Ok Geometry wizards. I want to make sure my thought process is correct...

My Jeep is parked in my dirveway which has a 1 degree downward slope away from the garage (measured on the ground right below the steering knuckle). The front of the Jeep is at the garage door.

Castor reads 5.5 degrees (measured under the steering knuckle).

I am using a simple angle finder for measurements.

Question - Does the 1 degree from the driveway add to the total castor reading or subtact from the reading. Meaning, should I assume that if I was on level ground the castor would be 6.5 (add 1 degree) or 4.5 (subtract 1 degree).

This will determine my canging control arm lengths this afternoon!

 

????

 

No. It does not.

 

The degree of the floor will affect your reading.

 

Hmmmm....conflicting information?

 

Since your simple angle finder is basically a glorified plumb bob and is working off of gravity of course the angle of the driveway effects it. Think about how it would effect it if the driveway was 10 degrees instead of one degree and you will have figured out your answer.

 

Here is the info I received from another forum member that has a significant level of alignment experience. But some input from others still has me a little confused. I'll let him claim his write up-but just in case he wants to remain anonymous...

The driveway angle does not matter. The ground the Jeep is sitting on has absolutely nothing to do with the caster angle. The caster angle is the angle of the steering axis, ahen viewed from the side. If it is at straight verticle it is said to be at zero. If the top of the steering axis is tilted toward the rear of the vehicle, the caster is positive. Toward the front, it is negative. The definition of "verticle" in this instance does not indicate verticle to the "earth", as in most other instances. It refers to the vehicle. "Verticle" in alignment terms when concerning caster simply means "perpendicular to the horizontal vehicle centerline." As you can see, you could theoretically flip the Jeep upside down and that angle would not be affected.

 

While his/her explination is correct, it depends on what type of angle finder you are using. If you are using a gravity angle finder then you must take the angle the ground below the jeep is on into consideration. If you are using a fixed/manual angle finder, then you don't take it into account.

 

So if I were to follow the thought that the driveway will affect the reading, then my current reading of 5.5 is actually 4.5 and I probably don't want to go any further than that.

I still have a little bit of vibration between 45-55 that I am thinking might be the new front JE Reel Driveshaft. My rear is set up even DS to Pinion. If my castor was actually 6.5, I might have tried to decrease it by shortening my front lowers. I may at this point just leave it and see what happens. If I do adjust it, I probably can only go one more turn before I would go past 4.0 degrees

 

Just to be clear, if your driveway is 1 degree up, then yes, your 5.5 is really 4.5.

With my 4" TF lift, I'm at 5.5 and I'm going to take mine up to 6.5. WOL recommended 6-7 for the 4", but TF says 3.5. I think you gotta just keep playing with it until you find it.

I'm not sure I agree with the recommendation of a few degrees below the pinion for the rear DS. I was told to set it up even, which is what I did, and it drives great.