Brake chamber issue.

Not following you on how a 24/30 would have more clearance. The spring chamber is the exact same size as a 30/30. Be a real bad idea to put a 24/30 in there, you'll lose nearly 20% of your service braking force on that axle.

 

If the problem is only with the rear axle & the front is fine perhaps it wasn't built with spring brakes on both axles? Some have spring brakes on one axle only.

 

Maybe the u-bolts were replaced and are too long

 

There are also 24 / 24 chambers but do not recall them on Pet's. Dealer can tell you with last 6 of the vin.

 

Can you pull the spring shackle bolts out, flip them over and put them back in the other direction for better clearance?