Steering wheel not self-centering

[NICAT]

Hi Friends.
I have a 2002 Mercedes-Benz W163 ML320. I previously started a thread about the car being very tiring to drive. There are several contributing factors, but one of them is that the steering feels quite heavy, which is common for this model.
However, a friend drove it yesterday and said that it is not just heaviness. The steering wheel also does not return to center properly after turning.

From what I think, self-centering is not directly related to power steering performance, so I am trying to identify what actually causes the steering to return to center and what could reduce or eliminate that effect.

The car is running relatively wide/high-profile tires (255/65R16 29PSI ). Could tire profile or pressure contribute to poor self-centering, or should I focus more on suspension geometry or steering components?

I would also like to understand the underlying theory, so that in the future when i test drive a new car to buy, if i experience such issue I can know whether this behavior is model-specific or caused by a correctable issue.

 

[BrendanC]

i would flush power steering system and check air pressure then inspect front end components. alignment is a big factor in tires returning to straight. if you have worn out parts which is likely with the age of the vehicle, alignment could be wonky.

 

[Sequoiasoon]

When I had my Sequoia there was a member on the forum that owned a Tundra. He happened to be a software engineer for Hunter Alignment Systems. He recommended top end of the "range" for caster with toe and camber at an exact#. Many complained about feeling unstable prior but his numbers fixed that. They were all in factory range, you just had to find a shop/tech that would do it. He actually recommended even slightly higher on Caster but that would be an individual relationship with your shop/tech. His settings mine was great for the life of the vehicle, great tire wear, stable, re-center nice.

My daughters '08 CRV had an issue with the steering rack that just wouldn't re-center, barely. Took a long time to figure out, my shop found it basically by accident. If your last bigger turn was to the right it would have a drift to the right. Last big turn left, it would drift left. Tiring as anything on drives. All suspension was good, bushing solid, alignment spot on, tires moved for radial pull tests, weighted driver checked etc. Came down to the rack issue, they changed it and totally transformed the highway driving experience in a good way. Whatever was worn on it was crazy. Shop had never seen that prior either.

 

[The_Jeff]

Are your tires and rims stock? Rim offset also affects wheel re-centering.

 

[D60]

I think in simple terms return to center is a tiny bit of toe-in and plenty of caster. Beyond that, a steering box or rack that's excessively worn (and thus tight) can cause this. Probably nearly seized ball joints, too.

I'd be curious about alignment specs.

 

[NICAT]

Approxmately 35mm reduced offset. But i think i had such issue even with stock wheels. Anyway, the car has different wheels out of factory, each with different offset.
But steering system is weak point of those models.

 

[The_Jeff]

When you crank the wheel hard you'll see the tire lean, that's caster at work. And it leans on its corner. If you mess with the rim offset you move the center of where the car puts its weight on the tread patch relative to the upper ball joint/ strut mount and it's no bueno.

 

[NICAT]

When you crank the wheel hard you'll see the tire lean, that's caster at work. And it leans on its corner. If you mess with the rim offset you move the center of where the car puts its weight on the tread patch relative to the upper ball joint/ strut mount and it's no bueno.

That makes me feel great that you guys at this forum can visualize everything and explain the physics behind it
Normally i had hard time explaining mechanics nearby that why oversized tire cause wrong speed readings

By the way, can having high-profile, tall sidewall tires, reduced pressure (as in my case), which are structurally less rigid than low-profile tires, reduce the effectiveness of self-centering due to caster?

 

[JavierH19]

That makes me feel great that you guys at this forum can visualize everything and explain the physics behind it
Normally i had hard time explaining mechanics nearby that why oversized tire cause wrong speed readings

By the way, can having high-profile, tall sidewall tires, reduced pressure (as in my case), which are structurally less rigid than low-profile tires, reduce the effectiveness of self-centering due to caster?

No zero effect to my knowledge. I've never seen a case like that.

 

[D60]

First, I don't have much experience with passenger cars but on trucks (both SFA and IFS) it takes A LOT of additional offset (aka minimal backspacing) to do much to return-to-center.

I've run 2" wheel spacers and wheels with 2.5" backspacing (which is so unheard of they were custom built) and while it can cause a poor ride, vibrations and absolutely screws with scrub radius, I never saw any noticeable impact on return to center.

But again, these are trucks and not finely tuned sporty cars. Still, I'd put wheels down the list. I suspect something else is going on. Furthermore, wheels will require a parts cannon while alignment might just require twisting a few fasteners.

 

[JimPghPA]

Get it aligned with some place that has a Hunter brand 4 wheel alignment macheine. They are very accurate. And even only one back wheel slightly out of alignment can show up as the steering-wheel requiring the driver to input some constant turn force on the steering-wheel.

 

[DavesVette]

I had the same issue on a Crown Vic, and it was a badly worn ball joint on one side. Replaced it and problem solved.

 

[Aichiguy]

Pump them up to 35 psi and test drive it.

 

[Mainia]

When I had my Sequoia there was a member on the forum that owned a Tundra. He happened to be a software engineer for Hunter Alignment Systems. He recommended top end of the "range" for caster with toe and camber at an exact#. Many complained about feeling unstable prior but his numbers fixed that. They were all in factory range, you just had to find a shop/tech that would do it. He actually recommended even slightly higher on Caster but that would be an individual relationship with your shop/tech. His settings mine was great for the life of the vehicle, great tire wear, stable, re-center nice.

My daughters '08 CRV had an issue with the steering rack that just wouldn't re-center, barely. Took a long time to figure out, my shop found it basically by accident. If your last bigger turn was to the right it would have a drift to the right. Last big turn left, it would drift left. Tiring as anything on drives. All suspension was good, bushing solid, alignment spot on, tires moved for radial pull tests, weighted driver checked etc. Came down to the rack issue, they changed it and totally transformed the highway driving experience in a good way. Whatever was worn on it was crazy. Shop had never seen that prior either.

You find a tire/alignment/general service shop with a alignment rack that do work on tuner cars ( street racers/autocrossers). They have zero issue with YOU dictating the "exact" alignment spec and they will hit it exactly. with no crying. If you don't know what you want, they will get you setup with what works. Most likely the first try. Most alignment shops just get in between a LARGE "dirty" swing that is almost is a "anything and everything is in spec"

 

[Donald]

Check front end suspension if that's tights then check steering box.

 

[JackWildfeuer]

It could be a bad rag joint/intermediate shaft. Think about the part that goes through the floor/fire wall. It could be ball joints, inner or outer tie rod ends.

When did Daimler go to drive by wire?