Pinion angle help (read: lotsa vibration)

[Osmosisfrank]

Yes, the lowers are all the way in. I could try cutting them down a bit to give me a little more room to shorten, but then my rear diff gets pulled under even further and would look silly.
Got a quote today. If I disconnect the top links and rotate the pumpkin, get the right angle, take the measurement on how much longer they need to be, I can get them sleeved for around $50 each. If I have adjusttable links made out of them, $110 to $120 each. I like the idea of adjustability, because if I'm a little bit off on my measurement, then I may be pushing the LCA's out and then I'm back to the whole "rear end is not centered" thing again. I'm not O.C.D., but that would annoy the snot outta me.
(Starting to get a real good idea about that J.E.E.P. acronym...):doh:

 

[SeeJay]

Wow if the pictures of his pinion are off....no wonder my jeep has such a bad vibe. I have searched (Setting Pinion Angle) on this site and found no result. Is there a link I can go read and figure out how to do it?

 

[lazyxj]

Wow if the pictures of his pinion are off....no wonder my jeep has such a bad vibe. I have searched (Setting Pinion Angle) on this site and found no result. Is there a link I can go read and figure out how to do it?

 

[lil_red_wagon]

its simple if you have a normal slip yoke rear drive shaft with single u-joints on each end then you will need equal but opposite angles on the out put shaft comin out of the transfer case and the pinion angle on the rear end.

on the other hand

if you have a double cardon joint like ones that go with sye's then you need the pinion inline (pointing at) to 2* lower than than the out put shaft on the transfer case

the reason behind this is that

with one u-joint on both ends and the angles the drive shaft speeds up and slows down 2 times with every rotation. if the angles arent the same the shaft will speed up and slow down at differant speeds on each end and cause vibration

with a double cardon joint on one end that is what its for to do the speed up and slow down right there in the joint and it needs the other end to spin true if the pinion isnt pointed directly at the shaft (upto 2* below to keep it greased properly) then you will have it speedin up and slowing down on thepinion end and it will fight the cardon joint causing vibration.

sorry for the long post

 

[lazyxj]

Wow if the pictures of his pinion are off....no wonder my jeep has such a bad vibe. I have searched (Setting Pinion Angle) on this site and found no result. Is there a link I can go read and figure out how to do it?

Some how my earlier response didn't get posted so here it is.

Check the links on Tom Wood's website technical page.
http://www.4xshaft.com/index.html

Ideally, the front pinion should be as straight as possible, while maintaining 5 degrees or more of caster.
The FMS calls for 5.25-8.5 degrees of caster, it also states that the pinion shaft angle has priority over the caster angle.

The rear shaft pinion angle will vary depending if your XJ has a stock drive shaft and slip yoke or if an SYE and CV drive shaft has been installed.

 

[kastein]

with a double cardon joint on one end that is what its for to do the speed up and slow down right there in the joint and it needs the other end to spin true if the pinion isnt pointed directly at the shaft (upto 2* below to keep it greased properly) then you will have it speedin up and slowing down on thepinion end and it will fight the cardon joint causing vibration.

Rest of your post was pretty much spot on, this is wrong though - you keep it 2 degrees below the shaft so that under torque the pinion will rise due to spring wrap and result in a nearly-zero U-joint angle. That's why in this case he should preset to nearly zero U-joint angle, because he's got a coil conversion installed so there isn't much, if any, spring wrap/pinion rise.

 

[lil_red_wagon]

oh ok i understand. that part i was explained to wrong then

 

[SleeperXJ]

You need degree shims, your pinion is pointed way to low. -B

I've got to agree with boom, pinion angle is way low. It should match the drive shaft angle maybe 1* lower when sitting on the ground.

 

[lpennock]

Rest of your post was pretty much spot on, this is wrong though - you keep it 2 degrees below the shaft so that under torque the pinion will rise due to spring wrap and result in a nearly-zero U-joint angle. That's why in this case he should preset to nearly zero U-joint angle, because he's got a coil conversion installed so there isn't much, if any, spring wrap/pinion rise.

It also has to do with body squat or rise under acceleration so even thought the axle doesn't wrap you may want a little static angle to compensate for body rise.

 

[kastein]

As far as I know body squat/rise is the same animal as spring wrap essentially (pinion rises, wraps springs slightly till the spring stiffness stops letting it wrap, then starts making the body rise.) The angle relative to the ground does not matter on either the axle or the body, just the body to axle angle.

 

[lpennock]

As far as I know body squat/rise is the same animal as spring wrap essentially (pinion rises, wraps springs slightly till the spring stiffness stops letting it wrap, then starts making the body rise.) The angle relative to the ground does not matter on either the axle or the body, just the body to axle angle.

Actually spring wrap is a different animal but does also affect the squat/rise. In spring wrap the axle actually rotates even if the relationship to the body doesn't change. This results in the pinion turning upward under acceleration. Depending on the springs and the amount of acceleration it is possible to get spring wrap and not change the relationship of the axle to the body; however, once you pass a certain about of wrap the axle relationship will change because the spring wrap effectively shortens the spring pack and the spring tension also acts as a lever between the axle and the body.

With a 3 or 4 link system the axle doesn't rotate as much; however, there is some wrap do to bushing compression on arms if you are running rubber or poly bushings. In addition, as the axle moves through the range of motion the axle may rotate some because the arch of the lower and upper control arms isn't identical. The "solid" mounting of these systems actually result in more body rise as the control arms act as a lever to try and push the axle from the body. This is what causes drag cars to appear to lift up and level out. So when you put the tendency for the axle to move away from the body and the unequal control arm arcs together you get a shift of pinion angle. It is usually pretty small but it does exist and should be accounted for when setting the pinion angle.

Now with all that said +-2 degrees probably makes no difference in the system so setting a 3-4 link system to 0 degrees is probably fine; however, 1 degree down is probably better if the system has any bushings in it.

 

[chpmnsws6]

Sorry...taken with a cell phone.

The t-case is stock, NP242. No shims or drop kits. The slip yoke eliminator on the rear: I don't really know. I bought the driveshaft and SYE from Teraflex. Installed, $350. That kinda hurt. I think I could have done it myself for cheaper getting a Tom Woods unit.

Your rear end needs shimmed pretty badly.

 

[Osmosisfrank]

UPDATE:
I had Ben Hanks (of Ben Hanks Racing in SLC) add 1.25" of front-to-back length on my upper link setup. Then, I cut 1/2" off of my lower control arms. Pinion angle to driveline angle is now -0.5* (pinion down) and the vibrations are gone. Also had Teraflex press in a new u-joint, as the old one (only two months old and 200 miles on it) was shot.
Tonight I'll reinstall the front driveshaft and look at that angle. I think I'm going to have to rotate the housing forward to get the pinion angle close to 0*, which will wipe out my caster, but from what I've been hearing, pinion angle is more important than caster. I can't afford $700 to have my knuckles rotated, even though that's the right thing to do. I missed out on a Warn hub setup, but there again, a tad pricey. So, maybe next spring I can afford to get it done right.
Thanks again everybody for the help on getting this problem straightened out (pun intended!).

 

[lpennock]

UPDATE:

Tonight I'll reinstall the front driveshaft and look at that angle. I think I'm going to have to rotate the housing forward to get the pinion angle close to 0*, which will wipe out my caster, but from what I've been hearing, pinion angle is more important than caster. I can't afford $700 to have my knuckles rotated, even though that's the right thing to do. I missed out on a Warn hub setup, but there again, a tad pricey. So, maybe next spring I can afford to get it done right.
Thanks again everybody for the help on getting this problem straightened out (pun intended!).

Just make sure you don't get the caster too low or you won't be able to keep it going straight down the road. I've run as much as 5 degree u-joint angle without significant vibration but staying a 3 degrees or less is better. You really don't want to get your caster below 2-3 degrees or it will become a real hand full.

Also if you have adjustable upper and lower arms you can push your axle further forward to give so a better ujoint angle. Just means you need to trim the fender a little more in front. Everything is a trade off.