A little background, 99 4.0 has 2.5" springs and 2" spacers. I bought it like this and am trying to get rid of some vibes. I measured as per Tom Woods site.

This is the front CV(stock not double cardon) axle. The pinion is pointing up 5 degrees, the driveshaft is at 8 degrees, and the t-case is pointed up 2 degrees(sloping slightly to the rear).

I think I want to tilt the pinion back down to 0 degrees. This is the part I am not 100% on, but it would make the upper working angle at 10 degrees and the lower at 8 degrees instead if the 10 degrees and 3 degrees I have now.

I would just like to know if this makes sense and am going the right direction. Any help would be great. Thanks Jami

I'm not too farmilliar with WJ drive lines, but i do know about driveshafts and pinion angles. Does your front shaft have the cv joints at both ends of the shaft? (axel end and t-case end) If it does, you can run the pinion and shaft ant any angle, and as long as there is no bind in the joints, it wont vibrate. If its only cv at the t-case end (which is usually the case) and the axel end is a normal cardan joint, then you want yout pinion angle to be 0 degrees (or 180 degrees depending on hoe you look at it) relative to your driveshaft. Either way there should be no driveshaft angle at the pinion if you are running a cv at the t-case. That is, the pinion should point straight at the t-case output at ride height.
As soon as a cardan joint is at any angle it introduces a back and forth motion(higher and lower velocities) to the driveshaft a few times per revolution. Normally this is countered by another cardan u-joint at the other end of the shaft, but with a cv joint at the other end this shows up as vibrations. This is because a cv keeps the shaft at a constant velocity instead of trying to counter that back and forth motion.

This makes more sense if you actually look at a diagram of the driveshaft.
Why heres one now for a cv setup: (it dosent matter if you are running a double cardan cv or a rzeppa style cv, the concept is the same)

and here is one for a regular cardan setup

These were taken from tom woods website. If you call them they customer service is excellent, I'm sure they could help you fix your problem, even if you dont buy anything from them. The wont over sell you if you do buy something either. Really and excellent company.
hope that helps.

 

Thanks for the info outcast.

I have the CV joints(like a fwd car) at both ends. So what you are saying is that I would probably be better off riasing the pinion a few degrees, and treating it like a traditional Doble Cardon CV. I guess the the fact that it is CV joints and not U-joints is really confusing me now.

Maybe I will start by raising it 3 degrees(in line with the shaft). and if that doesn't work, drop it to zero.

Any other input

 

Thanks for the info outcast.

I have the CV joints(like a fwd car) at both ends. So what you are saying is that I would probably be better off riasing the pinion a few degrees, and treating it like a traditional Doble Cardon CV. I guess the the fact that it is CV joints and not U-joints is really confusing me now.

Maybe I will start by raising it 3 degrees(in line with the shaft). and if that doesn't work, drop it to zero.

Any other input

you have to be careful, since on the front end, any pinion angle change also affects your camber/caster and almost every other alignment setting. If you adjsut the pinion too much you will loose your return to center, or wear out tires too fast.

A dual cv setup like that should aperate and just about any combination of angles without vibration, unless one of the joints is going bad. Car style CV joints dont like high torque and steep angles. If your joint is bad, i'd say ditch the cv and go to a double cardan. I know on my brothers 99 we switched to a front double cardan, and it runs smooth. It was a part that chrysler carried, a whole shaft and yoke kit. It might be easier/cheaper to call tom woods and see what they can do for you though.
I got my cv rear for my cj, $300 with the "trail hazard" warranty. Pretty much no matter how bad you screw up the shaft for any reason, its replaced for free, as long as you own it. Its the warrany for someone like me who is on their 3rd rear shaft. (first tom woods shaft though, best drivesaft ever)

 

I am aware of the Caster change issuses associtated with tilting it up.

I will get a a standard U-joint shaft once the budget allows, I am just trying to get rid of the crazy harmonic Vibes.

I guess I will start with a few degrees in one direction and see if it improves.

Thanks again Outcast

 

I'm just curious, since your front driveline sounds like it should not really be casuing the vibes, have you checked the rear driveline ? I noticed you haven't mentioned it yet and was just curious why you seem to have ruled it out.

 

I'm just curious, since your front driveline sounds like it should not really be casuing the vibes, have you checked the rear driveline ? I noticed you haven't mentioned it yet and was just curious why you seem to have ruled it out.

First off, the rear angles all jive. It is within 1 degree at both ends.

Second, the vibes seem to be coming up from the front floor boards and only at faster speeds(~50 in overdrive). The vibes are harmonic and what I have found through searching all of these problems lead to the front. I am not 100% sure the rear isn't contributing, but I am pretty positive the front is not right.

 

Try taking your front DS off and driving around and see if they go away. It won't take you long to find out.

 

have you had you tires dalanced lately?

if you are in 2wd your front driveshaft will not cause vibration because nothing should be rotating up front.

now, if you are only in 4wd when you get the vibration then I would suspect it would be the pinion angle.

 

No, I haven't had them balanced. I am actually getting new ones, so we will see. I am also going to remove the shaft and see what we get. I was also under the assumption that it is still spinning since there are no manual lock outs.

 

yup... they still spin.

 

I was also under the assumption that it is still spinning since there are no manual lock outs.

sorry about that...I didn't notice that there were no lock outs on the front end of these things.

usually when you have vibs comming in at just certain speeds with a range of 5 to 10 MPH it is the tires. a good way to check with out taking it to the shop would be to rotate them yourself. move the front to the rear and see if the vibs move. also when you move an out of balance tire to the rear it should feel less harsh.