Mechanics

FORD F-150 TIRE PROBLEM

1972 Ford F-150 • 100,000 miles

1972 Ford 4 wheel drive - need to figure out how to straighten drivetrain.


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Kar623
March 26, 2013.



Kinda depends on what's wrong and the cause.

Caradiodoc
Mar 26, 2013.
Added lift kit and it pushed front end axle way over to one side. Is that enough information to give an answer?

Tiny
Kar623
Mar 31, 2013.
Nope. You have to pretend I can't see the truck. I don't have a listing for an F-150 in '72 so I used an F-100 for reference. Some models have coil springs in front, and some have leaf springs. I don't think Ford had come up with the twin I-beam suspension yet at that time. That is a disaster as far as tire wear. The critical thing to reduce tire wear is to have the suspension at the specified ride height. As the springs sag with age the tires are going to tip in on top and they will ride on the inner edges. Accelerated right front tire wear was another common problem that was reduced by installing a heavy duty strut rod bushing and heavy duty shock absorber. Of course you would replace the left ones too but they were really needed on the right side.

You also have to look at how the ride height was altered. If spacers are installed between a solid axle and leaf springs, the leaf springs set the position of the axle and it won't shift to the side but the geometry between the ball joints and steering linkage pivots will be messed up. Handling will be reduced and lawyers and insurance investigators know that. They will convince a jury you were partly at fault for the crash when the other guy ran the red light because you were less able to avoid it, and they will be right. There is nothing you or I can do to improve the handling beyond what the engineers designed in. We can only make it worse by altering things.

When coil springs are used many people start by installing longer springs or spring spacers. That won't make a big impact on tire wear with solid axles but with the twin I-beam that will tip the tops of the tires out. Look at any Bronco II on the hoist and see how badly the tires tip. That axle design is a compromise between the strength of a solid axle and the ride quality of independent suspension, but it is the worst possible design for good tire wear. Raising the ride height on purpose or lowering it due to weak springs will tear up the tires worse than normal.

For some applications "drop spindles" are available but not for four-wheel-drive front axles. They move the wheels lower on the spindles. That raises the truck higher off the ground but it does not change the suspension ride height. Think of driving onto a pair of 2" x 6" pieces of lumber. The frame and body will be an inch and a half higher off the ground but the suspension geometry and its relationship to the steering linkages will not change. The three main alignment angles will not change but a secondary angle called "scrub radius" will be affected. If you stand in front of the truck and draw an imaginary line through the upper and lower ball joints, that line intersects the road surface at a specific point in the middle of the tire tread. That angle was carefully designed in and it is critical it be exactly the same on both sides to maintain control when driving over bumps in the road, and for even braking with no pull to one side. Even when it is equal on both sides, changing scrub radius changes how the truck reacts when hitting bumps and especially when hitting bumps while braking. Larger diameter tires, and wheels with a deeper offset change scrub radius and reduce handling. Trucks are normally raised to allow the installation of bigger tires. It's those tires that change scrub radius as do drop spindles. Spring spacers don't change scrub radius by themselves but the tires still do.

As you can see there are a lot of variables. I need to know the type of suspension you have and how the truck was lifted to figure out what would cause the axle to shift position. Any chance you can post some photos of the springs and any parts that were altered?

Caradiodoc
Mar 31, 2013.