Double Cardan Angle Question

Hello,
I have a lifted XJ with light vibes at highway speeds. Today I replaced the axle shims, going from 4* to 6* in hopes to correct any vibes. As it turns out, the "6*" shims were a little over what they claimed to be. As it stands, I'm reading right at 15* on my pinion and 13.5* on the shaft. This places my pinion 1.5* OVER the center-line of the drive shaft....In the ideal situation I know the pinion needs to be 1-2* UNDER in the center-line of the shaft, to account to pinion rise during acceleration.

My question is, will this be detrimental to my drive-train? I don't want to order new shims and run in to the same thing again....also, I'm on a limited timeline. Other than lifting my transfer case, does anyone have an idea for possibly modifying the 6* shims to make them less aggressive (while still keeping them flat)?

Anyways, just exploring my options. Thanks for the feedback.

How much lift do you have on the xj?

I bought the OME 3.5" lift and it is closer to 4". Although the lift height shouldn't matter in this case

escout said:

Hello,
I have a lifted XJ with light vibes at highway speeds. Today I replaced the axle shims, going from 4* to 6* in hopes to correct any vibes. As it turns out, the "6*" shims were a little over what they claimed to be. As it stands, I'm reading right at 15* on my pinion and 13.5* on the shaft. This places my pinion 1.5* OVER the center-line of the drive shaft....In the ideal situation I know the pinion needs to be 1-2* UNDER in the center-line of the shaft, to account to pinion rise during acceleration.

My question is, will this be detrimental to my drive-train? I don't want to order new shims and run in to the same thing again....also, I'm on a limited timeline. Other than lifting my transfer case, does anyone have an idea for possibly modifying the 6* shims to make them less aggressive (while still keeping them flat)?

Anyways, just exploring my options. Thanks for the feedback.

Click to expand...

Lets say your 6 degree shims are actually 7*, and you went from a 4 to a "7*" and now your 1.5* over, that means that you were "perfect" with a 4* shim. Unless your 6* shim is closer to like 10 degrees, then it sounds like there is probably another issue. (driveshaft u-joints? Balanced?, try flipping 90* or 180* on the drive shaft to see if it changes anything?)

Either way, to answer your question, you would be better low than high in my opinion, at least that way if your under load, either on the road, or off road (where you'll probably have more axle wrap) you'll end up closer to "good".

If it was me, I'd toss those 4* back in.

Most people have said 1* per 1" of lift, typically a 3-4" lift needs a 4* shim. This is also dependent on how the lift is assembled, if your doing a shackle lift, it would be different. I can tell you I had OME 3.5" lift, stock shackles, and needed a 6* shim, I threw in shackle relocation brackets, and lift shackles, and gained about an 1" of lift, but due to the rotation from the shackles, I actually needed less shim, and now I'm at 4*.

Does the current "6*" set up vibrate as bad, or less?

If you don't mind a little more lift, you could probably throw in a pair of lift shackles, and swap back to the 4* shims, and you'd probably be perfect. again, this is all assuming this is the true problem, which I have a feeling it is not. Should probably ask what the angles were with the 4* shim.

I just did a calculation, based on the dimensions of the "6*" shims....Turns out they are actually between 8-8.5*.....not ideal. I confirmed this by looking at pictures of my angles with the previous shims. I haven't driven the jeep yet...I suppose that's next on the agenda. I would like to avoid more lift in the rear by using shackles, since I'm already a little higher than I want to be. That's a good point though, I didn't think about the shackles affecting the pinion.

It sounds like 4 degree shims are what you need. Driveshaft itself could be vibrating because of a problem with it or anything else in the drivetrain for that matter. I would put the 4 degree shims back in and try to isolate the problem.

Based on research and what I'm hearing, the 4 degree shims were ok, but based on looking at those previous angles and re-checking my current ones, 6 is where I need to be for that drive line to be in phase....It's incredibly frustrating buying parts that are out of spec. I'll take it out for a drive tomorrow sometime and see what the new set feels like.

escout said:

Based on research and what I'm hearing, the 4 degree shims were ok, but based on looking at those previous angles and re-checking my current ones, 6 is where I need to be for that drive line to be in phase....It's incredibly frustrating buying parts that are out of spec. I'll take it out for a drive tomorrow sometime and see what the new set feels like.

Click to expand...

I have a set of Rubicon Express 6* shims, sitting on a shelf. (RE1468 is the model #) If you google them on Amazon it says their aluminum but thats wrong, their steel. I can double check them and make sure they are a true 6* but if you want them, let me know. cover shipping and a 6 pack, and their yours.

I appreciate the offer for sure, but I ended up taking the shims that were too steep and ground them down to get the angles I needed. Currently, I'm right about 1.5 degrees below the center-line of the drive shaft at the pinion, to allow for pinion rise, as others have said. Also, my drive shaft is at 15.5 degrees. I'm still getting vibes.....Any ideas??

escout said:

I appreciate the offer for sure, but I ended up taking the shims that were too steep and ground them down to get the angles I needed. Currently, I'm right about 1.5 degrees below the center-line of the drive shaft at the pinion, to allow for pinion rise, as others have said. Also, my drive shaft is at 15.5 degrees. I'm still getting vibes.....Any ideas??

Click to expand...

I'd start with rebuilding the Driveshaft. Replace all 3 of the u-joints and rebuild or replace the centering ball, get it balanced, and toss it back in, see if it makes any difference.

Rebuilding was the key for me, mostly at least. I have the OME leafs and I'm sitting right at 4" in the rear with the 4* shims, and 3.5" in front. Still had vibes, so I rebuilt both shafts and had them balanced which is required after a rebuild. MUCH better now!! It's still not perfect, I still have some from 65-70, but my leaves are still settling in.

So, I've been messing with my angles and I seem to be getting closer to the goal. From what I've been reading, as your drive shaft approaches 15+ degrees of slope, vibration becomes inevitable. It sounds like 10 degrees is the ideal working limit.....auto manufacturers seem to avoid anything over 7 degrees. I think once I can get the pinion angle happy and the shaft closer to 10 degrees of downward slope, then my main focus will be getting shafts balanced/rebuilt, if I still have an issue. I didn't expect this issue to require so much research, but hopefully it pays off.....

Just curious....how much can I lower my t-case before the shift linkage is affected?

My next step is to put in 3 degree axle shims, drop the the t-case just a hair, and re-check. I should be darn close to 10 degrees. I'll update later this week, whenever my shims show up. Thanks for all the input thus far, I'm trying to incorporate all that I can into this.

With SYE and double cardan driveshaft then the 15 degree isn't so much a problem, you point the pinion 1-2 degrees under the driveshaft and call it good. The double cardan takes care of the angle at the transfer case. Leave the transfer case alone. When you start running worn u-joints at new angles they can complain for a while, or maybe until replaced.