GMC Truck Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
156 Posts
Discussion Starter #1
Dear Group,

I have a high speed / high frequency mild vibration. It comes in at about 70 mph and doesn't leave as speed increases, but not present below that 70 mph . Seems to be felt more in seat than in steering wheel. Had 4 wheel alignment and the tires have the Dyna Beads installed which seem to work quite well, as I have virtually no steering wheel "shake" or out of balance feel at lower speeds.

You can see my sig below for modifications. The original rear driveshaft was used, but it was fine before. The rear driveshaft has almost no angle at the rear diff pinion, but does of course have some angle at the transfer case.

Could it be lack of cancellation due to the different pinion / transfer case angles at the U joints?
Is the description compatible with a driveshaft issue?

Appreciate any of your thoughts,
Glenn
 

·
Registered
Joined
·
3,278 Posts
U-joints are probably gone. Try replacing them its a cheap job.
 

·
Registered
Joined
·
156 Posts
Discussion Starter #3
U-joints are probably gone. Try replacing them its a cheap job.
The U joints were replaced when the driveshaft was re-installed, so I would hope they're good. Only 2000 miles on them. Some WOT runs lately though.
 

·
Bayou Surface Drive, LLC
Joined
·
7,077 Posts
I would do some diagnosing before you go replacing parts. My trucks seat always did shake when going highway speeds, but no steering wheel shake. Hell it could be many things. Slightly unbalanced tires, bent rim, too much angle on u joints (get a CV at t case id you cant live with vibs). Worn u joints will probably give you the squeaking noise if they are gone and have lots of slack in them. Just dont be a parts changer until you find the problem. Find it fix it.
 

·
Registered
Joined
·
3,278 Posts
The U joints were replaced when the driveshaft was re-installed, so I would hope they're good. Only 2000 miles on them. Some WOT runs lately though.
That was not mentioned in the description so I was not sure if they where replaced. I would go to a tire and get your tires rebalanced. I always start with the easy stuff.

Just dont be a parts changer until you find the problem. Find it fix it.
Some problems like vibrations are hard to diagnose replacing u-joints is not going to break the bank. He already has new ones so I guess its not the problem.
 

·
Pat McCrotch
Joined
·
699 Posts
Could be a driveline issue. If you have a standard driveline and not a cv driveline then yours is setup incorrectly. The angle of the driveline going into the rear end should be inverse to the angle leaving the transfer case. Do a bit of research on the web about driveline angle lots of good info to be had.

Usually if you have driveline vibs at high speed and you lay on the throttle a bit harder (not enough to downshift) the vibration will change by feel and sound. There is alot of other members on here that know a great deal about driveline setup on 4x4s
 

·
Registered
Joined
·
156 Posts
Discussion Starter #7
I would do some diagnosing before you go replacing parts. My trucks seat always did shake when going highway speeds, but no steering wheel shake. Hell it could be many things. Slightly unbalanced tires, bent rim, too much angle on u joints (get a CV at t case id you cant live with vibs). Worn u joints will probably give you the squeaking noise if they are gone and have lots of slack in them. Just dont be a parts changer until you find the problem. Find it fix it.
Thanks for the comments.

When you wrote: "(get a CV at t case id you cant live with vibs)", I assume you mean that a CV driveshaft runs smooth and would correct the vibration, if in fact the rear driveshaft is the problem. Just a typo?

Thanks Again,
Glenn
 

·
Bayou Surface Drive, LLC
Joined
·
7,077 Posts
This post made me wander so i read up on driveline angles. and I have a better understanding of how to set up your angles. You need to have your t case output and your pinion output parrallel if you are running a single cardon shaft (single u jont at each end). in other words the angle fron output flange and driveshaft needs to be within 1* of the angle of the driveshaft and pinion flange.
With a CV (dual Cardon Shaft) you can point the pinion at the t case out put and not have vibes.
You have to see a roation of a drive shaft to see the variations of speed the shaft sees. the reason for running the same angle at each joint is to help cancel each others vibs out. if not you will have driveline problems
 

·
Registered
Joined
·
3,593 Posts
bad rear tires or mud caked inside the wheel, i had the same thing happen to me after about 40-45k miles on my old tires.
 

·
Registered
Joined
·
156 Posts
Discussion Starter #10
This post made me wander so i read up on driveline angles. and I have a better understanding of how to set up your angles. You need to have your t case output and your pinion output parrallel if you are running a single cardon shaft (single u jont at each end). in other words the angle fron output flange and driveshaft needs to be within 1* of the angle of the driveshaft and pinion flange.
With a CV (dual Cardon Shaft) you can point the pinion at the t case out put and not have vibes.
You have to see a roation of a drive shaft to see the variations of speed the shaft sees. the reason for running the same angle at each joint is to help cancel each others vibs out. if not you will have driveline problems

Nice explanation!
I have been wondering the very same. One source I found interesting reading on this topic was:
http://www.pirate4x4.com/tech/billavista/PR-shaft/index2.html

My setup is not correct for a standard driveshaft. Have to do some measurements and shim or get a dual cardan style driveshaft to correct this issue. Chances of it solving the vibration problem?
 

·
Registered
Joined
·
156 Posts
Discussion Starter #11
bad rear tires or mud caked inside the wheel, i had the same thing happen to me after about 40-45k miles on my old tires.

Thanks for the comments, although the tires are new and in fact I tried a diffrerent set of tires with no significant change.
The mud inside the rim causing an imbalance I have felt before, but this vibration feels different to me. As well, the dynamic balancing with the beads should compensate for the mud issue. They (Dyna Beads) have done well to compensate for snow buildup in the rims these past couple months. Exited from wheeling in the snow and drove home with no out-of-balance issues. When I got home there was still snow chunks located in the rims. Typically snow chunks such as these would cause a vibration/imblance at road speeds.

Thanks Again,
Glenn
 

·
Registered
Joined
·
424 Posts
There is a sleve(bearing) in the tail shaft of the trans that was wore out on my old 89 Silverado that caused the same thing. Grab the driveshaft and see if there is any play at the tail shaft of the trans. Had it replaced and the problem was fixed.
 

·
NCOR
Joined
·
8,449 Posts
Just shim the rear pinion to be correct for the t-case output. You have plenty of wheelbase so the angle on the joints shouldn't be an issue in terms of vibes. Shim the pinion so its 1-2* down from parallel to the t-case output to account for wrap.

Ive got 8"s of lift and a shorter rear shaft than yours(Im using a 2 peice so the spans are shorter) with no CV's and aside from some vibe from launch attributable to wrap Im vibe free to 75mph.
 
1 - 13 of 13 Posts
Top