driveline angle question - and practical limits

Hi,

I've taken some measurements of the rear driveshaft

An angle meter places on ... reads

Transfercase output yolk 9 degrees
Driveshaft 10 degrees
Pinon yolk 12.5 degrees

I am having some trouble truly interpreting these numbers. As I read them, it would suggest the front u-joint is running at 1 degree and the rear at 2.5 ? And with torque on them, the rear would actually be about 4.5 (adding 2 degrees)? Wouldn't that mean that the rear pinion should be reduced by 3.5 degrees to 9 degrees? Or 5 degrees to 7.5?

I am wondering if the pinion is "too high"? The higher you turn up the pinion, the less oil you get in there and the less ability there is properly lubricate the pinion bearings. What is the practical limit for a 8.25 axle?

The transfer case drop will be replaced by a SYE and the rear axle reshimmed as necessary. Here I'm looking for some knowledge and education about what I'm starting with.

Tonight I removed the 1.5" transfer case drop.

Transfer case output at yolk changed to 5 degrees
Driveshaft angle increased to 13
Pinion remains at 12.5 (expected)

I take this to mean front u-joint is now running at 8 degrees and rear is 0.5 or 2.5 under torque. But I still think the rear is the "wrong way". In other words I think the driveshaft drops down from a pinion, like the angle is positive instead of negative. Next I'm going to remove the shims under the leafs and take another measurement.

Start by reading this:

http://www.4xshaft.com/driveline101.asp

Without an SYE, you need the angle of the pinion to match the angle of the drivetrain so that the motion of the u-joints cancel each other out.

With a CV shaft, you're going to want the pinion pointed at about 1-2º below the t-case output, so that when on the gas the pinion wraps up and points at the t-case.

Thanks I did read that page twice.

My understanding is that with the transfer case drop, the pinion was set up too high and should have been around 7 degrees (to achieve this, I would lower the pinion 5.5 degrees). But then need to realize that lowering the pinion affects the driveshaft angle.

I believe with either style driveshaft it should be about 2 degrees lower to allow for spring wrap and the pinions tendency to rotate upward.

Right now I'm 27" u-joint ear to u-joint ear, or 35" from transfer case oil slinger to u-joint ear. With the SYE/double cardan setup, I'll probably be about 33" u-joint ear to ear or about 20% longer which should reduce the driveshaft angle.

I also saw that there are many aftermarket covers with higher drain plugs and Dana even sells ones for "high pinion" applications. I've read a lot of people just shimming and throwing in spacers under the transfer case without seeming to be concerned about pinion lubrication.

md21722 said:

But then need to realize that lowering the pinion affects the driveshaft angle.

Click to expand...

This statement makes me think you didn't read.

If your drivetrain is set to 7 degrees, and your pinion is rotated up to say 5 degrees (leaving 2 degrees for wrap depending on how spanked your springs are) then the angle on the u-joints will be identical under load and will cancel each other out.

The angle of the driveshaft doesn't matter, unless you're maxing out the angle of the yokes or losing the slip yoke out the back of the t-case.

As I understand it, driveshaft should be less than 15 degrees, at least for day to day use.

If I set the pinion to 7, then I'd be around 9 under load matching the front.

With a SYE, driveshaft and pinion are the match points and the transfer case double cardan doesn't really matter, as long as it's within operating spec.

I think my confusion was that my pinion is higher than it should be whereas in many cases it needs to be raised higher.

Tonight I removed the shims in the leaf springs. Turns out they were 2.5 degree shims. I almost think they put them on opposite the way that would have made the angles right.

Without the shims

Transfer case output at yolk still 5 degrees (expected)
Driveshaft angle increased from 13 to 13.5
Pinion angle decreased to 10 degrees

So the operating angles of the u-joints are 8.5 front and 3.5 rear.

A 7 degree shim to lower the pinion would get me at equal operating angles, but would leave me with u-joints running at 8.5 degrees when 3 degrees is preferred.

Two questions:

1. What is the effect on pinion angle when you have extended shackles? One of the P.O.'s did the lift kit by using shackles 2X as long as stock (6" vs 3"). If I take them out, I'm also changing the ride height, so my results wouldn't be that meaningful.

2. Does anyone know what the pinion would be on vehicle at stock height with a 8.25 ? The only way I can find out is to ask or put the 8.25 under my 01 XJ which has a stock suspension.

Thanks for helping me learn.

I'm beyond confused. Go take a picture of your setup.

How much lift are you running? What rear axle are you running? Did you put new spring perches on it at all?

The u-joints shouldn't be your limiting factor, since normally it's the amount of slip yoke engaging the t-case output.

You'll most likely need a combination of t-case drop and shimming the rear axle to get the angles in check.

The best scenario is getting an SYE in there with a XJ front driveshaft (double cardan joint at the t-case) and pointing the pinion 1-2º below the t-case output.

Set your lift height before you mess around with figuring out angles. Get an sye, point rear pinion 1-2* below the rear yoke of tcase.

Sorry for the confusion. I have never messed around with driveshaft angles before, so before I install my SYE and double cardan driveshaft I was doing some measurements as I removed the transfer case drop and axle shims that were on the Jeep when I bought it. I took measurements with nothing changed, after I removed the transfer case drop, and then after I removed the shims under the leaf springs. I haven't moved the spring perches. Sometimes go slow and take extra steps to learn more along the way.

I understand it's confusing the first time you do it, but all for nought if you do t set lift height first. Go ahead and do your sye and measure for DS length. You can drive in fwd until you get it done. Once sye is in, you can meausre the angles and then figure out what degree shim you need.

Yep, that's what I plan on doing. If my estimate is correct, I won't need any shims as long as I leave the extended shackles in because they cause the pinion to rotate up. Soon enough I'm going to replace the springs and I'll need to reshim at that point.

maybe this'll help - - For non-sye drivelines.