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Mod #69: Shock Absorbers

Posted By ModMyRV On January 31, 2009 @ 12:19 pm In featured, suspension | 9 Comments

Shock absorbers don’t really absorb shock, they dampen it. Why is this important for you to know? To improve ride quality, or in the case of a towable RV, the “white knuckle” factor induced by trailer bounce and sway, it is necessary to understand a little about the dynamics a shock absorber attempts to control. This mod discusses both ride dynamics and issues associated with it, and how you can mod your RV to drastically improve your driving and/or towing experience.

Mod Difficulty:

Simply put, a shock absorber’s sole purpose is to dampen the compression and rebound of any suspension system by controlling the speed at which a suspension cycles. Without them, your RV would continue to bounce up and down until the kinetic energy is finally dissipated from the suspension’s springs (e.g. leaf springs, coil springs, torsion bar, etc.). Now let’s think about the law of conservation of energy. With this law in mind, shocks will perform two functions. The first function is to slow the suspension’s cycling of compressing or rebounding. Secondly, since energy can’t be destroyed, the shock transforms the kinetic energy into heat as it dampens the “bouncing” of the springs. That’s it. That’s what a shock does.

So why is this important? The majority of towable RVs don’t come from the factory with shock absorbers! And while class A, B, and C motorhomes do have shocks, they are often times barely adequate to control the suspension, causing wandering and excessive side-to-side motion on uneven surfaces.

To install shock absorbers on a towable RV, a retrofit kit is generally needed, although some towables already have the frame and shackle tabs necessary. A retrofit kit contains bracketry and hardware necessary to easily install the shocks. These kits use a plate that mounts to the bottom of the leaf spring shackles and has a tab for the bottom of the shock to mount to. The top mount for the shock attaches to the frame. It is often necessary to drill a hole in the frame in order to bolt the top shock mount to. This sounds scary to do but there is generally enough frame material that the hole drilled won’t weaken the frame any significant amount.

For torsion type axles, like the Dexter brand, the retrofit kits are a little different. Since there are no shackles, you must either replace the torsion arm link (from the axle housing to the spindle) with one that has a lower shock mount, or have a tab welded to the torsion arm link. The upper mount can either be drilled through the frame or an additional mounting tab will need to be welded to the frame. Much depends on your particular axle arrangement, though most torsion axle setups are generally the same.

Motorhomes are a little different. Since they already come equipped with shock absorbers, replacing them is all that is necessary. This is a mod you can usually tackle yourself as all that is generally involved is, using basic hand tools, to unbolt the shocks from their mounts and replace them using the reverse order used during removal. There may be some bolt corrosion to deal with but a little penetrating fluid sprayed on a half hour or so before bolt removal will make things much easier. If you have a motorhome that has struts (like a Sprinter) instead of independent springs and shocks, you should have a qualified suspension professional do the job. Special tools are required to compress the strut assembly in order to remove and replace the shock cartridge.

TipWhen fitting a towable RV with shocks using a retrofit kit, you will have to ensure you know how long of a shock you need beforehand as the upper mount point can vary from trailer to trailer. A close guestimate is to measure from the lower shackle plate to the middle of the frame rail. If you opt for the kit that includes shocks, make sure this measurement is within the working range of the shocks supplied with the kit.
TipIn addition to replacing shocks to improve ride characteristics of a motorhome, there are several other mods that can be done to help as well, such as sway bars, urethane bushing replacement, and even air suspension. But these are mods for another time. Stay tuned!

You can source parts for this mod from these links:

RV Shock Absorbers
http://www.monroeheavyduty.com/products/rv_trailer_shocks.asp
http://www.konirv.com/

Towable RV Shock Absorber Retrofit Kit
http://www.shockwarehouse.com/site/mon_retrokit.cfm


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