Power Steering Rack Centering How critical ?

[alcyon]

So recently I swapped my front subframe bushings and had to remove the steering rack. When i put it back on the steering wheel was towards the right when the car is going straight. So i removed the steering wheel and turned it one notch on the spline, and its just a tiny bit to the right. I got a full alignment 2 weeks ago, and I noticed the car now had a tendency to pull left after a while. So I was wondering about toyota's hydraulic P.S system. as far as i know, even if the rack is not centered correctly, if the wheels are aligned correctly, with the steering wheel untouched, the torsion bar inside the rack shouldnt be twisting, so it shouldnt be sending any more fluid towards the other side. Is my problem a purely alignment problem, or it's a must to center the rack as best as I could. I would think not centering the rack properly would cause uneven full lock travel, that should be it.
The alignment guy suggested increasing left caster and reducing right caster, he says this is happening because of road crowning. Car is RHD and I live in a RHD country.

 

[Enraged]

The alignment shop should have fixed everything so that the wheel is centered when the rack is centered. If they didn't, I'd take it back and get them to fix it.

 

[Asterix]

Yea, centering the steering wheel should have been part of the alignment. If it pulls to one side under power, maybe they didn't get the thrust angle set to 0 like it should be. It seems unlikely that things are out of whack enough that the power steering is trying to pull the steering off straight.

Could be the road crown doesn't help. Try driving around a large parking lot and see what happens. There's no crown in a parking lot.

All that said, I've had more bad alignments over the years than good ones. Good ones take time and skill, which is lacking at most shops.

 

[alcyon]

Yea, centering the steering wheel should have been part of the alignment. If it pulls to one side under power, maybe they didn't get the thrust angle set to 0 like it should be. It seems unlikely that things are out of whack enough that the power steering is trying to pull the steering off straight.

Could be the road crown doesn't help. Try driving around a large parking lot and see what happens. There's no crown in a parking lot.

All that said, I've had more bad alignments over the years than good ones. Good ones take time and skill, which is lacking at most shops.

Could explain what is this thrust angle ?

 

[Asterix]

In a rear-drive car, the rear suspension should be aligned to the centerline of the car so the net thrust from both tires pushing the car forward is aligned with the axis. If it's not aligned, the car will tend to steer to one side. It's most obvious when accelerating, but will show itself while holding speed because there is constant thrust even so.

Did you get a report with your alignment that shows before and after measurements?

 

[SupraTrbo89]

Also, you don't need to remove the steering wheel to adjust it. You can simply disconnect the input shaft where it goes into the rack, straighten the steering wheel and reconnect the input shaft.

 

[destrux]

The rack center is important because if the tie rods aren't the same length then each side of the car will have different bump steer effects side to side and you'll get a pull when hitting bumps or dips in the road. The alignment procedure in the TSRM has a check for this right after initial toe check, I think the max difference they list side to side is 1.5mm of thread difference.

If you look at your tie rod adjuster threads and there isn't about the same amount of exposed threads on each side then the rack isn't centered. A thread or two difference is ok.

The alignment shop shouldn't ignore this check, but a lot of them do. It's not reasonable to expect them to fix it with a normal alignment fee but they should let you know about it and that they'd have to pull the steering shaft or wheel to recenter the rack for an additional charge.

That thing about setting a car up for road crown is not all roads are crowned the same, and where I live not many are center crowned. They're usually sloped the entire way across both lanes to one side, so crown will be different depending which direction you're traveling. On top of that most of them are also tire rutted from heavy truck traffic sinking the pavement which negates any effect on steering that the crown had in the first place. With tire rutted roads you will get random pulling no matter what, especially on wide tire cars, because you can't predict how the car will sit in the ruts. So when I do alignments at work I do them with even caster and even camber. I set them up with as much front toe in as I can, within the OE spec range ( on my MKIII I use 0.10 degrees overall front, 0.30 overall rear) for better high speed stability on rutted roads. This setup works well for me. Turn in is still quick despite not being an agressive toe-out setup. Some really rutted roads will pull to one side or the other, it's unavoidable, but on a fresh new flat highway the car goes straight without touching the wheel.