Mechanics

CHEVROLET MALIBU TIRE PROBLEM

2005 Chevrolet Malibu • 60,000 miles

I had my transmission taken out and repaired and after reinstallation, I noticed that the car now does not steer in a straight direction. This problem was not present before the transmission repair. Would the reinstallation of the transmission cause this steering problem.
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October 27, 2012.




ABSOLUTELY, and this is strictly a GM problem, and a very common one. To remove the transmission or the engine, the engine "cradle" has to be lowered with all the drive train components on it. Experienced mechanics who do this will use spray paint to mark the orientation where the four large bolts were in relation to the mounting holes so they can put it back the same way. When they don't pay attention or aren't aware of this, the entire cradle can be moved to either side quite a bit. It's easier from an alignment point of view to think of it as the body is moved sideways on the rest of the car. That moves the tops of the two front struts to one side also and that's where your problem is coming from. The lower ball joints and the tops of the struts are the pivot points that let the wheels turn left and right. As viewed from in front of the car, those struts are tipped in on top a lot. By shifting the cradle off-center, one strut and its two pivot points are standing up straighter than normal and the other one is laying down flatter than normal.

One of the three basic alignment angles is "camber". That is how the wheels are tipped left or right on top as viewed from the front. Moving the tops of the struts moves the tops of the wheels and they will pull very hard in the direction they're leaning. Camber is adjusted during an alignment but in this case it will not help; in fact, it can make the handling undriveable. The car will dart all over the road based on bumps and the up and down suspension travel. The secondary alignment angle involved is called "steering axis inclination", (SAI). It is always shown on the printouts from alignment computers, but we rarely look at it unless we're looking for the cause of an elusive problem. There is never a specification given. All that is required is the value is the same on both sides, typically within 0.2 degrees. 28 to 32 degrees is common but the exact value isn't important.

Shifting the engine cradle to one side changes SAI and the ONLY way to make it correct is to shift the cradle back, then remeasure it on the alignment computer, THEN continue on with the normal alignment. Assuming your alignment was correct before, meaning a straight steering wheel, no pull to one side when you let go of the steering wheel, and even and smooth tire wear, all that is needed now is to shift the cradle back to where it was. That might be possible to do if there are "witness marks" in the rust or paint on the cradle to show where it was. If those marks can't be seen, the only way to make it right is on the alignment computer. As it is shifted, you'll see the numbers on the screen for camber and toe come right back into specs and turn green, meaning they're close to "in specs". No other adjustments should be needed.

If the car wasn't in perfect alignment before, SAI still has to be corrected, then the normal part of the alignment can be done.

It's interesting to note that Ford has had a lot of problems with this too but it was due to the poor design of their cars. In the 1980s they had some models that had the camber adjusted during an alignment by moving the tops of the struts left or right and that changed SAI too. A lot of people noticed their cars handled differently when camber had been changed. In later years they didn't even bother to provide a means of adjusting or correcting camber. The Escorts and Tempos were perfect examples. Camber was messed up REAL bad to make the cars ride smoother than competitors' cars during a test drive, so they sold a lot of them, but then the unsuspecting owners found out tires were chewed off in 15,000 miles and there was nothing you could do to fix that except keep on buying tires. 0 degrees of camber means the wheel and tire are perfectly straight up and down. (90 degrees would mean the wheel was laying on its outer side against the ground. A typical camber specification is between 0.00 and 0.50 degrees positive, meaning tipped out on top, but not nearly enough to see by eye. Camber on the Escorts was 2 7/16 degrees on the left wheel and not adjustable! The rear tires were tipped in on top a ridiculous amount but the aftermarket parts suppliers came up with modification kits to fix that poor design. We used to laugh when we'd see those cars going down the road. It looked the tires didn't know which way to go. Ford tricked a lot of people, but they're still doing it today.

On other brands of cars and trucks, measuring SAI is a quick and accurate way to determine if there is damage from a crash that wasn't repaired properly. Bent parts and a bent frame will cause SAI to be different on each side. If SAI is very close to the same on both sides, the car should be able to be aligned to handle normally and have no abnormal tire wear.

Caradiodoc
Oct 27, 2012.


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