Through the 1950s, all domestic trucks featured a ladder frame with leaf springs front and rear. These semi-elliptic springs arch below the framerails. The steering knuckles pivot on kingpins at each end of a solid axle beam. A truck's load capacity reflected its frame strength, axle beam size, steering gear, linkage stamina, spring load rates, and brake capacity.

Use of a beam front axle with a torque tube or Hotchkiss rear axle was common. Ford pickups through 1941 had a transverse leaf spring front and rear with a torque tube rear axle. (Radius rods in wishbone form lend support to the front axle beam and torque tube rear axle.) GM used semi-elliptic leaf springs front and rear with a closed, torque tube rear axle on 1/2-ton trucks through first-series 1955 models. When second-series 1955 GM models rolled from the assembly lines, the solid Hotchkiss rear axle with an open driveshaft became a mainstay for all American trucks.

By the end of the 1950s, the emphasis on ride quality and faster highway speeds demanded better handling. Automobiles had independent front suspension; rear link-and-coil suspension appeared on GM cars. In a bold initiative, the 1960 Chevrolet and GMC light trucks offered rear link-and-coil suspension and independent front suspension (IFS). Unlike GM passenger cars, the double A-arm front suspension used torsion bars instead of coil springs.

The use of torsion bars was not widely accepted. At the time, only Chrysler's cars used torsion bars with IFS. By 1963, GM light trucks adopted double A-arm front suspension with coil springs. Eventually, rear link-and-coil suspension would yield to a traditional leaf-spring layout. A front stabilizer bar, spindles with ball joints, a rear track or panhard bar and other passenger car features were present in GM's 1960 truck suspension-in a far more rugged form, of course!

Ford, Dodge, I-H, and Studebaker light trucks maintained their one-piece beam front axles for several more years. Ford broke ground in 1965 with twin I-beam front suspension. The twin half-axle system closely maintains the stamina and proven worth of beam axles.

These half-axles are offset, and their pivot points overlap. Radius arms support the beams fore-and-aft. Coil springs near each axle end replace conventional leaf springs for longer travel and improved ride quality. Maintaining conventional kingpins and spindles, twin I-beam suspension qualifies as independent front suspension but falls far short of the ride quality and efficient suspension geometry found in GM's unequal length A-arm truck suspension.

Suspension Wear
When inspecting a truck's suspension system, check out all pivots and moving parts. On vintage models, the axle beam must be true, not bent or damaged. Make sure the kingpins and spindles fit properly before checking the beam for straightness. Loose spindle bushings will distort the caster and camber readings. A bent or worn kingpin will also distort these measurements. Camber and caster angles are the best indicator of a beam axle's condition. (Learn more about caster and camber in next month's lesson.)

On kingpin suspension with leaf springs, the spring bushings and shackles are a common wear point. This also applies to rear leaf springs. Later trucks use rubberized spring bushings, which wear and deteriorate over time. Early chassis use bronze bushings at the leaf-spring anchor eyes and the shackle ends. Play, looseness, or deterioration is a sign of failure.

Check for kingpin play by jacking the truck up and placing the beam axle on safety stands. Grip the wheel and tire at 6 and 12 o'clock. Rock the wheel while looking inside at the spindle and kingpin area. (This usually takes an assistant.) Movement between the spindle and kingpin is an indication of play. Anything more than the slightest movement is too much. New pins and new, ream-fitted bushings should fit together with no perceptible play.

Ball joints on an IFS are similar to passenger car parts. The ball joints at the top and bottom of each steering knuckle are a distinct wear point. With a floor jack beneath the lower A-arm, vehicle weight will compress the spring and unload pressure from the spindle's ball joints. You can move the tire and wheel at the 6 to 12 o'clock position and feel for loose ball joints. Ball joints cannot be tested under coil spring load or when vehicle weight is on the tire.

Other wear points are the A- or control arm bushings, radius arm bushings (Ford twin I-beam), sway bar bushings, track bar bushings, and wheel bearings. Inspect leaf springs for misalignment or cracked leafs, loose U-bolts, worn rebound pads, a broken center bolt (which allows axle shift), and worn or damaged spring clips.

Steering Linkage Wear Points
Although steering linkage design varies between beam axle and IFS models, the steering linkage joints are of similar design. Steering linkage must pivot and allow for suspension movement. For this reason, tie-rod ends are of ball stud and socket design. Some pitman and idler arms use a ball stud and socket as well.

On older steering linkage, the joints at the drag link ends, or even the tie-rods, will have spring loaded ball cups. An adjustable plug sets a precise load on the cup tension spring. The steering arms or pitman arm have a ball head, which the cup halves capture-these joints, like all others, require periodic lubrication.

When checking for wear, a dry or semi-frozen joint may not show play. Sometimes, it is necessary to grease a linkage joint to force out dirt and debris before testing for play. A seemingly tight ball stud might become excessively loose.

IFS suspension has the most steering linkage joints. The centerlink or relay rod attaches to the steering gear's pitman arm. The idler arm supports the opposite end of the center link. On double A-arm suspension, the idler arm pivots from the right side framerail. The idler arm is a common wear item. Ford's twin I-beam steering linkage has a simpler "Y" design that uses fewer joints and does not require an idler arm.

When a beam axle model has the pitman arm moving laterally, a drag link or "short tie rod" connects the pitman arm to the steering arm at the right side spindle. A long, single tie rod connects the right and left steering arms. Another approach is the fore-and-aft moving pitman arm that moves a drag link. The drag link attaches to the left steering arm at the knuckle. A long tie rod connects the left and right steering arms.

Steering linkage adjustments include toe-in and centering the steering gear. Next month, our discussion will cover the fundamentals of wheel alignment. Steering linkage and A-arm adjustments are central to frontend alignment. Stay tuned!

What Did You Learn This Month?
Night School would not be complete without a quiz! Don't worry about your test-taking skills or grades. This is an open-magazine, true or false test. Clues can be found within the Night School text, photos and captions. Have a good month!

True or False Questions:

1. A beam axle with leaf springs is a strong, reliable frontend design. Load ratings reflect the beam size, spring rate, frame gauge, and the steering gear and linkage stamina.

2. Loose kingpin bushings and pins cause "kingpin shimmy." Worn ball joints can create a similar effect on A-arm suspension systems.

3. Ford twin I-beam front suspension uses semi-elliptic leaf springs, just like the 1964 and earlier Ford front suspension designs.

4. Frontend wander can be a kingpin issue. It can also be the result of loose leaf-spring bushings, worn shackles, loose tie-rods, or steering gear play.

5. Steering knuckle bushings on a kingpin front axle should be beaten in and out with a broad hammer. If the edges peen over, just straighten them out with a course file.

6. The idler arm on A-arm front suspension moves in unison with the pitman arm. The idler arm mounts to the right framerail. This is a common wear item.

7. Cutting coil springs changes ride height. It also alters the camber angle of the front wheels. If you lower a truck by this method, there will be less suspension travel.

8. If you need to remove a tie-rod end, beat on the end of the ball stud. This will knock the ball stud loose without damaging any parts.

9. Chevrolet and GMC light trucks first used independent front suspension in 1952. The trucks of the '50s benefited from this design.

10. Steering linkage on kingpin front axles is simpler and has less tie-rod ends than double A-arm front suspension. Ford's twin I-beam uses simpler steering linkage as well.

1True, 2True, 3False, 4True, 5False, 6True, 7True, 8False, 9False, 10True

SOURCE
National Parts Depot (NPD Michigan)
2435 S. Haggerty Rd.
Canton
MI  48188
734-397-4569
www.npdlink.com
American Classic Truck Parts
Aubrey
TX  76227
940-365-9786
www.americanclassic.com
Classic Performance Products
378 E Orangethorpe Ave.
Placentia
CA  92870
800-522-5004
http://www.classicperform.com
Bob's F-100 Parts
9372 Mission Blvd
Riverside
CA  92509
951-681-1956
www.bobsf100.com
LMC Truck
15450 W. 108th Street
Lenexa
KS  66219
800-562-8782
www.lmctruck.com
Carolina Classics
624 E. Geer Street
Durham
NC  27701
800-598-4211
www.carolina-classics.com
No Limit Engineering
455 S. D Street
San Bernardino
CA  92401
909-386-7637
www.nolimitengineering.com
Classic Parts of America
1 Chevy Duty Drive
Kansas City
MO  64150
800-741-1678
www.classicparts.com
Sacramento Vintage Ford
24884 Mercantile Drive
Rancho Cordova
CA  95742
888-367-3100
www.vintageford.com
Jim Carter Classic Truck Parts
1508 East 23rd St.
Independence
MO  64055
800-336-1913
www.jimcartertruckparts.com
Performance Online
2572 E. Fender Ave. Unit #A
Fullerton
CA  92831
800-638-1703
www.performanceonline.com
Yogi's Street Rod Accessories
Lawrenceville
CA
800-373-1937
www.yogisinc.com
Bowtie Bits
3101 W. Harry
Wichita
KS  67213
888-838-6887
www.bowtiebits.com
Brothers Truck Parts
801 E Parkridge Ave
Corona
CA  92879
800-977-2767
www.brotherstrucks.com
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