In regards to a rough trailer ride
It appears that the OP is referring to bounce in the trailer and not necessarily in the tow vehicle so that is where I will address my comments. I’m unclear as to whether the OP is towing a 5th wheel or a travel trailer but my comments will apply to both but be less effective given the application. Years ago I was using a GMC ¾ ton Suburban for towing a relatively light 7900 lb travel trailer I was experiencing what I termed a porpoising effect. The Suburban had a 7 leaf spring pack and was very stiff unloaded but compliant when weight was added. Actual tow ratings were below trailer GVW so I was ok. The very first change I made to the TV was the installation of Bilstein shock absorbers. In my opinion they are the finest made and dramatically improved the ride quality under all conditions. Stock shocks are typically junk, even when new unless they have factory upgrades. They were installed within the first 5000 miles on the odometer. Secondly, I added a shock absorber kit to all four of the trailer wheels. Dampening the axle articulation on the TV and trailer cured this issue and the ride comfort on any surface was greatly improved as well.
I will now add my comments on the effectiveness of leaf springs as a suitable suspension for any trailer. I think that leaf springs are a very poor way to locate axles, especially on a tandem axle trailer. Just look at the axles as they twist when jack knifing a trailer into a tight parking spot? The axles and their mounting brackets scream in pain as they try to tear themselves from the coach. If the axles deflect that much during the stresses encountered in tight slow cornering how well do they locate the axles at 60 mph under compression and rebound and higher speed cornering? Unless you have the desire to make wholesale suspension design changes, there are only mods that may lessen the evils of poor suspension design. I made the improvements on my first travel trailer that I mentioned with satisfactory results with the understanding that I was dealing with cheap junk to begin with and a pretty low expectation for performance. I probably put 50k miles on that trailer and it towed pretty comfortably.
When I purchased the current 5th wheel, I ran the existing suspension about 5k miles before I could no longer stand the really crappy ride. Yes, it towed far better than the travel trailer but still had leaf springs (with correct track and CRE 3000 equalizers) and electric drum brakes. I decided to make a serious axle/brake, tire/wheel upgrade for safety and comfort. Now, my coach that used to have 4400lb leaf spring axles and 12’’ electric “dumb” brakes and 15x6’’ wheels with 225/70 Maypop radial ST tires is now equipped with 7k Dexter Torsion axles de rated to 5300 lb, 13’’ vented disc rotors and 4 piston fixed calipers, 17x9’’ wheels using 245/75 17’’ LT E rated tires. The tow vehicle wheels are also 17x9’’ on the same stock sized 265/70 tires that the truck is spec’d for. Tow vehicle and trailer wheels match…This combination has been in service for about 4 yrs and 25k miles. There is no comparison to anything I have towed as far as braking, stability, and comfort. I understand it is a lot more than most are willing to change but I like the challenge and execution of the assembly. The tow vehicle is a GMC 2500 HD with many mods that make it acceptable, those again include Bilstein shocks and Air Lift 7500 XL air bags with wireless remote system. The air bags are for levelling only and I used the higher rated bags so that I could run them at a lower pressure and still retain a compliant ride. At max GVW I use 27 psi of pressure in the bags to obtain a level ride attitude.
