vibration
 

Before as far as I can remember. Previously I had a 2004r and before it TH350. It always has had a vibration, but it is worse now

Re: Driveline Vibration
 

Thats what I'm starting to think also. No apparent play in the pinion yoke but something is wrong

Re: Driveline Vibration
 

I agree. You have eliminated everything except for the rear end.

Tom

Re: Driveline Vibration
 

I agree, it is time to inspect the differential.
Bearings can, and do, fail without going loose.
It also could be the ring gear bearings which wouldn't show in a pinion inspection.
I would pull the differential cover and look for evidence of a partial failure.
It should be fairly obvious, with metal in the bottom, if it is indeed the Dana 60's bearings.
BTW; You did an excellent job of eliminating the various vibration sources.

Cheers.

Re: Driveline Vibration
 

I think you guys might be right. I thought I was crazy but it seemed as if the vibration was less when cold just starting out and if I drove some distance 50 miles or so on the hwy it would be worse. Actually when thinking about it kinda makes sense. The diff oil is thicker when cold giving the bearings and gears more cushion. As it heats up the oil gets thinner having less cushion.

Hopefully, I'm not overthinking it.

My plan is to take it in and have the diff rebuilt adding posi. I do all my own work, but have to concede on working on a diff as I don't really have the tools and parts source to tackle it.

Re: Driveline Vibration
 

Have you checked drive line angle?

Re: Driveline Vibration
 

Yes and adjusted it in a little closer with a 2 degree shim.

Re: Driveline Vibration
 

A incorrect differential angle would not likely produce the symptoms mentioned.

Re: Driveline Vibration
 

that's what I found, didn't really change anything.

Re: Driveline Vibration
 

How is the condition of the driveshaft hanger bearing? If the rubber is worn it will cause a vibration.

Re: Driveline Vibration
 

Was rebuilt by the driveline shop.

Re: Driveline Vibration
 

Your symptoms sound similar to what we dealt with a few months ago.
Watch & really listen to this video. It's more than just pinion angle, but angles at both ends & overall angle of shaft itself too.
https://www.youtube.com/watch?v=SH2VIoWOQ0E
Hope this helps!

Re: Driveline Vibration
 

Experiencing the same symptoms in my 72 C20. It has a 09' 4.8L with 4L60E trans and 3.73 rear end. Driveshaft is 1 piece and balanced several times.

I haven't worked on a rear end - I would expect that the gears would have to be reset after replacing the pinion bearings?

Re: Driveline Vibration
 

I went through the bad vibe blues when I started driving my Burban. It had what I believed to be 106k miles at the time. Over several months I chased the vibrations.

New exhaust helped.

A new 2 piece drive shaft with a billet carrier bearing and a sliding joint in the rear axle and corrected U-joint angles helped.

Having the rear axle rebuilt with all new bearings and gears finally cured all of the vibrations.

It's likely that any truck with excess of 100k miles will need similar attention. Once these trucks became old and had little resale value, maintenance like oil changes became unimportant.

Good luck with your search and keep us posted on your findings.

Re: Driveline Vibration
 

Others may do it different but this is my experience.
I typically replace the bearings and reuse the same shims.
Then I check the gear pattern before calling it good.
The bearings are so close in dimensions, no matter the manufacture, it almost always works out. If you have to change the gear set it's a different ball game.

The bad news is it takes a significant amount of tools to get the bearings off the pinion. Some experience helps. Getting the preload is another PITA. Typically few have a torque wrench that measures in inch pounds. 15 inch pounds it a typical value. My torque wrench maxes out at 30 inch pounds. It can be done other ways but it's not fun without the proper tools.
Cheers.

Re: Driveline Vibration
 

Pretty much the same conclusion I have come to. Thats why I've decided to take it in and let the experts take care of it. Trying to decide if while it is apart if I want to add positraction or not. Would save some $ to keep it open. I don't go off road, or race, but am wondering if wet weather (yes I drive it daily) 4.10 gears 2500 stall/7004r with a fairly strong 350 is not a good combination for non posi.

Re: Driveline Vibration
 

My stock hp 350/350 with 3.08 open gears spins the tires at times no matter how little throttle I gave it, in the rain... if that helps at all. Tires are nearly 10 inches wide

Re: Driveline Vibration
 

Do it now and you will forget about the price soon. If you don't you will be kicking your own A** forever. :)
May save a little $ on the install as the old bearings will not have to be removed from the used carrier.
A side benefit is the right rear tire will last longer.
On the 3/4T there are at least two different differentials. Depending on the springs.
You may want to check the style and pricing on the Differential you have.
Unsure, but the Eaton could be spendy if you can find a posi carrier.
Others will have to chime in on the feasibility.

Re: Driveline Vibration
 

Hey Terry, FWIW, I had my 3.08s swapped to 3.42s and added posi when my 12-bolt was rebuilt. I like my setup with the 700R4 and 3.42 gears, although if you're on the interstate a lot I can see keeping the 3.08s. I think I'm pulling around 2000RPM at 65-70MPH, so I lost some top end, but the local driving is more fun.

Re: Driveline Vibration
 

Yes I'm going to stay with the 4.10 gears. With the OD the hwy RPM is not an issue and like you say, great bottom end. I'm a bit over 2K with my setup at around 65. I'm running a fairly tall tire, 265-75-16. I'm going to go with posi as I don't want to later wish I had. Basically everything except the actual axles will be new. I replaced the wheel bearings not long ago, so I know that those are good. Been quoted roughly $1400 with new ring and pinion, posi, new bearings and install for my Dana 60 full floating rear. I think its not a bad price given when I look up the cost of the parts themselves.

Re: Driveline Vibration
 

good advice. I have a Dana 60 full floater with 30 spline axles. Will have it all redone.

Re: Driveline Vibration
 

With a 700R4 a 4.1 is a monster stump puller gear. A 3.7 or even a 3.5 type ratio is still stout on the low end and will lower the revs at speed. TH350 and TH400 are both right at 2.5 first gear and of course direct in high. A 700R4 is 3.06 in first and .7 in OD. So effectively with a TH350 or TH400 you are 10.25:1 in first and 4.1:1 in high overall driveline ratio. With a 700R4 and 4.1 you are 12.6:1 in first and 2.87 in high. Same calculation for 3.7 rear gear 700R4 is 11.32:1 and 2.59:1. Same calculation for 3.5 rear gear 700R4 is 10.7:1 and 2.45:1. with a 3.5 and 700R4 you still have more first gear than the TH350/TH400 with 4.1 had and still drop your revs at speed about 40%. Just some thoughts.