We have two suspension issues here... truck and trailer.
First the truck
For the springs
If the truck sags too much when stationary, it's a matter of springs, not shocks. If the truck springs need shoring up, I like the idea of add-on air springs
. Like Pete, I think it is better to avoid using the shock mounting points to carry the load of the air spring, but it can work fine. The Firestone applications list shows a Coil-Rite
air bag as the appropriate fit for the rear of the Mitsubishi Montero Sport, 1999 to 2004. AS Pete said, this goes inside a coil spring, so if the list is right the Montero must have coil springs, not leaf springs. If so, this is exactly the setup (okay, a different size bag, but the same brand and design) as I use in my Sienna minivan.
There is also an Air-Lift brand of the same type of thing. The Timbren site shows both of those brands as well as their own, but the image of theirs is not of the right type of spring.
Denise, what year is the Montero? It looks like 1998 and earlier have leaf springs, and thus use a different style of air spring, as shown by Timbren's Air Lift part.
If you have any questions about the Coil-Rite product, I suggest calling their tech support line: I did and found them quite helpful.
If it is too bouncy on long bumps and rough on sharp ones in operation, that's shocks, not springs, so I agree something new and described as "heavy duty shock" is called for.
How about doing the shocks first, then deciding if the springs need help? As long as you are not considering air shocks, the shock and spring decisions are separate, and good new shocks certainly couldn't hurt.
The photo is of the trailer
shocks. The top mount is on a frame bracket, but the bottom is hard to see in the photo. The suspension looks like a typical rubber torsion axle
- the hub is on a short (maybe 6") arm which pivots in the end of the tube which goes across the frame. I think
there is an arm going straight down from the pivot point (and hidden by the shock in the photo) to the bottom of the shock: if this is the case, then when a bump pushes the wheel up, the shock is compressed, and any shock absorber of the right size which is okay operating tilted like that will be fine (some shocks really want to be vertical).
The most likely problem finding a shock will be getting one short enough. The Monroe heavy-duty "Gas Magnum RV
" shocks which I put on my Boler
- the ones intended for use with the mounting kit
- were the only ones from that company which were short enough to fit. They have the same mounting style as the MKP shocks, so the same ones I used might be the right choice.
Some trailer axle
shocks are pulled
in bumps (a reverse to the normal action), and thus should have different internal valving... that's why it matters how it is connected.