G.T. Inc. (Cepek) Adjustable Shocks

with Remote Control

• Shock Overview
• How They Are Manufactured
• Shock Install

 

Replace This: With

As of Dec 2011 the stock shocks from AMG / Hummer cost 268.00 each. The Cepek shocks are guaranteed for life, adjustable and massive compared to the stock units.

The newest Hummer H1 is now 6 years old. I remember when some of my friends got 2000's which in my mind is considered new. Now those trucks are 12 years old. My 98 is 14 years old. Since most of the Hummers have changed hands, most owners don't have a feel how the trucks are supposed to handle. The shocks in most of the trucks have never been replaced. How many of you have a car that's 10 to 14 years old? There a real good chance that the shocks and struts have probably been replaced at least once or twice. This is probably the most overlooked maintenance item on the truck.

I did the install on my new shocks yesterday. I went to a buddy's shop and we were able to install all four in about an hour and a half. Thanks to Chuck and his website for detailed instructions. Most of the bolts came out very easy, however we did have to heat a few of them up. I am very happy with the new shocks and have noticed a significant improvement in the handling and and ride of the truck.

Mark Weber May 8

I can’t believe the difference they make, and they are so simple to use compared to other systems I have worked with that adjusting them every time the pavement changes seems like it will be a habit.

Pat Mahan November 12

I just installed the shocks on my friend's 12,500 heavy Hummer. Now granted I do not drive the truck very often but when I drove it before it would scare me since it wondered around a lot. If you had to corner very hard the body roll was actually scary. When I test drove after doing the shocks, I pumped them all the way up and the truck felt like mine does when the shocks are set around 3 or 4. I really like the way they increased the performance on my truck and I think they made an even bigger improvement in the heavy truck.

Other then removing the old shocks everything went smoothly. They worked the first time I started them up and if there are any leaks they must be very small because the system seems to hold pressure very well. Since I have the XLC2, I run the rear shocks fairly lightly most of the time 2-3 and the fronts 4-5. I did try the 6-7 range which was great for cornering on some back roads, but the wife complained too much road bounce and wasn't wearing a sports bra to keep everything adequately supported. I offered a few extra bungee straps, but that only brought a cold stare. I backed off the shock setting.
Later Myk Manon

The Hummer has a 4 wheel independent suspension with a coil spring and shock located in the center of the spring at each wheel. The shock absorbers job is to control the springs. When you hit a bump it's the spring that absorbs the lions share of the energy. It will compress and then 'spring back'. In fact without a shock the spring will continue to oscillate back and forth (twang) until the energy in the spring is used up. This, of course causes instability in vehicle handling. Imagine hitting a big off road dip. You want your truck to come back up and stop, not to continue bouncing up and down. Shocks are often called dampers because that's what they actually are. Their main job is to dampen the spring oscillation. Worn shocks can cause premature tire, steering and suspension component wear. They also cause dangerous instability through excessive sway.

A spring is made of steel and like any steel it weakens every time it flexes. If your shocks are bad or not properly set up for the kind of driving you do the spring will not be damped and continue to cycle. This causes the steel to fatigue which is why springs prematurely wear out.

The most difficult question is "how do you know if you need new shocks?". A Hummer weighs 6 to 8 thousand pounds and has springs that rival a railroad car. In a lighter weight vehicle you can push down on a corner and let go. The car will rise up and settle right down if the shocks are good. If the car continues to bounce it needs new shocks. I defy you to push down on the corner of a Hummer and see if it will bounce. The way I knew I needed new shocks was through sway. I started to notice when going around turns, especially on highway entrance and exit ramps the truck wasn't as 'rock' solid on the road as I thought it should be. Another test would be to take the truck slowly over a bump or through a dip that would cause it to bounce. See if it bounces as you come off the obstacle.

Tom Cepek told me that Rod Hall once said that if you have 2,500 miles on your factory shocks you need new ones. The way the story goes is that Rod picked up a new Hummer at a dealer out of state and had it driven back to his shop. When it arrived they had to replace the shocks. My take on the situation is that Rod Hall is much more demanding of their suspension system due to the extreme punishment they put a truck through during a race. The factory shocks are generic oem's made by Monroe. My guess is if you have over 20,000 miles on your truck you probably need new shocks.

Once I decided I needed new shocks I quickly found out that there are not many choices available. The only ones I found are the factory shocks, Rod Hall Racing shocks and the Cepek's. Note that the front and rear factory shocks are different part numbers because they are valved differently. The Rod Hall shocks are designed for punishing off road racing where the truck is traversing rough ground at high speeds. The suspension is being worked at a rate that far exceeds anything I'm going to put my truck through; this is why you need the remote reservoir (for cooling).

The Cepek's are adjustable, physically larger and have a lifetime warranty. Because they are adjustable you use the same shock on all 4 corners of the truck. They also have a remote adjustment option which will let me tailor the shock stiffness to the kind of driving I'm doing while sitting in the truck. This will let me experiment with different road conditions.

I've had the shocks installed for awhile now and I'm getting spoiled. When I first received them I thought I would install the shocks without the remote adjustable feature. I asked myself "Why do I need to play around with the shock damping?" Now that I have it I can't live without it. If I'm on the highway I set them up stiffer just to see how fast I can come off the exit ramp. When I'm cruising I set them soft for a nice smooth highway ride. Around town I want enough firmness for good handling but I don't want to feel every bump in the street. I even find myself softening up the shocks when I'm coming to a railroad crossing or a potholed street in the city.

I tested the shocks out at the Hummer Club's Durango Moab event in September 2003. Almost all of the trails were slow extreme rock crawling. When the truck goes through what I call a 'whoop te do' (2 to 3 mph) where the right and the left go through a smooth deep dip at different times causing the truck to heave slowly around in all directions the soft setting, 0 would let the truck rise up pretty high. It wouldn't oscillate, but it did heave. Turning the shock damping up to 9 seemed to really tame it down and give me more overall control.

Many of the moves consisted of riding the brakes down a steep stair step while trying to go slow enough so you don't bash your bottom and trailer hitch on the rocks. I started by setting the shocks on the softest setting, 0. I found that the truck was bottoming out on many of the deep dips. I experimented with higher settings (more damping) and ended up running with the front and rear set on 7. This seemed to give me much better control and kept the truck from banging the bottom. I did use 9 on some of the extreme stuff. Raising the stiffness didn't affect the bumpiness of the ride because of the slow speed and 18 to 25 psi tire pressure.

This is how the shocks work.

Each shock has a spring loaded piston valve at the bottom that regulates the shock's stiffness. With the valve all the way up and no pressure the shock is at it's softest setting. As the valve is pushed down the shock gets stiffer. The shock valve is adjusted manually by using the dial which is nothing more then a screw pushing the piston.

The remote adjustable unit works by regulating the air pressure pushing down on the shock piston valve. A small computer controls a miniature compressor that maintains the pressure at a user defined set point independently for the front and rear pair. By monitoring the air pressure the computer knows when a problem such as a leak occurs.

This is what the manual says about the shocks.

The G T Inc. (Cepek) Deluxe Digital Remotely Adjustable Shock Control Unit is one that is very user friendly and easy to use. Once you understand the basics of the system, what it will do, and what you can expect from the programmed functions.

Basically, the system allows you to set the damping of the front and rear shocks independently, with each pair of shocks having an allowable setting parameter of 0-9, or 10 total positions of damping, 0 being the softest, and 9 being the stiffest, as well as a memory channel that again, allows settings of 0-9 or 10 programmable settings.

The user can input shock damping settings into each of the 10 memory channels and store those settings for future and continued use. The user then, only has to cycle through the memory channels by cycling through those numbers with the center push button and then stop on the preset shock damping setting they would like use.

As described above, the system:

1. Allows the user to set shock damping independently front and rear,
2. Has user programmable memory channels
3. Provides aural and visual warnings
4. Maintains pre-selected shock damping by constantly measuring line pressures and adjusting them as necessary,
5. Gives a warning if the compressor adjusts line pressure more than 6 times in one hour if on the same setting
6. Shuts down the compressor should a line break, be cut or pulled loose to prevent compressor damage
7. Allows manual changes to pre-selected shocks settings without changing the pre-programmed settings.

The unit draws between 10 and 15 amps, typically 12 amps when the compressor is running. The control unit draw is negligible.

It is suggested that you may want to group your settings in order to keep like terrain, street, off-road, severe handling and other settings in close proximity in order to make it easier to remember the location of each setting. For example 0-2 could be your street handling settings, 3-6 could be your off-road settings, and 7-9 could be your mountain driving and/or towing settings.