[Zukinator]

Since going SPOA, the vibration coming from the front d-shaft when running in 4wd has made 4-HI almost unusable. I know others have had similar problems and was wondering what the consensus was on the fix.

Any help would be appreciated.

 

[AZZZUKI]

Check yr timming marks, sounds like they may be out.
I had the same thing, timming was out.

 

[1339]

What Azzzuk said, but also, how much lift are you talking about? Have you checked the U-joints? Are
they greased?

 

[Nowhere]

If you have a sloppy slip joint (ha!) you can reverse the driveshaft (have the slipjoint down at the 3rd member side) if clearance allows. This has allowed me to use 4x4 high range again. Worked well for me with no adverse effects.

Definatly check the phasing between the 2 halves.. One of your u-joints may be bound, check for slop everywhere/every direction.

 

[Zukinator]

I'm fairly certain that the dots are lined up .. I'll double check though (after temps are above 19*). There was some vibration before doing the spoa but it wasn't too bad. Now it looks like the dash is going to shake loose.

My front u-joints are a couple years old. I have 4.5" +/- of lift.

 

[Zukinator]

I'll pull the shaft again and check everything.

One thing that bothers me is that I haven't even installed the d-shaft spacer in the front yet. It seems that if the vibration is due to the angle, this will make it worse when I do install it.

 

[3693]

A spacer will make the angles worse (albeit only slightly). Are your t-case and pinion driveshaft angles matched? If you tipped the pinion up when you welded on your perches, that will cause the problem you mention. On a regular driveshaft, you want the u-joint angles at each end of the driveshaft to be complimentary. People often tip up the pinion to get a decreased angle (at that end) only to find out later that they just caused a vibration problem because the t-case joint angle has lost the 'canceling-effect' of the other end. If your angles are off much, you can get vibes at speeds around 10 mph.

 

[ackerdackerly]

Zukinator:

Quite often, the vibration you describe is related to the alignment of the two halves of the driveshaft. Double-check to make sure that the yoke pieces are exactly in the same plane with each other.

The front driveshaft is pretty long, making it less prone to pinion angle vibrations. If you change the front pinion angle from the factory setup you will affect castor and make handling go bad -- like the way the front wheels wobble on a beat-up shopping cart.

 

[841]

actually if you look the t case is angled slightly back. (it isnt level) it is higher in the front so to realistically to make the pinion angle right the pinion would need to be pointed into the ground. I think in the stock form it was a trade off better angles for the short rear driveline that sees continous use, and the worse angle for the front.

my front pinion stock actually pionted at (or close to it ) the t case

I get pretty good vibes above 35-40 spoa axle pushed forward 1 in 2 in extended drive yoke + 1in spacer 4.57 gears 33 tires

 

[3693]

szki272: You are right. The stock setup isn't even technically correct, and for the reasons you state, it really can't be. I have my pinion tilted up about 5 degrees (to get the castor right) and I get vibes at a lot lower speeds. Nothing on mine is stock except the t-case though. I have just seen too many guys angle up the pinion for a "better angle" (when it technically speaking is a worse angle for a std driveshaft) and then find they have driveshaft vibration and death wobble up the wazoo. Unless you want to cut and rotate the knuclkes and get a front CV driveshaft, you are forced to compromise between castor angle, pinion clearance, and driveshaft vibration. For me, I rate their importance in that order. But depending on what you use your rig for, you might have a difference list of priorities.

 

[1339]

Something I forgot to mention was the lack of a spacer might be makeing things worse. Depending
on the wear on the splines, you might not have enogh engagement to keep the 2 halves from wobbleing.

Take a look at how much the splines are actually engaged, and se if you can shake the splined joint at all.

 

[Zukinator]

Its too cold and snowy to pull the shaft today but I decided to do another run to see if anything made sense.

Earlier I had never run over 20 mph in 4-HI. Today I pushed it up to 45 mph. After reaching 25 mph, it started to smooth out and wasn't too bad - it was actually o.k. When I slowed down it would shake really bad between 25 and 10 mph and when letting off the gas at lower speed it would make a noise (fairly loud) that didn't sound like griding but something wobbling so bad it almost sounds like grinding - if that makes any sense. Sounded more like the tcase than any part of the shaft.

When I got back, I grabbed the shaft and it seems tight but its hard to tell without taking it out.

Seems like it could be a tight joint because of the difference when increasing the speed. -- ? or maybe I need to install the spacer. The other noise almost sounds like my front output shaft might have some slop but it isn't leaking and doesn't make noise all the time. -- ?

With the hubs locked and the tcase in 2wd, its not a problem.

Thanks for the replies.

 

[676]

Ummm...

If the roads are good enough for you to be doing 45 you shouldn't need 4wd..