What degree shim do I need - I have all the angles measured

[DaveD912]

You guys are probably tired of hearing from me... so, just one last question. In an attempt to fix my DS vibes without an SYE, I measured my DS angles.

I have a 231 t-case, stock DS, 8.25 rear.

The T-Case points down at 6 degrees - measured from the valve cover.
The pinion points up at 9.5 degrees - measured from the circles on either side of the cover.
The shaft is at 17 degrees, but I don't think that plays into things.

I think I need a 3 degree shim to point the pinion down more - putting the fat side of the wedge towards the rear bumper. Is that right?

 

[jeepme]

You will most likely only find a 2.5* shim which will work. If you need to lower the pinion the fat side of the shim will be facing the front of the Jeep.

 

[DaffyXJ]

Been awhile since I looked this up in the FSM, but:
The operating angle of the ujoints needs to be 1 to 3 degrees. The more the operating angle the more the likelyhood of vibrations and the shorter the operating life of the U-joint.
Operating angle is measured by C-A minus C-B where:
A is the transfer case output angle
B is the rear axle input angle
C is the Driveshaft angle
These are measured (with the drive shaft installed, and the truck level) from the Ujoint end caps at the tcase, rear yoke and at either end of the drive shaft, (Same on both ends).
You might want to re measure at the ujoint locations vs. the places you did, but with the numbers you have.
Front operating angle of 11 degrees
Rear operating angle of 13.5 degrees
Ujoint operating angle of 3.5 degrees. 3 degree shims will put the ujoints (Based on the measurment points you used, which I think yo still want to remeasure from the ujoint end caps) at less than 1 degree operating angle which would be optimal.
As to which way to rotate the pinion, need to know if the 9.5 degrees is + or -.
Re measure and recalculate.
Check out http://www.4xshaft.com/index.html for more info.

Derik

 

[DaveD912]

You will most likely only find a 2.5* shim which will work. If you need to lower the pinion the fat side of the shim will be facing the front of the Jeep.

You're right, thank you, this is why I asked

 

[RCP Phx]

Id say start with a 4* so the pinion will be slightly under(for torque wrap).

 

[DaveD912]

Id say start with a 4* so the pinion will be slightly under(for torque wrap).

Good point, I just ordered a 4* steel shim. I'll post back when I put them on. I'd be nice to solve this with a $30 shim instead of an SYE and DS.

 

[vetteboy]

The operating angle of the ujoints needs to be 1 to 3 degrees.
Ujoint operating angle of 3.5 degrees. 3 degree shims will put the ujoints (Based on the measurment points you used, which I think yo still want to remeasure from the ujoint end caps) at less than 1 degree operating angle which would be optimal.

1-3 degrees? Most manufactures spec 7* as maximum allowable from the factory, which is based on a worst-case situation. You can go as high as 10-15 before you'll really start to notice anything.

It's true that life expectancy of the u-joint is based on that 3* operating angle, typically somewhere in the neighborhood of 5,000 hours for a standard joint, and it goes down proportionately from there as angle increases. Which means at a 10-degree angle, you probably won't notice any vibes yet, but the life expectancy goes down to 1500 hours. At 3 hours a day driving (about my commute), every day, this works out to be about a year and a half - before any noticeable wear occurs.

Shimming the rear only adjusts the pinion angle, not the t-case angle. You don't want to have the effective angle at the pinion be 0 while having a single joint at the t-case. In that situation (which I think the OP properly diagnosed) you want the pinion and t-case output to be parallel, splitting the difference in angle evenly between the two joints. This cancels out any vibrations as much as possible without going to a CV/double-cardan setup.

 

[DaveD912]

Just for the record, I re-measured at the yokes, as DaffyXJ suggested, and the numbers came out to be the same. In a few days (waiting for shims) I'll know if I can use shims instead of an SYE.

 

[Rocketman]

The 4* shim should get your angles within a working plane. You want your TC yoke and the rear diff yoke on the same parallel planes. The rear is better if it points no more than 2* down from the plane to correct for wrap. A 4* will give you about a 1.5* wrap adjustment. It should come out pretty nice.

Watch how much of your yoke is exposed as when you flex drastically, it CAN fall out. TC's for some reason, don't like running without fluid in them!

I ran almost 2 years with a stock DS and 6* shims no problem. Needed the TC drop though to correct binding in the joint. After a SYE and a new DS, I was able to remove the drop and reverse the 6* shim to get my angles perfect for my rig. It just happened to work out that way for me with my lift and rig. Your mileage may vary!

 

[DaveD912]

Just a follow-up... the shims are installed and the yokes are now parallel. The noise at 34 mph is gone Thanks everyone!