Last month, I took my friend's 2006 Prius to a Pep Boys for four Cooper CS4 Tourings and an alignment.

After the alignment, I noticed that the steering wheel was not centered and the car still drifted to the right, especially on the highway. Here were the alignment specs at that time:

Front:

LF Toe: 0.00
RF Toe: 0.05

LF Camber: -0.4
RF Camber: -1.4

Rear:

LR Toe: 0.05
RR Toe: 0.10

LR Camber: -1.2
RR Camber: -1.7

So, I knew I needed to take the car back since the steering wheel was off-center (due to tech error). But according to the results, the RF camber needed some correction as well. So, I purchased a Moog "Fast Cam" bolt, which features 1 degree of +/- correction.

Fast forward to today. I removed the RF upper strut mounting bolt and replaced it with the Moog "fast cam" bolt. I fiddled with the bolt until the washer and bolt head seated flush with the strut. When I was finished, the the washer handle was pointed towards the outside of the car, as was the the "-" imprint on the bolt head (IIRC, this means the lobe was opposite the washer handle). I did not touch the lower bolt aside from checking that it was properly tightened.

My friend and I took the car for a drive down the Hwy 17 and the car suddenly tracked straight. It no longer drifted to the right! Normally, when you install a camber bolt, you are supposed to loosen both strut mounting bolts, then turn the camber bolt in order to get any adjustment. But I didn't do anything besides installing the camber bolt, as I was planning to drive it straight to the shop to have it aligned anyway.

At the shop, they mounted the car back on the rack and took measurements. Now, the LF camber was reading -0.7 degrees and the RF camber was reading -0.9 degrees-- which is right in the middle of the allowable range. The tech went ahead and reset the RF toe to 0.00 degrees (from 0.05 degrees), and sent me on my way. (The LF toe was still at 0.00, so he didn't touch that.) On the drive home, my friend was able to drive at 70mph for minutes at a time without holding the steering wheel-- the car stayed straight!

So, what do you guys think happened? I didn't actually "turn" the camber bolt to perform any form of adjustment, yet the camber problem magically cured itself. Could the chamber have changed simply from removing/reinstalling the upper strut mounting bolt?

If this car is the same as other designs I've seen, The adjustment is only done from the top and the bottom are simply mounting bolts correct?

If so then yeah, moving the top angle that small of an amount would probably be easily possible especially if the suspension moved at all while you had the bolt loose.

You haven't mentioned anything about caster. Depending on the design of the suspension, a small tweak on the camber bolt may have changed the caster, bringing it to where it should have been.

Yeah, I'd say that in checking the torque, you inadvertantly moved it and hit on the right setting. When you are talking tenths of a degree, just the act of moving a bolt could be enough to change the reading.

I bet there's a variable amount of "sticktion" in the bushings especially in the time when the tech (of varying weight) gets out of the car when it's up on the turntables. The rims would likely move a few mm while the tires remain planted, creating stress.

An interesting experiment would be to drive the car in and out of the same alignment bay and hook it up with the same equipment over and over again.

BTW zero toe goes against "performance" alignments, not surprised the prius uses that for economy.

I want to see you do that again....

Ha! No kidding. I'm always glad to be lucky than good.



Probably depends on the suspension and tire design as well. If the suspension is designed to not go toe in or out on acceleration or on static driving, the toe can be more zero. I'd bet that the low resistance tires have something to do with it too.

i think you got lucky when you put the bolt in. when i reinstalled the coilovers and caster/camber plates in my mustang after the shop that did the install messed it up, i eyeballed everything and threw it up on a Hunter laser alignment rack. everything was in the green except toe, and the only adjustments i did was to add more caster and camber to my liking and correct toe, i was giddy.

My best mechanical work is always done by 8% knowledge, 7% skill and 85% luck

You got lucky.
Not miraculous lucky, but let me tell you this won't happen often.