What causes steering to self-center? - Page 3 - PeachParts Mercedes-Benz Forum

leathermang · #31 11-07-2008, 02:20 PM

Back to my point about the super market cart wheels with respect to this example...
They do the same thing even in reverse...

Will your car wheels ' self center' in reverse ?

Seems like I have seen some funny videos of police trying to get to the keys of a run away car going in circles in a parking lot.... but only in reverse... thus the supermarket cart wheels are not in the category we are speaking of...

Number_Cruncher · #32 11-07-2008, 02:23 PM

Yes, it is exactly the same effect - the vital difference being the wheels on a supermarket trolley have unlimeted steer angle, while a car's wheels hit the end stops.

cscmc1 · #33 11-10-2008, 12:31 PM

Quote:

Originally Posted by Number_Cruncher

For the OP, I would jack the car up, and temporarily disconnect the inner track rod ends. Then, try to swivel the wheels by hand - if, for example, you have a ball joint which is seizing up, this could hinder self centreing action. By disconnecting the inner, you can also assess the friction levels in the outer track rod ends using a similar method.

Dumb question, but -- how "freely" should the ball joints move? I did a little tinkering over the weekend and found that the wheels will swivel, but not terribly easily. I know "not terribly easily" isn't a very specific term, but I'm not sure how else to put it. The wheel was off the hub, and I was able to swivel it with some effort by just grasping the rotor. I would think that the car ought to be able to overcome that in order to self-center, no?

I did discover that one tie rod end has a torn boot, so the exercise was not in vain. I have something to replace!

Number_Cruncher · #34 11-10-2008, 03:29 PM

>>I did discover that one tie rod end has a torn boot

If that track rod end is full of rust and is binding, that could very well be the problem. I would be tempted to fit a new track rod end rather than just replacing the boot.

cscmc1 · #35 11-10-2008, 03:36 PM

Quote:

Originally Posted by Number_Cruncher

>>I did discover that one tie rod end has a torn boot

If that track rod end is full of rust and is binding, that could very well be the problem. I would be tempted to fit a new track rod end rather than just replacing the boot.

I'm sorry, yes, I meant that I'll be replacing the entire end. It looks to be relatively new, but for the work involved, it makes more sense to just replace the whole end. I may just do both sides since I will be needing an alignment anyway.

Thanks again!

t walgamuth · #36 11-10-2008, 07:56 PM

I'm not sure the alignment specs for a 210 are the same as for a 124.

If it does not have enough caster it will not center up correctly. Stiff ball joints or too tight steering box or stiff tie rod ends could also do it.

Tom W

cscmc1 · #37 11-10-2008, 08:45 PM

Quote:

Originally Posted by t walgamuth

I'm not sure the alignment specs for a 210 are the same as for a 124.

If it does not have enough caster it will not center up correctly. Stiff ball joints or too tight steering box or stiff tie rod ends could also do it.

Tom W

Thanks, Tom. I looked at the specs and toe/camber/caster are all very close if not the same. The "after" specs I have are all within the margin of error, anyway.

I am still working on this... I am going to loosen the steering box a bit more this week and see how it feels.

awsrock · #38 11-10-2008, 09:53 PM

Quote:

Originally Posted by leathermang

Seems like I have seen some funny videos of police trying to get to the keys of a run away car going in circles in a parking lot.... but only in reverse... thus the supermarket cart wheels are not in the category we are speaking of...

My step Dad had to jump into a car that was doing that once..he said the woman was just standing there screaming,

Hope you figure your problem out!

Scott98 · #39 11-10-2008, 09:59 PM

For positve castor, think about a bicycle which has positive castor. You can take your hands off the wheel and it will still go straight. Now imagine that you induced negative castor, brought the wheel closer and closer to you. It would be much harder to get it to self center. Getting castor right on these cars is nowhere near as critical as camber and toe. Castor doesn't really affect tire wear, just the car's ability to self center for the most part.

Scott

t walgamuth · #40 11-10-2008, 10:24 PM

MOre castor also helps cornering speed. As the car loads up the suspension in a turn the caster turns into negative camber and keeps the tire perpendicular to the road.

Race cars have a lot of it normally.

And mercedes benzes.

It also makes a car track nice and straight on the highway, but on a heavily cambered road it will make the car pull toward the ditch.

Scott98 · #41 11-10-2008, 10:31 PM

Quote:

Originally Posted by t walgamuth

It also makes a car track nice and straight on the highway, but on a heavily cambered road it will make the car pull toward the ditch.

You could also induce more positive castor on the passenger's side to help overcome the tendency to pull on a heavily cambered road.

I don't disagree with anything you said but I don't consider my 67hp 240 a race car so I'm not too concerned with castor as long as it is in the ball park range and my car tracks straight.

Scott

turbobenz · #42 11-10-2008, 10:40 PM

toe in is very critical. when I got the alignment done I went for a test drive with the mechanic and it wouldnt center at all out of a turn, infact it turned itself! this was from the toe being slightly off

cscmc1 · #43 11-25-2008, 02:41 PM

As a follow-up: I replaced the tie rod assemblies (L&R) in anticipation of an eventual alignment (figured it would be a good idea since I'm going to have to pay for the alignment either way), and I am sure I threw the toe off at least a bit. Nevertheless, the car still does not self-center, but will try to do so when backing out of my driveway (???). Maybe I have enough toe OUT at this point that the car sees "toe in" when reversing and tried to center the wheels? I am still not sure why the car wouldn't self-center when it was last aligned, with toe in-spec.

A proper alignment will have to wait, as I am headed out for a military deployment for a few weeks soon. Just wanted to bump this thread back up; thanks again for all the thoughtful replies!