98 379 suspension height

On a standard air leaf the distance from the bottom of frame to bottom of air spring support will not be the same for all and will affect driveline angle.

 

Try 30-32 inches bottom of frame to ground. I don't know what it should be but I worked on one and that's where it was.

 

I try to set it so that, viewed from the side, the interaxle driveshaft lines up straight with the rear axle's pinion shaft. The interaxle driveshaft is already at an angle between the front and rear axles when viewed from above, too much angle when viewed from the side will exceed the u-joint's design limitations and induce vibration.

 

http://supermiller.com/pdf/fsb1496.pdf

Here you go, straight from Peterbilt

 

Use the chart that Boardhauler posted. Measuring from the frame to the ground to compare to a different truck is not a good way to do it unless you're sure it's the same suspension and tire size. Top of the frame compared to the tire does not matter, that changes with tire size & suspension type.

 

Pretty sure bottom of frame to bottom air bag mount should average between the front and back At 11 1/2 " always been good for my trucks