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Project Vehicross Part 8: Pinion Angle 101

by David Zipf

 

It’s been awhile since we’ve done anything with our funky Isuzu project. There’s a simple reason for that: I was planning to replace it with a Mazdaspeed 3 (in 2016) and have a fun, practical, and incognito hatchback to replace the fun, tough, and weird Isuzu. Due to a series of unfortunate events (some relating to a lazy previous owner, and some relating to unfortunate shortcomings in Mazda’s quality), we decided to offload our 3 and keep the Isuzu. That meant dealing with some of the issues we’d been ignoring for months while we fussed with the Mazda.

The biggest problem we’ve been ignoring is our driveshaft. See, back when we lifted our VX with an OME Lift Kit we mentioned that our driveshaft started making odd noises. After doing some poking around, both under the truck, and through the brains of some truck people, we realized the problem was due to our driveline angle. In a rear or four wheel drive application, the driveshaft must cover some vertical distance to meet with the pinion gear in the axle. When Isuzu designed our suspension, they set the driveshaft at a certain length and a certain angle to prevent undesirable harmonics. These harmonics will cause unwanted noise and, if severe enough, can even cause failures in the driveshaft, rear end, or the transmission or transfer case.  

When a live axle rises and falls throughout its motion range, it does not do so linearly- it actually moves in an arc. At factory ride height, the driveline angles cancel each other out, but when you lift the suspension, the pinion angle increases and the difference causes a vibration, which one can hear inside the passenger compartment. Determining which angle is the issue is fairly straightforward. If the vibrations come under acceleration, the transfer case/transmission angle is too steep. If the noises come under deceleration, the pinion angle is too steep. Our noises always came under coasting situations (side note, if you hear noise under both conditions, but only at certain speeds, you have a driveshaft imbalance).

It should be noted that the front end of the VehiCross does not have these problems. Not only does the front driveshaft use CVs, but because the front end is independently sprung, the front diff does not move when we lift the front. The front axles are put under more strain as they operate at more of an angle, but since they are not causing us problems, we are only working on the rear end.

Fixing the mismatched driveshaft angles can be done with some adjustable suspension links. Independent4X supplies off-road parts for a number of Japanese imports and has a very nice Isuzu section. I4X is one of the few places you can get aftermarket Isuzu parts to build your Trooper, VehiCross, or Amigo into a Jeep shaming rig. They make their own heavy duty turnbuckle style lower links for just such an emergency, and they also offer options of lower links, upper link, or all three in a kit. We decided to start with the lower links only and see if that did the job.

 

These are our Independent4X lower links. I4X offers the upper link as well, but we passed on it for now. We would have loved to grab an adjustable Panhard rod as well, but they does not offer one, which is a bit disappointing. Technically, these links are for the Trooper, but the VehiCross is built off the Trooper’s Japan-only short-wheelbase chassis (which uses the same suspension), so these fit the VX perfectly.  
 
The links are beefy. They are made from 2 inch, 0.25” wall DOM steel tube with fat 3” rod ends. These suckers are heavy, weighing a solid 20 lbs each, at least double the factory thin wall links. The super thick walls are designed to soak up hits from rocks and ledges. These links can be used as rock sliders if you’re planning to do some serious off-roading in your Isuzu.
 
The rod ends are gigantic, yet they fit the factory Isuzu brackets with no trouble. The bearings are sealed and have high articulation for maximum suspension flex. They can also be rebuilt and serviced- perfect for those who will dunk their Isuzu in mud or water.
 
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Comments
Dusty Duster
Dusty Dusterlink
Thursday, December 07, 2017 1:42 PM
Had to do the same thing when we lowered the grey Project Mustang 5.0, but we corrected the pinion angle with an adjustable upper control arm instead!
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