Torsion Bar Adjustment

spackelman · February 8, 2007

The "Z" measurment on my 4 x 4 2002 2500HD CCLB measures about 3" on left side and 4.25" on right side. It has been like that since I bought the truck new. Never thought anything about it. I'm thinking this might have had something to do with the front hub bearings going bad.

The factory "Z" height says about 4.5".

Going to adjust tonight. The question is do I use the "Z" dimension as a guide or do I measure some place else (like bottom of wheel to fender well) or maybe just both?

My other question is should I raise the left side a little (1/4" or so) higher to compensate for the driver (me, about 200#) and the fact the fuel tank is on that side.

I'm not looking to level out the truck, just get it back to original specs, +maybe a tad higher.

Thanks for any advice.

Also, what is the life span of the torsion bars??

ChevyTech007 · February 9, 2007

Trim Height Specifications

Drive Type/Model

Service Allowed

Service Preferred

Z Trim Height: Models with torsion bar suspension must be adjusted before aligning the vehicle.

C1500

86-98 mm (3.3-3.8 in)

92 mm (3.6 in)

C2500

K1500

K2500

C/K3500

C/K3600

110-122 mm (4.3-4.8 in)

116 mm (4.5 in)

Z height is measured by a parallel line through the center of the lower control arm bolt and a parallel line from the bottom of the spindle. The distant between the two lines is the Z height. You could measure this with a helper to hold two levels and you measure the distance between the levels.

spackelman · February 9, 2007

Thanks for the info.

I did the adjustments on my t-bars. Made a nice difference in the ride.

Z dimensions - left side 4 3/8", right side 4 3/4". Then I measured from the bottom of the wheel (rim) to the bottom of the fender well - 32 7/8", both sides.

But the truck seems to lean to the right. Taking some other measurments at the fenders and the box, the right side is a little lower than the left, but the "Z" dimension tells me the right side should be slightly higher. I'm confused.

Do I focus on the "Z" dimension and get the 2 sides perfect?

My driveway is slightly sloped to the right. I will check again on another surface.

bobcat5544 · February 9, 2007

CORRECT WAY TO MESSURE RIDE HEIGHT WITH TORSION BARS

Trim Height Inspection

Trim Height Measurements

Trim height is a predetermined measurement relating to vehicle ride height. Incorrect trim heights can cause bottoming out over bumps, damage to the suspension components and symptoms similar to wheel alignment problems. Check the trim heights when diagnosing suspension concerns and before checking the wheel alignment.

Perform the following before measuring the trim heights:

Make sure the vehicle is on a level surface, such as a alignment rack.

Remove the alignment rack floating pins.

Set the tire pressures to the pressure shown on the certification label. Refer to Label - Vehicle Certification in General Information.

Check the fuel level. Add additional weight if necessary to simulate a full tank.

Make sure the rear compartment is empty except for the spare tire.

Close the doors and hood.

Z Height Measurement

Important: K models only the Z height must be adjusted before the alignment.

The Z height dimension measurement determines the proper ride height for the front end of the vehicle. Vehicles equipped with torsion bars use a adjusting arm in order to adjust the Z height dimension. Vehicles without torsion bars have no adjustment and could require replacement of suspension components.

Important: All dimensions are measured vertical to the ground. Cross vehicle Z heights should be within 12 mm (0.47 in) to be considered correct.

Place hand on the front bumper and jounce the front of the vehicle. Make sure that there is at least 38 mm (1.5 in) of movement while jouncing.

Allow the vehicle to settle into position.

Measure from the pivot bolt center line (2) down to the lower corner (5) of the steering knuckle (1) in order to obtain the Z height measurement (4).

Repeat the jouncing operation 2 more times for a total of 3 times.

Use the highest and the lowest measurements to calculate the average height.

The true Z height dimension number is the average of the highest and the lowest measurements. Refer to Trim Height Specifications .

Z Height Adjustment

For vehicles equipped with a torsion bar suspension turn the bolt (1) that contacts the torsion arm clockwise to raise the and counterclockwise to lower the height adjustment. One revolution of the bolt (1) into the nut increases the Z height by approximately 6.0 mm (0.2 in).

For vehicles without torsion bars, replace damaged or worn components as necessary.

D Height Measurement

Important: There are no specified trim heights specifications on leaf spring vehicles because it is not an adjustable feature. The height of the suspension will depend on the option content of the vehicle as well as the aftermarket equipment that is placed on the vehicle. The measurements are used for comparison only and should be within 15 mm with the vehicle at curb and no accessories.

With the vehicle on a flat surface, lift upward on the rear bumper 38 mm (1.5 in).

Allow the vehicle to settle into position.

Important: Measure the metal to metal contact points of the rear axle to the frame on the inboard side of the leaf springs.

Measure the D height by measuring the distance between the bumper bracket and the top of the rear axle tube.

Repeat the jouncing operation 2 more times for a total of 3 times.

Use the highest and lowest measurements to calculate the average height.

The true D height dimension number is the average of the highest and the lowest measurements.

If these measurements are out of specifications, inspect for the following conditions:

• Sagging front suspension

• Refer to Front Coil Springs Replacement or Torsion Bar Replacement in Front Suspension.

• Sagging rear leaf/coil springs

• Refer to Leaf Spring Replacement in Rear Suspension.