I have a 1999 17' Casita
SD and when I switched from 14" to 15" tires and wheels 6 or seven years ago there was a slight rubbing on the left side going over bumps. I was thinking the axle
was just not aligned properly so I designed and made a slight lift, about 1.75". When I started to align the axle
I quickly found the axle
was aligned correctly but the "egg" was not centered on the frame.
I agree with Robert, unless it's been replaced already the Dexter torque flex axle is past due. I've read that Dexter says 15-20 years and my 19 year old trailer's ride has gotten much harsher over the past five years.
As they age the rubber suspension parts harden resulting in a very hard ride.
I ordered a new axle "beam" only just week. I have about 8k miles total on my brake drums and backing plates and have a new set of Timken bearings and new seals.
Cost for the axle beam only
at a local RedNeck trailer supply was under $300 plus tax. The 3500 pound axle comes with 10 brakes