Your kid took the family pickup and lifted the suspension higher than Boulder Colarado on April 20th. Now the driveshafts are too short and they vibrate like a Hello Kitty Shoulder Massager.
The truck may have had a 2 Joint shaft similar to the one below:
2 joint shafts have a limited operating angle. The following table lists the maximum rpm for given angles:
The solution is to replace the 2 joint shaft with a Constant Velocity shaft
A CV Shaft is purchased and installed, or the truck has an existing CV shaft, and the operating angles have changed. Yet, the vibrations continue. That is when a Pirate 4x4 forum search leads to a pinion angle thread. The information on the thread is an entertaining mix of facts and opinions. With all the ambiguity, there is no clear direction and you do not want your project to end up under the GhettoFab topic.
A local wheeler recently purchased a CV shaft for the exact reasons stated above. The driveline was set up at an area racing chassis shop, and the rear driveshaft was a 2 joint shaft operating at 20 degrees, causing a vibration at road speed.
A CV shaft was built and installed, and at that time, set up instructions and this diagram were communicated:
The transfer case angle can be as much as 22 degrees. The pinion angle must be less than 1.5 degree, preferably 1 degree low.
After months of questions and complaints, the vehicle was rolled into our shop.
Note: We Strongly Dislike working on other people's vehicles. Never, ever ask us to work on your vehicle!
If your vehicle rolls into our shop, we will put your picture on the internet.
The information below is information only! This is NOT a DIY instruction page!
Never attempt chassis mods without proper training and tools!
The following information is here for educational purposes for those who need direction with their project vehicles.
Note the NP231 transfer case with a slip yoke eliminator shaft.
Inspection of the setup immediately revealed the U-Joint angle out of spec.
At some point, in an attempt to fix the geometry, wedges had been placed between the leaf springs and axle. This can be helpful sometimes when troubleshooting, or determining proper setups, but it is not recommended as a permanent solution. In this case, 3 degree shims were installed where 15 to 20 degrees were needed. "I shimmed the axle like you said, and it didn't make it better."
The pinion angle is determined by the location of axle perches that are welded to the axle tubes on the rear differential. The best way to adjust the pinion angle is to remove the perches and weld them back on in the proper orientation.
Axle perches prior to removal:
The only way to remove perches without vandalizing the axle is with a thin wheel. It is a thankless job that results in abrasive wheel dust sticking to your face like glitter at a third grade girl's birthday party.
Once the welds are sliced with the thin wheels, a large chisle and hammer are used to break the perches from the axle tubes.
The perchless axle:
The axle tubes and perches must be ground free of any remaining weld before reattaching the perches.
Grind those tubes!
The old welds have been removed from the axle tubes. The perches and differential are placed on the leaf springs.
The U-bolts and plates are temporarily reinstalled. The wheels are put on the vehicle and taken off the safety stands. The pinion angle must be set with the suspension at ride height.
The pinion angle is adjusted by rotating the differential
With the pinion angle set, the perches are tack welded in place.
Note the fat-guy-yoga-shop pose.
The vehicle is then placed on safety stands, and wheels, u-bolts and plates are removed.
The perch welds are completed.
The suspension is reassembled. The u-bolts are trimmed.
Always retorque the u-bolts several times after getting back on the road.