Ol’ Blue my ’71 LS powered offroad truck has been giving me some bad driveshaft vibrations over 50 mph while decelerating. Looking into it further, I discovered that my pinion angle needed adjusting. Read more to see how I fixed it.

Lately on the highway, I have been noticing that I can hear the gears chattering in my NP205 transfer case while off the gas and slowing down on the highway. It is not really noticeable at less than 50mph and it isn’t a vibration that I can feel.

So I did some research online and found quite a few people saying that the gear chatter in the NP205 is due to driveshaft vibration. After thinking about it for a while, I realized that I had never actually checked the angles on my rear driveshaft.

I found this picture on TheRangerStation.com that explains the issue I was having in an easy graphic.

This picture shows the different driveline angles and what is acceptable.

So I went out and measured my driveshaft by using a dial type angle finder. I found that my transmission output was sloping down by 3 degrees and my pinion was angled up by 11 degrees. Whoops. This is exactly where my vibration was coming from. To get equal and opposing angles and make the u-joints happy, I was going to need to take out 8 degrees from the pinion angle (angle it further down).

I started out with a couple of old 1″ lift blocks that I had laying around for multiple years. Of course I could have gone out and bought some, but in DIY fashion I wanted to make them myself.

Some old 1″ thick 2.5″ wide lift blocks that I had laying around.

I could try to cut them myself, but we have a family friend with a mill in his basement. So I had him help me out by cutting an 8 degree angle on them. Thanks Joe!!!!!

1″ lift blocks with an 8* angle cut in them.

After they got cut to 8*, I lost the center hole for the leaf spring center pin to fit into, so I needed to drill a new one.

Starting with a small bit and stepping up in size.

My final hole size was 3/4″ but I have oversized center pins. Your hole will have to be big enough to accomodate the head of the bolt or pin that holds your leaf springs together.

There are two different ways to install these. One is the method described above where there is a pin on the block that fits into the leaf spring mount then has a recess for the leaf spring center pin. The other method which I ended up using, was to just have one hole all the way through the shim, then buy a longer center pin and actually bolt the shim to the leaf spring pack. I forgot to grab a picture but my version 2 looked like this except instead of the nice relief for the bolt head, I just used a grinder so it would sit flat:

If you buy these shims, they typically come in 2 degree increments. See the links below for some examples:
2.5″ 2 Degree Leaf Spring Shim – Pair
2.5″ 4 Degree Leaf Spring Shim – Pair
2.5″ 6 Degree Leaf Spring Shim – Pair

I drilled mine in a Small Drill Press, but you could easily do it with a hand drill and vice, or buy one of the shims in the links above.

Here is a before shot of what my springs and perches looked like before the shims.

As a side note, I ‘could’ have dropped the axle, spent 30+ minutes cutting the perches off with a grinder and welded them back on with the correct angle on the pinion. I didn’t choose to do it this way because 1. it would have been a lot more work and 2. I would have been locked in at the new angle where with the shims, if I need to change the angle a couple of degrees at a later date I can.

Removed my U-bolts with one of my home made sockets that I keep laying around. It is extra deep so I don’t have to do the last bit of tightening with a wrench.

A picture of the shim installed.

Lowering the pinion angle pulled the slip yoke out of the transmission a little further. The general rule of thumb here is to have about 1.5″ of slip showing.

As with the picture above, one thing you will have to keep in mind when adjusting pinion angle is accommodating for the slip yoke. When you point the pinion up the driveshaft will travel further into the slip yoke and when pointing the pinion further down it will pull out some. You just want to make sure that you don’t make it so it bottoms out or extends so far that it can slip out and pogo stick your vehicle on the freeway.

Pic showing the new pinion angle. It is not pointed up quite as far as it was. (my mistake when I was originally building the rear suspension).

For more reading, I found a couple of good articles that explain this issue more in depth.
The Ranger Station – Pinion Angles

The Ranger Station – U-Joints

I finally got to take Ol’ Blue on the highway yesterday and I no longer get driveshaft vibrations or transfer case gear chatter at highway speeds. So if you have problems with driveshaft vibrations on your vehicle, maybe leaf spring shims are a solution for you.