DC in the Front and STILL a vibration!!

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C

case2005

Joined
Jun 19, 2005
Threads
13
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51
First the essentials:
97' 80 series
J springs in front
OME Heavies in the rear
Front drive shaft (DC joint from a Tundra)
Slee castor plates (now)
315's Toyo MT's
4.88's (in Dec, new pinion bearings installed)
truck has about 120K on the clock

Brief History: Bought the truck last July, installed said springs in the Dec, castor correction bushings only, noticed some vibrations that sounded like they were coming from front drive shaft, checked u-joints, rear joint on front shaft had some play and was noticeably worn. Replace both u-joints on the front shaft, shaft was checked for balance etc. Installed center diff lock switch. Front shaft started to make noise again, decided it was time for DC in front shaft. Pulled a good looking DC from a tundra and had Six States(local drive line shop in SLC) add it to my old drive line, balanced again. Drove the truck with the center diff locked in rear wheel drive for a month a least. Noticed a small vibration in rear shaft (u-joints replaced). Truck sat for 3 months. Next decided to add Slee Castor plates (noticed some high speed highway issues-at >65mph)--installed those today, new shaft with DC installed and vibrations are worse than ever.

So the big Q is what do I do next? What am I missing? Do I just have a bad front drive shaft-maybe a bent yolk? I would really appreciate some help, thanks!
 
case2005 said:
So the big Q is what do I do next?
Click to expand...

Check the angles between the drive shaft and the transfer case and differential pinions on both front and rear.

For a DC shaft the front ds/pinion angle should be 0 ideally and less than about 3 degrees. For the rear, the diff and transfer case angles should be the same ideally and less than +/- 2 degrees different. The more the angles are outside this range, the more the vibration.
 
what are you using to check the angles? I have a small level but I don't know what exactly I'm going to get from that, maybe I can track down a protractor, any other simpler ways to check
 
Just read a post called GRRRRRRR is gone (https://forum.ih8mud.com/80-series-tech/73268-grrrrrrrrr-gone.html)
He noted that his rear shaft was installed "out of Phase"-- I'm kind of a new to this drive line stuff, but when I picked up my new drive shaft with the DC I asked the guy how I would know where to install the shaft on the pinion flange and the T-case now that they painted the thing. He said it doesn't matter- as long as the shaft was balanced and I didn't change the the slip yolk it just should be bolted in- none the less I tried to but it in according to the old foot print I could see on each flange.
 
I use a protractor to check my angles. I rotate the drive shaft so that one of the bearing cups is facing down. I then place a socket on that cup to use as a spacer and place the protractor on that socket. I take a reading and mine has a pointer so I mark the position. I then rotate the shaft 90* and take a reading on that cup. The difference is the operating angle of the u-joint.

On a front DC shaft you want that angle to be 0* +/- 1*.

Also, what is the over all length of that DC shaft you had made up?
 
I want to know the end of the story on this one .. it's kinda where I am headed. Subscribed.
 
Thanks for the tips on how to take the angle, I'll give it a try today. My DC shaft overall lenght is 31.5 inches with the slip yolk riding out an 1.5 inches, at least that's what I had the shop make it at. I measured it when I picked it up and that's what it was. I'll measure in on the truck when I take the angles
 
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There is no "phase" to a double cardan shaft as the DC joint makes it constant velocity. All rotational combinations of the two splined ends are equivalent.
 
case2005 said:
any idea if putting my front shaft out of phase may help
Click to expand...

This is all theorizing until you measure your angles. If your caster plates have over rotated the pinion you have 2-3* of u-joint angle at the pinion, and your DC will not like this. A DC (double cardan) shaft has two joints at the case end that cancel each other out - this means your axle end has to run very near zero degrees of angle or it will vibrate.

I had a similar issue and I ended up installing an OME bushing in the rear axle mount to raise the pinion after the caster plate install (this reduced caster as well). My Taco based DC is in driveline parlance, "dead needle", meaning perfect balance, but angles were off.

You should also remove the rear shaft if your angles look good and drive it with just the front. It is very difficult to tell whether a driveline vibe is front or rear and these aging rear shafts are going to be prone to making noise as time goes on even with new joints because the slip yokes wear.
 
Nay said:
You should also remove the rear shaft if your angles look good and drive it with just the front. It is very difficult to tell whether a driveline vibe is front or rear and these aging rear shafts are going to be prone to making noise as time goes on even with new joints because the slip yokes wear.
Click to expand...

X2 and CDL on .. ( when you are going to drive without the front DS )
 
Todays testing and results:
Crawled under again this morning, looking at stuff. Noted that the rear u-joint on the rear drive shaft had excessive play. Removed rear shaft and replaced rear u-joint (the front u-joint of that shaft I replaced in Dec). Drove the truck in front wheel drive.....YES!!! no vibrations, had the shaft balanced at the drive line shop. While there and before the rear shaft was reinstalled I had the drive line guy come and inspect my flanges on the rear diff and t-case. He notes to me that the rear flange when turning it left to right has a POSSIBLE excessive amount of backlash to it. (Side Q: how much should it have, he said it had about 1/4" to 3/8" of play). So reinstalled the rear shaft with the new u-joints. Vibrations returned. Picked up an angle finder gauge and these are my measurements (vehicle wasn't exactly on a level surface). Starting at the rear diff flange=86 degrees, rear shaft 10 degrees, rear t-case flange 82 degrees, front flange of t-case 92 degrees, front shaft 8 degrees, front diff flange 90 degrees. So how far off am I, the drive line shop guy said 3 degrees of flange angle difference is acceptable.
So where is my problem- is it the 4 degrees (86-82) difference in the rear or is it possibly the rear diff backlash. I did re-gear in Dec as well, the guy who set up the diffs for me came highly recommended. Also noticed today that the front t-case flange/bearing moved a bit (small) when shaking it up and down, but when I was in front wheel drive today on the free way and around town absolutely smooth as glass.
Bottom line-- I'm still lost.
 
landtank said:
I have no idea how to decipher what you posted. I always work with drive angles.
Click to expand...

x2

Your angles should not be 90* - that is a right angle. Get a gravity protractor and measure off the u-joints by using a socket to extend past the housing.

On a 4" lift, you should not see more than about 10* of angle in the rear driveshaft.

Chances are good that your rear shaft is more than 3* variance between the t-case and axle ends unless you have adjustable upper arms or lengthened LCA's like I did. That can cause vibes for certain, and these rear shafts will vibe with even a slight amount of slip yoke play.
 
sorry about the confusion guys, I've attached a rudimentary diagram, I hope it helps to describe my earlier post.
also to note:
Drive line shop balanced new shaft out of phase or non-parallel. Got home and looked in factory service manual-factory spec is should be in phase or parallel--maybe my problem I'm hoping. None the less I left the truck at the Drive line shop so he can do some more diagnostics (I'm going to have him switch the phasing on the shaft first of course-I hope that gets it)
compress angle diagram.webp
compressed rear1.webp
 
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Looks bad at both ends. The rear flanges should be parallel and they are 4 degrees off. On the front, the driveshaft angle is 8 degrees greater than the pinion angle. They should be directly in line or 0 degrees. If it doesn't vibrate with the rear shaft removed, the rear is a bigger problem than the front.

Since the rear shaft is a regular single U joint shaft on both ends where the flanges are supposed to be parallel, it needs to be in phase.

A DC shaft can be any phase you want and it will work the same.
 
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