While driving SUV pulls to the left?

Tiny
MISSSNOW
  • MEMBER
  • 1999 FORD EXPEDITION
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
Got brakes done. Just got suspension conveyed. Truck still pulling all over. Pulls very hard to left. Shop said they don't know.
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Saturday, March 6th, 2021 AT 5:35 AM

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Tiny
CARADIODOC
  • EXPERT
This is a job for the specialists at any tire and alignment shop. They're experts at finding the causes of pulls, vibrations, and bad tire wear patterns. They'll start with a steering and suspension systems inspection. Different parts require the vehicle to be raised up and supported in different ways to "unload" those parts so wear and objectionable movement will be evident.

Typically the next step will be an alignment, or at least an alignment check. There's three main alignment angles we start with. The first is "camber". That has to do with how much a wheel leans in or out on top as viewed from in front. Both sides must be in specs for acceptable tire wear, but both sides must be very nearly equal. The tires want to roll in the direction they're leaning. By being equal, their pulls will offset each other. If one leans out more, the truck will tend to pull that way.

"Caster" is harder to describe but you can visualize it if you look at the front fork of a bicycle and how it angles rearward at the top. This angle has very little affect on tire wear, but again, both sides must be equal. Caster has the biggest effect on how the steering system comes back to center when you let go of the steering wheel after going around a corner. Both camber and caster are measured in degrees. The truck will pull toward the wheel with the lowest caster reading. A camber pull to the right can be offset with a caster pull to the left, but caster has half the effect as camber. That mismatch can make for a fairly unstable vehicle to drive, so while we have to offset one a little with an opposite pull on the other angle, that has to be kept to a minimum.

When caster and camber are adjusted, the last angle to be set is "toe". That's the direction the wheels are steering when the steering wheel is straight. In the most basic terms, "toe-in" means the fronts of the wheels are closer together than the rears, or they're both steering very slightly toward the center of the truck. A little toe-in is usually specified. Road forces pull the tires back and makes them perfectly parallel when you're driving. That provides best tire wear related to that angle.

If the front wheels have some "toe-out", they're steering away from the center of the vehicle. It can only follow one tire. That's the one with the most weight on it, and that's usually the right one. When you hit a bump or cross an intersection, more weight might transfer onto the left tire momentarily, then the truck will veer that way. Excessive toe-out makes for a very tiring and miserable vehicle to drive. That shows up in the tire wear patterns too.

If the alignment is okay, an elusive cause of pulling can be unequal rolling forces between the tires. That's not really a defect. To identify that, we switch the two front wheels / tires side-to-side, then go on a test-drive. Sometimes the pull will be gone, in which case we're done. If it pulls the other way now, the tires can be switched front-to-rear. If you switch them on one side first, you can figure out which tire is responsible. If you don't care to know, just switch all four at once and leave them there until one pair wears out.

A sticking brake can cause a pull too. You didn't say if the brakes were done to try to solve the pulling, or if the pulling started after the brake job. Light, or subtle pulls can be hard to identify and correct. When you have a hard pull as you described, finding the cause shouldn't be difficult, but it is usually a job for the specialists.

Worn rubber control arm bushings can cause pulls too by failing to hold a wheel in alignment. Those will show up with during the inspection. You may also notice a change in the pull or in the position of the steering wheel depending on whether the brakes are applied.
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Saturday, March 6th, 2021 AT 3:31 PM

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