Rotated Knuckles - Toyota Axle Housing

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Author: Scott Wilson June 2000

My Pinion Angle Problem
Editor's Note

This is an extreme modification and should only be done by qualified persons. The author assumes no responsibility should you choose to implement the ideas presented here on your own vehicle.

My poor pinion angle

After doing a solid axle conversion on my 1988 4Runner, I was left with a terrible pinion angle. The pinion was pointed about 10-degrees below my transfer case output. As you can see in the picture, even when I had the right wheel compressed, the pinion angle was still bad. I was using a CV-type drive shaft, so my pinion angle was FAR from ideal. Click here to learn more about the different types of drive shafts available, and the ideal angles for each drive shaft. The poor pinion angle created extreme vibration when the front hubs were locked, or if 4WD was engaged. Speeds above 15 mph were not possible while spinning the front shaft due to the terrible vibration caused by the front u-joint.

I also noticed while the truck was on a lift and the front axle was allowed to fully droop, that the front u-joint was binding due to the very steep angle. Between the bad vibrations and the possibility of breaking parts from the binding u-joint I sought to fix the problem. Normally shims would be the best way to adjust the pinion angle, so that is where I started.

I went to the local 4WD parts store and purchased 3-degree and 6-degree shims. At a glance I knew my pinion angle was at least 6-degrees off, so first I installed the 6-degree shims. I quickly found that I could not use these shims because they caused my drag link to contact the spring when trying to turn left. The shims rotated the entire housing, including steering components, and knuckles. The reason the steering components were now hitting the spring was because the steering components were now 6-degrees from normal, but the spring was still in its normal position.

Next I installed the 3-degree shims. With these shims I did not have the problem of the drag link hitting the spring, so I decided I would take the truck for a spin and see how the 3-degree shim changed things. I engaged the hubs to see how bad the front u-joint would vibrate, and took it for a spin. The vibration had improved slightly, but it was still not acceptable. I drove the truck for a day (hubs unlocked of course) and constantly noticed how poor the steering felt. Since the axle and everything attached to it was now 3-degrees from where it normally was, the steering geometry and wheel caster had changed. The new feel of the truck was not a comfortable one, and I quickly made time to pull the shims out again. Frustrated with my inability to easily fix my pinion angle & lack of funds, I chose to wheel the truck for nearly a year and just put up with the problem, before finally deciding how I would correct it.

I knew of three options that would correct my pinion angle, none of which I considered cheap. One option was to swap in a Toyota 8" high-pinion 3rd member, available in Land Cruiser FJ80s. These 3rd members sell for a premium, and the 4.88 reverse cut gears I would need makes the price even higher. The next option was to install a dual transfer case. A 2nd transfer case would move my transfer case outputs back around 6 inches, which would improve my front driveline angle. The cost of doing this is about $500 plus the cost to lengthen/shorten both drive shafts. While this modification also has the benefit of adding lower gear ratios, I saw it as a very expensive way to cure my pinion angle woes. If I did not already have a Marlin Crawler 4.7:1 gear set in my truck I'm sure I would have chosen dual transfer cases to fix the problem.

The last solution was to purchase a rotated axle housing, modified by an experienced shop. On a Toyota axle housing the knuckles extend into the axle housing. They are pressed in place, and then welded to the housing to prevent them from moving. A rotated housing is one in which the knuckle ends have been cut, rotated a certain number of degrees, and welded back together. Since the knuckle is never cut through, but only cut 'loose' then rotated, then welded in place again, strength is not compromised. The steering stops, shock mounts, and spring pads are also removed, and replacements are welded on at the new angle.

The reason for doing this is to get the pinion pointed upward, while leaving all steering components, wheel caster, spring pads, and shock mounts in their original plane. Rotated housings can be purchased for around $300, still not what I consider an inexpensive fix. This was the cheapest option available to me, however, after a little research I decided I was capable of performing the work myself.

By doing the work myself I could knock the price down to $35, plus many hours of my own labor. The price was definitely right, and I believed the end result would have the performance characteristics I was looking for; a perfect drive shaft angle, the same wheel caster as before, and no spring/drag link clearance issues. Follow along as I show you how I cut and rotated my housing, and tell how closely the finished product met my expectations.
The Solution to my Pinion Angle Problems
Sand blasted axle housing - mounts already removed

I had recently acquired a sand blaster, so I started by sand blasting the housing down to bare metal. This removed all grime, as well as paint, which made handling the axle much nicer. Next I had to remove all the mounts from the axle. I had a friend with a torch remove most of the mounts for me, so I only had to grind the housing smooth again. The only mount we left on the axle was the steering stabilizer mount.

Spring pads remain for reference

Upon inspection I found that the top of the knuckles (measured across the top of the knuckle bearing race) were in the same plane as the spring pads. I decided this would be 0-degrees, so I could make all of my measurements from there. For this reason I asked my friend not to entirely remove the spring pads, to leave enough material to firmly hold them in place, but little enough that I could easily remove them later. Once I had the knuckles rotated and welded, I could then remove the spring pads, create new ones, and weld them on at the same angle as the knuckles.

Factory knuckle weld Top of weld ground off

The picture on the left shows the original factory knuckle weld. Since the 3" pipe cutter I had seen had a roller as well as cutting blades I used my grinder to take the top of the weld off, to make it level with the axle housing. As it turns out the only pipe cutter available for rent was a 4" pipe cutter with 3 blades, and no rollers. It turns out I could have gotten away with not grinding the factory weld down since there was no roller.

I used a rented 4" pipe cutter Cut inside of the factory weld

Here is the pipe cutter in action. It cost me $15 to rent it for the day, but the cutting only took 15 minutes. A 3" pipe cutter would be large enough to do the job, but since the 4" model uses all blades and no rollers it might be the better choice. Extra care needs to be taken to be sure the cutting is done perpendicular to the center line of the axle. If the cut is not perpendicular, when the knuckle is rotated the knuckle will pull out of the housing slightly, increasing the distance between the knuckles. The cut should also be made just inside of the factory weld. The cut should go through the first layer (axle housing) but not through the second (knuckle).

Welded back together

Once the cut is made the knuckles are still held firmly in place (press fit at the factory), making it a little difficult to rotate them. By using two long axle shafts through the holes in the knuckles, a friend and I were able to rotate the knuckles. It was not an easy task, and one that must be very precise. Unless you have a way to hold the housing in place while you rotate both knuckles, one side must be completed (including welding) before the other side can be rotated. This is because we had to use axles through both knuckles (one as a holding force) to get enough leverage to turn one knuckle.

Using a magnetic mount protractor (the 'angle doo-hicky' is the proper garage name) I took my best guess at how many degrees I would need to rotate my pinion up for it to be aimed at the transfer case. I decided it was between 9 and 10-degrees, so I rotated the knuckles 9.5-degrees. Welding the knuckles back together was relatively easy. The pipe cutter had left a nice 'v' to lay a bead in, and the metal was very clean.
3" hole saw for spring pads Driver side spring pad

Since the knucles were done, it was now time to move on to spring pads. I wanted my new spring pads to be in the same plane as the top of the knuckles, and at the 'factory height' from the axle centerline. The passenger side spring pad is higher from the centerline than the drivers side spring pad. I made my spring pads using 3/16" wall, 2.5x2.5" box tubing. A 3" hole saw made the correct arches for the spring pad to sit on the housing. The driver side spring pad is relatively easy to make, it is symmetrical.

Spring pin hole 3/4" from center line

Side note: While I was creating new spring pads I drilled the hole for the spring center pins 3/4" back from the true center of the pad. This is one method of moving the front axle forward, and it is the cheapest method. It is common to do this to the front of Toyota mini-trucks since larger tires chew at the firewall/fender with the axle in the stock location. The center hole in the u-bolt plates must all be drilled 3/4" back to move the axle this way. My spring pins are 1.25" forward, and these holes are now 3/4" backward. My axle now sits 2" forward from the stock location.

Unsymmetrical right side pad Gusseted for strength

The passenger side spring perch is much harder to make since it sits on the side of the differential area. The perch is unsymmetrical, and takes some effort to get it to sit flush on the housing, completely level, and in the correct plane. I used my hole saw to roughly remove the material I need to, to make it sit flush on the side of the differential. Then I removed the remaining material with an angle grinder, carefully test fitting the perch until it was just right. Using an idea from Jay Kopycinski, I gusseted both of my spring perches to insure they do not bend when the forces of extreme wheeling are applied to them.

In addition to spring pads, I also had to create new shock mounts and steering stops. If I had been thinking better when the shock mounts were torched off I would have saved them. I think it would be very easy to clean the torched edge of the shock mount and reweld them to the axle. I did move my shock mount inward slightly for better tire clearance if I ever start using a wider tire, or a tire with side lugs.
Differential Guard

The new angle of the axle housing aims the thin metal differential cover down towards the ground, making it more susceptible to damage on the trail. While I was doing this work I installed a Westec differential guard to help protect the thin differential cover. Click here to find out more about the diff guard. Because the pinion bearing is now higher than it was previously, the gear oil level must also be higher to insure the bearing is properly lubricated. I chose to overfill the housing through the existing fill hole, but if necessary I could add more oil through the breather hole located on the top of the housing.

The new angle of the housing also makes fitting the passenger side u-bolts tough. Since the housing begins to get taller than 3", right near the differential, the shape of the housing dictates which direction the u-bolt wants to go. I planned to bend a u-bolt into a shape that would work well for me, but I found no amount of beating was going to get it to bend. Nothing short of a large shop press could have bent the u-bolt. I ended up using the unbent u-bolt. I started both passenger side u-bolts through the u-bolt plate, and slowly tightedned them down, coaxing (with a HEAVY hammer) the u-bolt plate over the center pin until it dropped in place. Now that the u-bolts are tightened down one of the u-bolts has a slight bow to it, but nothing to make me worry.
The Results
Two dark pictures of the near perfect pinion angle

Here you can see the pinion angle now that housing has been installed. As you can see my guess at the angle was very close, within 0.5-degrees I believe. Since the steering components and wheel caster remain in the 'stock plane,' steering feels exactly like it did before, and the drag link does not hit the spring. The true test is how well the front drive shaft likes this new angle. I thought I gave it a thorough test by driving it at 50 mph with the hubs locked and experiencing no vibrations. It turns out I accidentally gave it an even more thorough test. I forgot my hubs were locked and drove the truck on the freeway 60 miles south to Hollister Hills, at speeds up to 80 mph, and never had a clue the front shaft was spinning. It wasn't until I aired down and went to lock the hubs that I realized I had been spinning the drive shaft the entire way there. I'd say the housing did the trick!

I'm extremely pleased with the outcome of this project!

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