What causes steering to self-center? - Page 2 - PeachParts Mercedes-Benz Forum

cscmc1 · #16 11-06-2008, 11:17 AM

Quote:

Originally Posted by leathermang

Ok... search for this using my screen name... I know there are some threads which Larry Bible and I put up some good info...
Basically you need to understand that no matter what they print out... if everything in your steering and suspension system is not correct they are pretty much " getting it as close as they can " and sending you out the door with respect to the toe in....
During a summer break from college I worked in a front end shop.. first half as a mechanic and the second have as ' service writer/ parking the cars in the stalls'... LOL...
The guy that did the alignments was old and cranky... but for some reason liked me... I asked a lot of questions and watched him closely. It was also a tactile education being able to drive a whole lot of cars which needed work from the front around through some pot holes and then into the back of the shop... getting to ' feel ' that was very interesting.
If you can't find them hollar...

Thanks -- I'll search using your forum name. I appreciate all the help. The problem I'm having is that the car sometimes wants to change direction when it hits cracks or other deviations in the road surface, and correcting that change in direction often seems leads to an over-correction, if that makes any sense. I have replaced many parts up front (or at least checked them -- many had been recently replaced by the p.o.), and several links and subframe bushings in the rear chasing this issue.

When the car is tracking straight, it feels great. It just gets a little squirrelly when it wanders and I try to correct it.

leathermang · #17 11-06-2008, 11:23 AM

You are describing the classic symptoms of worn steering / suspension parts...
Remember that the height of the car affects the steering settings.... that is why I suggested the new springs " as a matter of principle" as the FSM says so often....
Springs have a much shorter ' life span' than most people think.... I am not going to post it because I will get a bunch of flack... but the height your car is supposed to be is listed in the FSM... so you can measure it... it all has to be right to have any chance of the toe in staying correct during all the things a suspension needs to do....

cscmc1 · #18 11-06-2008, 11:28 AM

Quote:

Originally Posted by leathermang

You are describing the classic symptoms of worn steering / suspension parts...
Remember that the height of the car affects the steering settings.... that is why I suggested the new springs " as a matter of principle" as the FSM says so often....
Springs have a much shorter ' life span' than most people think.... I am not going to post it because I will get a bunch of flack... but the height your car is supposed to be is listed in the FSM... so you can measure it... it all has to be right to have any chance of the toe in staying correct during all the things a suspension needs to do....

Height is one component I have not checked, and my car has 245K miles on the odo. Wouldn't surprise me one bit if the springs were original. Thanks again...

leathermang · #19 11-06-2008, 11:43 AM

Mileage certainly makes a difference... but for metal fatigue even just sitting with the springs compressed ( the normal condition for a car ) for decades can take it out of specs...
They are reasonably priced compared to some other stuff... and no way around replacing them unless you have a local heat treatment shop close...but much safer to use the stock springs from MB ....

cscmc1 · #20 11-06-2008, 11:46 AM

Quote:

Originally Posted by leathermang

Mileage certainly makes a difference... but for metal fatigue even just sitting with the springs compressed ( the normal condition for a car ) for decades can take it out of specs...
They are reasonably priced compared to some other stuff... and no way around replacing them unless you have a local heat treatment shop close...but much safer to use the stock springs from MB ....

Sounds like a logical thing to check anyway. Thanks!

leathermang · #21 11-06-2008, 11:53 AM

It is very important... and usually ignored ....

lutzTD · #22 11-06-2008, 09:34 PM

Quote:

Originally Posted by cscmc1

Mine are a bit wider, but it did the same thing with the previous (stock) size tires. Does yours not center at all now?

it centered perfectly with my previous ones. now it get close but is usually off to one side or the other depending on which way it is returnng.

winmutt · #23 11-07-2008, 07:59 AM

Quote:

Originally Posted by lutzTD

it centered perfectly with my previous ones. now it get close but is usually off to one side or the other depending on which way it is returnng.

Thats pretty much what I have as well. I assumed it was time for a pump rebuild. Happened like this before and after alignment.

#24 11-07-2008, 08:10 AM

Quote:

Originally Posted by tangofox007

Positive caster, with a little help from the idler arm bushing.

Right. Its the same idea that keeps shopping cart wheels following the path you want the cart to go.

cscmc1 · #25 11-07-2008, 08:50 AM

Thanks for all the input; I'll try to update this thread when/if I get the issue resolved!

leathermang · #26 11-07-2008, 09:43 AM

Quote:

Originally Posted by ForcedInduction

Right. Its the same idea that keeps shopping cart wheels following the path you want the cart to go.

It probably would not hurt anything for someone to have that image as an impression of positive camber... but technically I do not think that applies.
The pivoting axis is vertical to the rolling surface...or you have great trouble turning... and the axis for the wheel is 90 degrees to that axis but offset...and following....
If you keep that relationship and apply it to the front of a bicycle you could not balance on it... I saw something on PBS showing people trying to ride on made that way....

Number_Cruncher · #27 11-07-2008, 11:49 AM

>>but technically I do not think that applies.

For a 4 wheeled vehicle, you can implement castor with a vertical swivel axis and/or a tilted swivel axis. As long as the projection of the swivel axis on the road surface is ahead of the centre of the contact patch, there will be self centring action.

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.

leathermang · #28 11-07-2008, 12:07 PM

Quote:

Originally Posted by Number_Cruncher

>>but technically I do not think that applies. -- Greg
For a 4 wheeled vehicle, you can implement castor with a vertical swivel axis and/or a tilted swivel axis.

If the claim is that that is one example of positive camber...in this discussion of SELF centering ability.... you can see that a supermarket basket wheel has no self centering ability because it is simply a follower of the forces placed on the upper part of the basket....
It has a ' passive reaction centering' ( or following ) ability only.
Greg

Phil · #29 11-07-2008, 01:03 PM

This post reminded me of a site I had seen before so I started looking and found it. This is info that is good to read even if you are having work done by a shop just so you can understand what they are talking about.
http://www.familycar.com/alignment.htm

Number_Cruncher · #30 11-07-2008, 01:57 PM

>>is simply a follower of the forces Yes, but on a car, that amounts to being a self-centreing action. To see this, probably the best way is to draw out the force vectors acting at the contact patch. In a car (not a bike), whether you choose to implement trail by moving the "king-pin" axis forward, or tilting it, as long as the projection of the swivel axis is ahead of the contact patch, you get self-centreing action.