Checking Your Front End & Alignment Specs
Updated April 15, 2009
Before you do anything check your idler arm, pitman arm and center link; in fact check all the front end parts. The holes on the end of the center link attach to the tie rod ends which in turn connect to the steering arm on the geared hub. This is what turns the truck.
In 1995, AMG upgraded the center link from 7/8" thick to 1.25" inches thick. This heavy duty bar was installed on trucks with VIN 163985 and later.
Trucks without the new center link require a spacer when installing the latest Idler Arm or Pitman Arm to ensure that the slotted nut will line up with the cotter pin hole. If you install the new center link you must upgrade to the new idler and pitman arms. The original center link is no longer available.
How do you check a center link?
There are only two sure-fired methods I know of;
1.) Remove the center link and have a complete layout inspection performed
2.) Remove the center link and use a checking fixture designed for this center link.
Both the above methods will require a copy of the latest & greatest center link blueprint plus lots of $$$$!!! Of course there is always the option of changing out the center link with the latest & greatest center link (AMG p/n EC600386889) for 10,300 GVW HUMMERs for around $215.
Finally, there is the real quick & dirty method. With the front wheels straight ahead, stand in front of your vehicle 20-25 ft. back. If your front wheels appear to be TOED-OUT, you could have a bent center link.
The center link holds the whole front end together. Most center link problems occur off road when you come down hard on the front end and a rock bends the link. The holes in the link can wear over time especially if any of the bolts come loose. A center link problem will completely throw off your alignment. You will probably notice that your steering wheel is not centered anymore. It will drastically change the toe settings which can cause a set of tires to wear out very fast.
Earlier model trucks (sometime in 1995 and earlier) have a different center link. If you are going to upgrade to a new idler arm and pitman you will have to replace the center link. also.
How Much Time and How Much Does it Cost to Align a Hummer?
The time it takes to align a Hummer is really dependent on what year you have and what's out of adjustment. The Hummer needs alignment on all 4 wheels. You also have to make sure that all the front and rear end suspension and steering parts are in good repair. It's a waste of time and money to try to align a truck with bad ball joints, bad tie rod ends or a loose idler/ pitman arm, bent centerlink, worn A arm bushings etc.
My front left had a broken adjuster cam sometimes call an eccentric. The cam itself was split and when you turned the pivot bolt the cam didn't move. On my rear right one of the adjuster bolts was rusted to the inside of the A arm bushing. Whenever we rotated the pivit bolt to adjust the camber it would spring back because the seized bolt was now effectively a part of the rubber bushing. The rule is check all these parts before you get started. The cam's part number is 6009537 and the bolt is 6009807.
Your spring height is critical to alignment. Spring height will affect your caster and camber. As the springs sag the camber goes negative (wheels splay out). That's why the trucks have a positive camber to begin with. As you add weight the truck settles down, compresses the springs causing the camber to even out. If it's bad enough there won't be enough adjustment in the cams (98 and newer trucks) to overcome the negative caster.
The idler and pitman arms are what hold the center link in place. If either of these parts sag it will change the postion of the center link. Since the tie rods are attached to each end of the center link, the change will effect the toe and the steering wheel position.
If you want a good job pressure wash underneath the front and rear making sure to get the top of the A arms and the tie rods. Then soak the tie rod threads and the A arm adjusters with WD-40 or PB Blaster.
The shop you bring your truck to should have the latest high tech equipment. Shown is a Hunter DSP 600 (2006). All you have to do to set the truck up is to mount the remotes on each wheel. A laser head picks up reflections from each wheel and a program tells the operator using graphics exactly what to do. The screen had a picture of the upper A arm with arrows pointing to the adjusters.
The simplest alignment is setting the toe. This can be done as fast as any regular car or truck. The problem comes in when the tie rods are frozen and won't turn which is a common occurrence on Hummers. You have to spend time heating them up with a torch and or taking them off the truck to loosen. Worst case they have to be replaced. That's why I antisiezed all the tie rods on my truck when it was new. I can have the 4 wheel toe set at any place that has a lift with enough capacity for the Hummer for around 30 to 40 bucks.
If you need to set the caster and camber the job just became a lot harder. On trucks built before 1997.5 and Hmmwv's these adjustments are made by adding and removing shims behind the upper A arm mounting bracket. This means that you have to put the truck on the alignment rack, take a reading, calculate what shims you need, remove the tire, remove the A arm bolt, loosen the screws on the A arm brackets, add or remove shims, do this for at least both rear or front wheels, put it all back together tight, set the alignment machine back up and hope your reading is now correct. It can take 1 hour per wheel to do this. The good news is that once the caster / camber on these trucks is done it almost never needs to be redone unless the frame or other parts bend. A full alignment on one of these trucks can easily take 8 hours to do.
On newer trucks 1997.5 and up, AMG has installed adjustment eccentrics which are cams to set the caster and camber. This makes the job easier but not foolproof. The catch here is that the adjustment locking nut has to be torqued to 260 ft lbs so it doesn't loosen. When these first came out II remember seeing one in the parking lot at the Black Hills off road event that looked like someone kicked both rear wheels in at the bottom.
Most regular alignment shops don't have the big tools to loosen or tighten these nuts. The nuts are impossible to get at with full size 3/4 drive sockets. What you need is a 1/2" drive 300 ft/lb torque wrench with a short 1-1/8" socket, an 1-1/8" open end wrench, a 3' piece of pipe and a 1/2" breaker bar. A 1/2" drive 300 ft/lb torque wrench is rare. If you don't have one tighten up the nut with a breaker bar and the pipe till is won't turn anymore. I recently had my front done and it took 3 hours and cost 110.00 (9/2006).
The real pain is when you set the camber and then tighten the nut the camber changes. You have to play around and build in some adjustment to anticipate the movement once the nut is tightened. The adjusting mechanism can also be bent. We couldn't get the right angle and leverage to loosen one of the rear cam bolts so we raised the truck on the hoist so the wheel dropped down giving us more room to work. The bolt was so stubborn we ended up removing the rear wheel.
Once you loosen the nut you need to separate the ends of the control arm bracket. The A arm bushings have serrations on the ends that are there to keep the cam from rotating when the assembly is tight. You need to make sure that the bushing is broken free of the bracket. Make sure the nut is very loose. Take a crowbar and wedge the ends apart from the bolt. Snug the nut back on so the cam stays straight. Don't over tighten of you won't turn the cam. Then adjust your camber/ caster.
If you can't get enough adjustment with the cams you will have to add shims. If this becomes necessary check for bad A arm bushings, damaged cam adjusters or damaged suspension parts. It also could be an indication of a bent frame. Also check for cracks in the A arms especially around the ball joint bolt holes.
Make sure that the lift and the center jacks will raise an 8000 lb Hummer.
Go to Hunter if you need help finding shops that have the latest laser gear.
Using or Converting Back to Shims
I know that some owners have converted their trucks back to the shim system. Others have tack welded the adjustment bolts so they won't come loose. All this playing around can take time. I spoke to a tech at one of the busier Hummer dealers. He said that they have converted a bunch of trucks. He advised that you should only convert the rears because they rarely go out. The fronts will go out of alignment whether you have the shims or the cams.
If you convert back to shims here's a starting point for shimming the wheels. There are 3 types of shims.
- tapered shims .230 to .150
- Thick .120 - 3 mm changes caster / camber +.6 degrees
- Thin . .060 - 1.5 mm changes caster/ camber +.3 degrees
A cup or pocket is Hummer tech slang for the A arm bracket.
Camber is changed by inserting the same thickness shim in the front and rear pockets of an A arm. Camber, which only pertains to the front is increased by inserting shims in the front A arm pocket only.
If you need a place to start, shim the rears with 2 thick shims (.060) per cup / pocket. For the front put 4 thick shims in the front pocket and 2 thick and one thin in the rear pocket. The tapered shims are used on the front A arms, front pocket. I don't know if they were used on all trucks.
The Alignment is Fine but my Steering Wheel isn't Straight
You need to adjust the front toe so both wheels are shifted equally to the right or the left depending on your steering wheel error. If your steering wheel is turned to the right as you drive straight down the road this means that the front wheels are pointing too far to the left trying to steer the truck off to the left forcing you to turn your steering wheel to the right to compensate. What you have to do is adjust the front wheels so they both point straight. In this case both front wheels need to be turned an equal amount to the right to bring them to center. To do this you will need to increase the toe on the left front (this turns the LF wheel to the right) and decrease the toe on the right front (this turns the RF wheel to the right) the same amount. If your steering wheel is turned to the left you do the opposite.
To do this you have to loosen the front tie rod clamps and turn the adjusting sleeves. It usually only takes a quarter turn. Make sure you know which way to turn the sleeve. This can vary depending on how the rods were installed. See the tie rod install article for more info.
Always align the rear first.
Set the front and rear camber as close to 0 as you can but keep it positive.
Set the caster (which as you know is only on the front) to around 3. The left side can be a little less. This will compensate for the crown in the road pulling the truck to the right, but this is really splitting hairs. The caster is not that critical. Set the front toe about 1/8" in. Set the rear toe to 0. Each turn of the tie rod changes the toe about 3/8".
1998 and new trucks use cams to set the caster and camber. Once the cams slip, even 260 lb-ft is not enough to keep them from slipping again. I recommend to everyone that they have the cam bolts tightened to around 300 lb-ft. Some owners have replaced the cams with the older style shims. Some shops have actually tack welded the cams so they don't move. The weld can be easily broken if adjustment is necessary.
If your steering wheel isn't lined up straight all you have to do is turn each tie rod in the same direction exactly the same. Most times all it takes is 1/8 to 1/4 turn. Doing this maintains the same toe setting while moving the steering wheel. If you turn the tie rods unevenly you will screw up the toe setting.
The thrust angle
is defined as the deviation between the bisector of the total rear toe angle of the vehicle (the thrust line) and the vehicle centerline.
This is a tad more complicated than is sounds.. the centerline of the vehicle is defined NOT by the axle midpoints, but rather by the position of each of the vehicle wheels. In an extreme example, imagine a car which is narrower in the front than in the rear. If you draw lines connecting the tires on the left side of the car (front & rear) and the tires on the right side of the car (front and rear), the lines will intersect at some point in space out in front of the car. Bisect the angle formed by the intersection of these lines, and you will have the centerline of the vehicle's wheel system. Usually this is very close to the chassis centerline (as measured by the axle midpoints), but it's not exactly the same.
Next, to determine the total rear toe angle, the toe angle for each rear wheel is determined relative to the wheel system centerline. The sum of these angles is the total rear toe angle. If you project lines parallel to the face of each rear wheel, the two lines will intersect somewhere at a point unless the wheels are exactly parallel to each other. The angle at which these lines intersect is the total rear toe angle. Bisecting this angle with a line yields the thrust line of the vehicle. This is the direction the two rear wheels of the vehicle would travel if allowed to just roll along.
Finally, the angle measured between the vehicle's wheel system centerline (as determined by the position of all four wheels) and the thrust line of the vehicle (determined by the pointing direction of the rear wheels) is measured as the thrust angle.
When I accelerate the hummer pulls to the right, let off the gas and it goes back to the left. There's not any play in the steering at all. Traveling on uneven roads the truck wanders to the left or right.
What off-set wheels do you have and are they factory tires or aftermarket ones? The non factory tires sometimes are not rated for the weight of the hummer and the belts can separate. Some aftermarket wheels have the wrong off-set and can cause the geared hub clamp nuts to loosen and cause play in the geared hubs. This is a very dangerous condition because you can loose a wheel while driving.
Another common cause of the pulling problem is different size tires. A new and an old tire (of the same size) can easily cause this problem. If it tends to want to turn the wheel, it is most likely on the front. If not, most likely the rear.
Problem with The String Method
Setting the toe using the 'string' method is problematic because the thrust angle is a measurement of how parallel the tire is to the frame. You could set your rear toe angle correctly and still have both tires pointing left or right in relation to the frame of the truck.
Chuck as far as I am concerned, you are 100% correct!!!
What you mentioned is sometimes referred to as the "Total Toe." If the "Total Toe" is off from the get-go (right to left/left to right) the results of any other field measurements and/or corrections will also likely be off..