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TeeJay 12-14-2007 07:46 PM

Shock tech.
I tried to search if anyone had discussed this before and I couldn’t find anything too specific. So I did some research.

There are so many shocks out there and so many questions about how they are best used. I wanted to see what I could do for everyone on the forum with a little shocker101.

The basics are how shocks even do what they do. We all know they make it ride smoother and eliminate bounce, but how? Shocks, simply put, displace fluid through movement. This in turn causes heat conduction. Every shock out there uses the same principle, a piston moving through fluid will slow down do to high friction. On the head of this piston is a series of valves (holes) that allows only certain amounts of fluid to pass through. Bigger or more holes equals a softer ride, but at the price of traction and response time. On top of that, every shock varies based on velocity; this means that the faster it moves, the more friction it encounters and the faster it slows down as well. As a result, shock absorbers not only slow the compression and rebound of your springs, but can also reduce bounce, roll or sway, brake dive and acceleration squat to some degree.

We’ve had some talk in sections concerning stretches and lifts about angles of shocks and direction they travel in. Angle is probably the single most important thing in a shock configuration. Luckily, most of us will use the angles selected by the boys at Chrysler Design. As for the rest of you, if you’re modifying these angles, you will probably want to do more research on your own, but here’s a start. If you think of an axle as a lever you will know that there’s more control on the ends then in the middle. This is why in an ideal world we would love our shocks mounted outside the tire. It’s too bad we would look like fools. Also perfect would be a shock that lost nothing because of an improper angle. You get 100% efficiency from a perpendicular orientation. Too bad that if we do that every time our shock becomes a flex limiter. Some good rules to follow though: mount your shock as far outboard as possible, use approximately the same angle for your shock as the one your axle articulates on. The more we make this inward angle (toward the pig) the less effective our shocks become and the more crucial it becomes to upgrade to a stiffer or higher pressure shock tube. As a general rule if you need an 100psi shock it is only 100psi when it is perpendicular to your axle. At a 20* angle it is only as effective as a 90psi shock perpendicular and at 40* it’s now only as good as a 75psi shock would have been.

For a leaf sprung axle there are a few other things to consider. Namely, where are your shackles? If they’re in the rear, then your shocks should lean slightly rearward. Reason being that as your springs compress and your axle travels it uses the shackle as it’s ‘give’ point. The entire axle moves toward it. The last thing you want is your shock to be pulling away from this point, try to mimic this angle as well as the articulation angle when you are deciding on placement. Again, I cannot stress enough, if you are altering your geometry consult an expert and do some digging on your own. And don’t be afraid to learn from others mistakes.


TeeJay 12-14-2007 07:49 PM

Almost all of us have changed our travel and vehicle height (if you haven’t yet skip this, but you’ll be back) How do we figure out what shock length to use now that we’ve done this? Especially YJ’s or any leaf sprung axle. How much longer is a 2.5 inch spring with SOA conversion and a 1.5 inch revolver shackle then stock? Pencils down please. There is a much better way to do this as far as accuracy is concerned.The measurement is fairly easy. Measure the distance from the suspension bump stop to surface that it makes contact with, and add a ½" for compression of the bump stop. This measurement is your compression travel. Now measure from your upper shock mounting point, to the lower mounting point. For explanation purposes, lets say that the distance from the bump stop to the contact surface is 5.5" and we add a ½" we now have 6". Lets also say that the distance from the top mounting point of the shock to the lower mounting point is 14". Given these two measurements it is easy to see that you have a difference of 8". This 8" measurement is the length of the shock body you would need to control travel, measured from the mounting eye to the top of the shock body, and not limit suspension travel. In this situation you would actually have approximately 8" of rebound or droop travel in the shock and 6" of compression travel.

TeeJay 12-14-2007 07:50 PM

Shock types
Twin-tube shocks

A twin-tube shock is the "entry level" shock absorber if you were to compare all shock absorbers against each other. These are considerably cheaper to manufacture, but offer the least consistent dampening in comparison. Twin-tube shocks are much more likely to fade and aerate (form bubbles within the oil) with aggressive use or even just a washboard road.

Coil-Over Shocks

Coil-over shocks are fairly simple by design. A coil spring is placed over and around the shock body, adding an additional spring rate to the shock absorber. These coils can be placed over just about any type of shock absorber depending upon the manufacturer. Unless you have a specific need for these shocks, or if you plan on using this design as opposed to a leaf or coil spring suspension altogether, don’t bother. A firm gas or hydro shock will cover most of our needs.

Gas / Pressurized Shock Absorbers

The benefit to these is that gas shocks can be valved differently to offer a ride just as smooth as a twin tube shock, while still providing far superior shock-damping consistency than any regular shock on the market. What is the major difference with gas charged shocks though? In theory, they will never aerate, when this happens, the oil within a regular shock absorber gets air bubbles forced into it, forming a frothy, foamy goo. This causes the oil to flow through the valves of the piston at unpredictable rates and decrease the performance of any standard shock. We like gas/nitro shocks because they are smoother and less likely to lose traction holding power when we need it most. Nitro/gas pressurized shock absorbers are built with pressurized nitrogen inside the shock body. The pressure can range anywhere from 80 to 350 or more p.s.i. This keeps the oil from aerating because nitrogen does not mix with the shock oil, and forces the oil molecules to stay packed together much more closely, thereby all but preventing the oil from getting any air bubbles within.

Mono-Tube (Single Wall) Shock Absorbers

It’s not often that one is better than two. These shock absorbers use a single-walled tube to enclose the piston, the oil and (sometimes) the pressurized gas. These shock absorber types are much more precise at dampening than the standard shock absorber because they are made with considerably more precise standards during the manufacturing process. Additionally, in most cases, the single-wall shock absorber is considerably stronger than the twin-tube shock absorber because they typically use a larger diameter piston. Further, the single-wall absorber is more resilient to shock fade because it can divide the shock’s oil from the air space far better than a twin-tube shock. With this type of construction comes the benefit of better heat dissipation as well.

Reservoir Shocks

When a traditional shock gets compressed where does the fluid go too? It becomes tight and provides very poor dampening do to these high pressures. This is where having a reservoir comes in handy. The little tank on the outside is actually just there as a compression space. It gives us the same effect as though we had a shock that was four-six inches longer without the added travel that we can’t fit. Twin tube shocks try to mimic this design by having a piston chamber and an overflow chamber, but they do it without the valving that the little pipe that feeds the reservoir provides. Adjustable reservoir shocks just allow us to change the firmness of this added space for greater ride control by controlling the nitro/gas in this chamber.

Bypass Shocks

The dampening provided by standard shock absorbers is provided by the valving system being located at the head of the shock piston, which determines the dampening rates. Bypass shock absorbers aren’t all that different in that aspect, but they do add to this standard method of dampening via valving. How? Bypass shock absorbers add the component of external metering valves that are completely adjustable with spanner wrench for changing the rebound and compression of the shock. The other major aspect of bypass shocks is their oil-looping design. As the piston is compressed into the body of the absorber, the oil is pushed through the external bypass tubes and looped back underneath the head of the piston. Transversely, under rebound, the fluid does the same thing, only in reverse. This entire process is metered and dictated at an adjustable rate defined by the external, adjustable check valves. Depending upon make and model, some bypass shocks can offer multiple tubes to the shock body, typically one for rebound and one for compression. Some of which have multiple, adjustable check valves to control the metering of compression and the metering of rebound.

Adding fuel to the fire, yet another reason why bypass shocks are the best of all dampeners is because they’re not only velocity-sensitive like all other shock absorbers, but they are also position-sensitive as well. What does this mean? Simply put, these shocks can use a variable metering system that allows the shock to offer a much softer rebound and/or compression rate initially, and increase the dampening effect as the compression or rebound increases, similar to progressive coil springs. The really cool part? If you have the cash, all of these aspects of a bypass shock can be built to your needs and adjusted based upon the type of wheeling you do!

TeeJay 12-14-2007 07:51 PM

Other things to think about.
Dual Shocks?

If you get frequent heat-induced shock fade and don’t have the budget for reservoir or bypass shock absorbers, you may benefit from running a dual or triple shock setup. However, this doesn’t mean that you just slap another set (or two) of shocks in addition to your existing ones. You should get a set of more lightly valved shock absorbers to replace the ones you have now. The idea here is not the more shock the better, it’s to use the same amount of force, but divide it up between a few pistons.

Upside down?

Unless your shocks are specifically designed to be mounted upside down or designed to be mounted in either direction, please follow the rule stated above for dual shocks. As a rule, dual tube shocks should never be mounted upside down. Some people say that monotube or gas pressurize shocks can be mounted upside down, however in time they will develop and extra inch or more of piston travel that has little to no dampening effect whatsoever. Sometimes a shock must be mounted upside down due to space limitations, or to protect the shock body, if this is the case, make sure you use a shock designed to be mounted upside down. If it’s not, please don’t use that shock.

How can I tell if I need to replace my shocks?

While a leaking shock is an obvious sign of a shock-gone-bad, many shocks wear out without losing any oil. One of the best ways to determine if a shock needs replacement is to perform the jounce test. Simply bounce the front or rear end of your rig by jumping or pushing up and down on it for a few seconds, then let off. If your rig continues to pogo for more than 1 to 1.5 bounces, you may need to replace your shocks.

sgnellett 12-14-2007 08:17 PM

Holy Cliffs Notes, Batman! No offense, dude, but;

TeeJay 12-14-2007 08:23 PM

I tried to separate it by potential topics. There are a lot of things to consider with shocks. I just wanted something that those who were trying to research could find if they searched. It's not really for discussion.

sgnellett 12-14-2007 08:42 PM

I was just yanking your chain! Someone who shall remain nameless published some damn manifesto about why people hate the Patriots, (as if anybody cares!) and everybody demanded cliffs notes, whining about it being too much to read! I opened it up and knew in about one sentence that I didn't give a damn enough to even pretend to read it! :flipoff:

TeeJay 12-14-2007 08:54 PM


I got half way through writing and almost decided that too. I care enough about people not having 5 shocks at each corner though.

sgnellett 12-14-2007 08:57 PM

Excellent! I figure if they have the money to do it and are still stooopid enough to try it, let 'em go for it!

:flipoff: :rofl:

debruins 12-14-2007 10:36 PM

well i read it all, but i cant remember one thing, but w/e i already ahve four shocks and i dont have moeny for more so yyeeaahhh

1BLKJP 12-17-2007 04:49 PM

Excellent thread. I'm moving this to the FAQ section.

meatyjeep 06-17-2014 10:04 PM

I have a 99 TJ. I believe it has a 2.5" suspension lift, but I'm not sure. The shocks are shot and I think they were installed wrong. The boot is on the bottom. (It was bought like that) How can I determine how much lift there is and how can I figure out the correct shock size.

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