Pinion Angle vs Slip Yoke Angle

It's been a while since my last post here but I have been a part time lurker and now I have come upon a problem I'm am having a little trouble with the best solution. I have done research and found two answers and would like to hear from other people's experience.

Jeep specs: 8.25 axle, 242 transfer case, aw4 transmission, 3.5" RE suspension.

I had zero vibrations when I installed the lift with the original Dana 35 axle. I blew out the LSD and had lots of metal shavings in the diffential so I decided to just upgrade to an 8.25. When I installed the 8.25 I kept the drive shaft from the Dana 35 as it was a half inch longer and I figured this would keep more of the slip yoke more engaged especially with the differential further away from the lift. This all worked well for over a year still with zero vibrations.

I lost the rear universal joint on the highway and the driveshaft and differential yoke wear both damaged. I have replaced the yoke and installed the spare driveshaft that came with the 8.25. I get vibrations at around 25-30 mph now.

I think the first step to try to remedy the problem is to correct the pinion angle, I will consider and SYE if that does not work. I have measured the following:

Drive Shaft: 18*
TCase Yoke: 5*
Pinion Yoke: 9*

Do I adjust the pinion down 4* to match the Yokes? This seems logical in the sense that the u joints will move in equal and opposite positions and create balance. This would have the joints operating at 13*.

Do I adjust the pinion up 9* to match the drive shaft? This seem logical in the sense that the u joint at the pinion will have minimal movement and reduce vibrations at this joint as it operates at 0*.

What solutions have you guys used. I have researched and found information on both scenarios.

Thanks for any input.

Your pinion is too high. With a slip yoke it should be about 2 degrees less than the yoke at the tcase. If you had an sye the pinion would need to be 2 degrees less than the driveshaft.

DansGreyMj said:

Your pinion is too high. With a slip yoke it should be about 2 degrees less than the yoke at the tcase. If you had an sye the pinion would need to be 2 degrees less than the driveshaft.

Click to expand...

Thanks for the input.

So with the slip yoke I need a 6* shim down to bring the pinion angle to 3*. If I get the SYE I would need a 7* shim up to bring the pinion angle to 16*. This means a 6-7* shim should work and with an SYE I would just flip the shim.

Where are you getting the 2* difference? Is this a factor spec? Is this a small enough delta to allow rotational harmony while still placing the force from the axle movement to the slip yoke with out u joint bind?

The two degrees is to allow for pinion rotation under acceleration. It's information I found doing research years ago and I've never had any vibes with any of the axles I've ever setup, with and without an SYE.

Before that though, how are you measuring the angles?.
The driveshaft angle and pinion angle are adjusted to the t-case yoke angle.
The best way to bring the driveshaft and pinion angle into adjustment is to install new perches, but shims will work too.
You do want the pinion angle to be slightly lower than the driveshaft angle for "axle wrap".

Transpoquick said:

Before that though, how are you measuring the angles?.
The driveshaft angle and pinion angle are adjusted to the t-case yoke angle.
The best way to bring the driveshaft and pinion angle into adjustment is to install new perches, but shims will work too.
You do want the pinion angle to be slightly lower than the driveshaft angle for "axle wrap".

Click to expand...

I have a protractor with a float that points downward and tells you the degrees off from level. I rotated the yokes until the flat portion was on the bottom and then placed the straight edge of my tool on the yoke. So the slip yoke is 5* below flat and the pinion yoke is 9* above flat.

If you have a 2000 and 3.5 inches of lift, a 1 inch transfer case drop may help, but the correct long term solution is an SYE.

Measure the pinion yoke angle by using the machined surface the diff cover bolts onto. It is 90* square to the pinion.

The two round machined flats on either side of the diff. cover are perpendicular to the jeep pinion.
W/ the jeep at ride height put a digital angle finder like harbor freight: 95998 on the flat. I use a small 5" square w/ a bubble in the handle to make sure the gauge is level.
Then put it on the driveshaft, subtract and that's your angle's.
Even that angle gauge is +/- 3 degree, closer than anything non digital imo.
After you adjust the angles, to whatever d-shaft set-up, you can figure out if your driveshaft is long enough.

Btw if the d-shaft is 18 degree and the pinion is 9 degree, that means your pinion is 9 degree lower than the driveshaft angle. That's probably why your having issues, pinion needs to be rotated up, which makes sense for 3.5" of lift.
And I didn't read the previous post closely enough. The surface under the diff. cover and the machined flats at either side are at the same angle as the pinion shaft.
Heavy duty SYE from tom woods for 242j is a great idea. I bought and installed one on my xj, have not used it yet though.

According to Tom Woods custom drive shafts ( http://www.customdriveshafts.com/ ) when using a regular 2 u-joint shaft, the angles at each u-joint should be the same.

The rear end should only be rotated to align with the drive shaft when a CV shaft is used.

9 degree's is to much.
op could rotate the pinion to lessen the angle.
The diagram above doesn't give actual angles because of all the variables when setting up a driveshaft.
Cv style still should be 1.5 degree lower at the pinion then the d-shaft angle.
According to tom woods instruction's for installing one.

What if he had a six inch lift and the pinion angle was, lets say 6 degree and so was the output on the t-case. I guess you could make a driveshaft to connect the two, but the angle's would be horrible.