Drive shaft angle

[Bobbles]

Hey out there
I have just fitted some 4.8 hilux diffs to my sierra and it drives with a hell of a vibration. The drive shaft angle has a side ways agnle (because the hilux diff center is not offset) and a down angle so im assuming its this. I heard of moving the transfer case but does any one know whats involved or if there is another way?
Thanks

[gman79au]

Ive put a hilux axles in my jimny and at the start there was a vibration but ive positioned the diff so both front and rear uni's travel at the same angle and now it runs smoother than when i bought the jimny new! they need to be if one uni has more of an angle than the other than the uni with the biggest angle is going to cause vibrations.

[MightyMouse]

As its not exactly a fully Sierra question, perhaps I can offer some limited
advice. GWagenSteve could probably also assist.

From my research it matters that the tailshaft angles are similar at each
uni. Due to the nature of uni's they actually vary their velocity as they
rotate. If the uni axis are in line and the angles similar these variations
tend to cancel out - but if the angles are different or joints misalligned
then all manner of nasty vibrations and harmonics are generated.

So - check the angles, and make sure the yokes are alligned. You can
buy wedges to fit between the axle and spring to change the nose angle
of the diff. I think ARB sell them.

Hope this helps.

[Bobbles]

Thanks guys but i think the problem im faciing the most is the sideways angle. I dont need the wedges as i have just tacked the spring mounts on top of the diff. therefore i can rotate the diff till im happy. Thanks for your help.

[Gwagensteve]

Take this the right way, but I think you're missing the point.

The driveshaft doesn't know what up or down or side to side is, all it knows is that the angles don't match.

If the transfer case end is doing 5 degrees, then the diff end will have to do 5 degrees in the opposite direction or vibration will occur.

So, if the diff and transfer flanges are parallel but offset both sideways and up and down, you shoudln't have vibration because the velocity changes in the uni are in sync. If one angle is different to the other, the velocity changes will be out of sync and it will vibrate.

Of course, there are still limits, and the steeper your driveshaft, the more prone to vibration you will be and the shorter the life of the unis.

Does it vibrate under power, coast, or all the time?


Basically, the pinion of the rear diff should point down (yes, DOWN) a degree or so at rest because under power the diff will roll up. This is why I am asking when it vibrates worst.

you can roll the front of the transfer up a bit, this will allow you to raise the pinion a touch, but be aware it will affect the jackshaft, and this is very short and spins the fastest all the time.

If you are stock WB (SWB) and SPOA it is possible you just have far too much angle on the rear shaft If getting the diff angle spot on doesn't fox it, then lowering the car, stretching the wheelbase or using an offset rear diff are the only real fixes.

Remember too that for a uni, 2-3 degrees is a comfortable angle for long life and low vibration. Beyond that, vibration goes up and life is reduced. This is not much angle. A stock sierra runs almost no angle on the rear driveshaft at all.

Steve.

[gman79au]

boobles even if you tailshaft angles are the same both ends if one of your uni's is dry or tight in one or both the axis it will cause vibration too some times just a grease will fix this but it depends how bad it is.

Just another thought

[lay80n]

+1 on what Steve and Mighty Mouse have said. Also, is your driveshaft correctly phased, it may of come apart when you removed it, and be a spline out? As Steve said, driveshafts are rotational, so as long as the angle at each uni is the same, and the angles are not excessive, the uni's should cancel out each others acceleration and deceleration phase.

Layto....

[muppet_man67]

Just a question for everyone. would CV type drive shafts not fix the vibration? would there be other issues down the track for not fixing the angles?

[lay80n]

Just a question for everyone. would CV type drive shafts not fix the vibration? would there be other issues down the track for not fixing the angles?

Not in this case. A CV is often used in one end of the shaft, and then you point the other uni straight (no opperating angle at stationary ride height, if you get what im saying). But, with a zook on lux diffs pointing uni's straight is impossible,as the rear output from the shaft is offset the the RHS and the diff pinion is centred. So unless you change the drivelin to something with a centred output, you will always have an angle in the rear shaft. If you had only one uni in the shaft, it would accel and decel each rotation, with no other uni to cancel this out, vibration would happen.



Layto....

[muppet_man67]

cant you put a CV at both ends?

[MightyMouse]

CV's at both ends work - after all that is what many 4WD's have and
front wheel drive cars all have ( as far as I know... ).

Its just a matter of fitting them. Also the CV would not need to be as large
as a front wheel CV as it has the diff working after it so the torque
requirement is significantly lower.

[Toecutta]

boobles even if you tailshaft angles are the same both ends if one of your uni's is dry or tight in one or both the axis it will cause vibration too some times just a grease will fix this but it depends how bad it is.

Just another thought

I would check this as I had a vitara that was fine until I lifted it ,because the uni was worn in to a certain angle, I put in a new uni and it fixed it straight away.

My 2cents.