389 ride height again...?

You need to set it to factory specs, unless it's at factory specs already.

The more air that's in the bag, the stiffer the ride is going to be.

If the bag sits higher on its base compared to before, there's too much air in the bag, which means the height isn't correct.

Call the Pete Stealership with your VIN# and ask them what the ride height should be and where to measure it from.

 

The correct spec of 8.5"axle center to bottom of frame. This is the laden spec. Unladen is 8.75". Any other measurement is false. The best way to do this without the proper gauge is measure axle center to ground and measure frame to ground and subtract the two measurements. Dont guess because an inch off can make a world of difference. Make sure your on level ground when measuring. Dump the bags to cycle and back up to full height and recheck again after adjusting. Leave the engine running to make sure air pressure is maintained during the adjustment process. I prefer to take the measurement between the drives.

 

I would leave it where it drives with no viabration. The whole idea of ride heights is to get the diff angles correct so there is minimal harmonic vibrations caused by the u-joints.
The listed height spec is more of a guide of where to start at. To do it correctly, driveline angles need to be taken and punched into a corresponding program such as Eatons Driveline Angle Analyzer. Low air leaf would typically be looking for angles like 1.6 front diff, 6 interaxle, 11 rear axle.

I normally would adjust a truck with a tape measure first, then confirm/ fine tune by running the angles.
Leave it at the height that doesnt vibrate. Longer life for the u joints and syncro.

 

While I agree the temporary thing to do would be to adjust the where the vibration is minimal to prevent further damage to components. If the ride height is set to spec and a vibration is present, something is wrong. Start measuring and find out what's off to fix it right.

 

Best answer. Factory spec does not mean correct. Factory kicks out drivelines at wrong angles all the time and by putting it to factory spec can cause an issue. Wish quality control would be taken more seriously! Trial and error, patience and tape measure.

 

Factory ride height spec will get you close. You have to go off the driveline angle and set your ride height to that. If you have an iPhone they have a wonderful little level in them works awesome for checking shaft angles. My ‘05 has AG380 and the ride height specs are the same. I have to set mine to 8-3/4” loaded to get my shaft angles correct. That suspension is 6 different kinds of a pia for holding adjustment too. I’m at that one steady.