Can I gain ground clearance by shiming the flip axle

Is this a RGN trailer? Do you not have air bags??

 

Sounds like you jumped in the deep end before learning to swim.
Rear ride height is controlled with air bags, shim the axle too much and you will put all the weight on it, not a good thing.

 

Can you take pics of the trailer, the rgn (in particular the dog ones) and the flip? Blot out your numbers if needed.

 

3 places to shim.
1.on the neck.
2.at the transition if a modular deck.
3.the flip axle.

The first 2 gain you ground clearance.
Shimming the flip will only increase or decrease the weight on the flip.

 

There is something wrong with your trailer if you have 1/2 inch of ground clearance after taking on 40,000 lbs.

 

Have you checked the weight?
I have had them say it was 40k and truck couldn’t lift trailer off the ground.