Pinion angle after lift

[riverfever]

After lifting an XJ, which way will the pinion rotate...up or down? I ask b/c on mine, it rotated up. I noticed under acceleration that the pinion will rotate upwards as well...further off setting the centerlines of t case and diff. and making vibes more pronounced. I'm still getting a local guy arguing with me that the pinion should have rotated down after the lift and that under acceleration the pinion will rotate down. Then he wants to argue that my shims are in backwards. I finally had him look while I pulled away so he could watch the axle rotate pinion up. If I flip the damn shims, it makes the angle worse. He says somethings wrong with the suspension. Can anyone offer anything? I have searched and Yucca Man steered me to the TW Driveline 101 site but it doesn't answer my question.

 

[Yucca-Man]

How did you do the lift? What size is it, and what method? (Springs, AAL, shackles?)

The pinion will normally rotate up as you accelerate; that's why when you have an SYE and CV driveshaft it's recommended that you keep the pinion about 1-2 degrees below the axle centerline.

What kinds of angles do you have now? What size shims?

 

[riverfever]

The 3" Rusty's lift was accomplished with full spring packs. The stock shackles were used.

Angles as of now are:

Slope of the transfer case output shaft=4*

Slope of the driveshaft=15*

Slope of the differential centerline=3-4*

After I installed my lift, I had bad vibes and I played with any and all combinations involving the driveline to minimize vibes. T case drop (1"), 6* shims by themselves and w/ the t case drop, 3* shims with and without t case drop. I then flipped the shims the other way after arguing with this local guy that said I had them in wrong. Vibes were worse. With the above angles and 3* shims installed with the fat partion to the front, I have the least amount of vibes. I know that my driveshaft slope is right on the maximum as far as whats acceptable. The vibes are not horrible by any means. I just got back from a trip to Colorado and probably have about 3000-4000 miles on the driveshaft u joints. The one closest to the t case is now bad. I am ordering a SYE and CV shaft next week. I know I'll have to reconfigure everything after that is installed. The operating angles of my u joints are within acceptable ranges when compared to each other.

 

[xjbubba]

Generally, my experience lifting an XJ with rear springs or blocks is that the diff angle only changes if the amount of lift to the front is not exactly the same as the rear. To the extent the front lift is not equal, you change the angle of the frame relative to the ground. This results in a downward angle of the diff, if the rear is raised higher than the front (the rear spring pirch of the rear leaf pack is now higher than its front pirch). If you then raise the front of the truck an equal amount, the diff angle, relative to ground and to the transfer case angle, should then again be equal to what they were; however, the transfer case is now higher than it was relative to the diff, so the drive shaft angle is now greater than before the lift. So whether your diff angle rotates up or down depends on the new relative hights of the front/rear compared to where they were before you lifted them. To see this, make a drawing of your drive-triain, then raise the rear and look at the affect on all parts.
As long as the transfer case-to-drive shaft angle is equal to the diff-to-drive shaft angle (using single u-joints at both ends of the drive shaft) then technically no problems should be encountered. But. An allowance should be included for the fact that the diff will rotate upward under accelleration approximately 1 to 1.5*.
Also, at higher lifts the joint angles become extereme and can mechanically bind at full droop, or cause the shaft to pull out of the transfer case. I didn't experience that problem until I went to approximately 4.5 inches of lift--I had to increase the length of the shaft and had to "clearance" the transfer case u-joint ( I beleive you can use a YJ front slip joint to gain u-joint clearance). Below 4" of lift, I don't think a CV joint set-up is required to have acceptable service life or vibration-free operation.
Youre current shaft-to-yoke angles appear good, accept I would reduce the rear diff to 2 to 3 * to account for the upward rotation of the diff during acceleration. And of course you know to set up your diff angle to arround 1 to 1.5 degrees when you install the CV shaft.
I would recommend a Tom Woods CV shaft. He's very knowledgeable regarding shafts and angles and is very amenable to discussing your needs.
Roger

 

[RCP Phx]

Generally, my experience lifting an XJ with rear springs or blocks is that the diff angle only changes if the amount of lift to the front is not exactly the same as the rear. To the extent the front lift is not equal, you change the angle of the frame relative to the ground. This results in a downward angle of the diff, if the rear is raised higher than the front (the rear spring pirch of the rear leaf pack is now higher than its front pirch). If you then raise the front of the truck an equal amount, the diff angle, relative to ground and to the transfer case angle, should then again be equal to what they were; however, the transfer case is now higher than it was relative to the diff, so the drive shaft angle is now greater than before the lift. So whether your diff angle rotates up or down depends on the new relative hights of the front/rear compared to where they were before you lifted them. To see this, make a drawing of your drive-triain, then raise the rear and look at the affect on all parts.Roger

SPOBI,your not even close!

 

[riverfever]

I don't really know poop about poop but I'm gonna guess that:
1. After lifting any XJ, the pinion will rotate up. The same way it rotates when under acceleration. Now...how much it go's up is entirely dependent upon the situation (what kit, the individual XJ, etc). If I were to take the lift off mine now and order another one from Rusty it could be different. Maybe it doesn't sit as high in the back and this will effect pinion angle.

2. For me to look at a picture of Yucca Mans shims and say they are in backwards without knowing more about the specifics is inaccurate. For his particular situation, he may have needed the pinion to come down a hair. Is this right? I've just seen guys, on here even, make that statement after seeing a pic and not knowing anything about what the working angles are on that particular vehicle.

I'm not trying to start sh!t here. I'm not looking for answers to my driveline vibes as I think I have them ironed out and will hopefully eliminate all of them with a SYE/CV. I'm just trying to better understand the geometry of this thing and 4x4's in general.

 

[Yucca-Man]

1. After lifting any XJ, the pinion will rotate up. The same way it rotates when under acceleration. Now...how much it go's up is entirely dependent upon the situation (what kit, the individual XJ, etc).

That's why I asked about your lift early on. Long shackles will point the pinion up more than new springs will, and taller blocks will help promote spring wrap, pointing the pinion even higher. The springs themselves will make a minor difference on the pinion angle, but different manufacurers may have different placement of the centerpin or springpad angle.

If I were to take the lift off mine now and order another one from Rusty it could be different.

Probably not; see the above comment about the different makers though.

2. For me to look at a picture of Yucca Mans shims and say they are in backwards without knowing more about the specifics is inaccurate. For his particular situation, he may have needed the pinion to come down a hair.

Again, for a spring-over situation, putting the fat part of the shim to the rear, with the shim between the spring and the axle will point the pinion up. Looks like I don't have any clear pics of mine so I'll break out the Paint program shortly.

 

[riverfever]

Thanks for the info. Yucca. It was helpful. I didn't know that if I went with a longer shackle in the future to get a little more height, it would effect pinion angle.


So...in your case, with the shims, your goal was to raise the pinion. In mine, I needed to lower it a bit. I would like to see pics of your rig if you don't mind. Just curious. I'm still trying to figure out how you needed to raise pinion when mine went pretty high with the lift. Would the fact that you run a D44 vs. my 8.25 account for some of the difference?


The geometry on these (and I guess all 4x4's) is pretty wild. I don't think it's too horrible to figure out if you're patient and know how to research a bit. I have learned so much with this vehicle. The lift has been on for 6 months now but I just started thinking about the driveline again the other night.

 

[MaXJohnson]

There's no substitute for measuring the angles

angle finders are cheap, cheap, cheap ...

 

[riverfever]

The angles were measured long ago. I posted what the angles were. I know the importance of measuring. That's not what this thread was really about. Thanks for your .02.

 

[xjjeepthing]

Having read this i now fell more dumb then before i started reading. I m thinking of changing my lift a bit my BDS came with a 2 1/2" AAL and a 5/8 steel block i was considering removing the block and and adding a 1" lift shackle and installing a 3/4 spacer on my front 3" lift coils thinking the shackle might be better for my pinion angle then the block now im confussed.
LOL any help

 

[xjbubba]

Adding shackels will result in a rear lift approximately equal to 1/2 of the additional length of the shackel;i.e: adding 1 inch longer shackels will result in approximately 1/2 inch additional lift, and will cause the rear pinion to angle upwards.
As Yucca-man said above, adding springs has little affect on pinion angle unless the spring's center pin position or spring pad angle has been changed. Adding or removing a lift block should not affect pinion angle either.