Diagnose light steering

[kilou]

Hi,

my Volvo S40 has always had a light steering but now this is really driving me crazy, especially on highway. The steering is excessively sensitive to road inclination and always pulls strongly to the side of the inclination (which means most of the time on the right). On straight line the steering really feel loose and light around center, especially on highway, but with speed it also vibrates sometimes. Driving the car is really not a pleasure, it's always about countersteering and adjusting. When driving to a stop light once, the road was slighty inclined on the left and the car pulled a lot to the left. If you remove the hands from the steering wheel it would turn for 1/4 circle just because of that pull!

I have checked and changed most of the parts:
- tire pressure OK
- alignment OK
- wheel balancing OK
- front lower arms (including balljoints) renewed
- tie rods/balljoints renewed
- front suspension (shock/springs) renewed
- strut top mounts renewed
- steering gear mounts OK
- steeing column OK
- steering gear pre-tension (tried several values, no change)
- Power steering OK
- every single bolt and nut has been tightened correctly and check at least 10 times the last couple of weeks. So basically the front suspension is almost brand new (the problem occured before renewing the parts as well so it is not due to the new parts)

I just came back from a test without power steering as I thought it could be the cause for this light steering as well. I disconnected the aux belt that drives the PS pump and drove the car like that. The steering was undoubtly very hard to turn but around center it always felt quite light. I think that the stiffer steering due to the lack of PS only occured at about 1/8 rotation in the steering wheel but around center I still get this wandering feel.

Now I guess the last thing may be the steering rack itself that could be worn out (the car is 260000km) but I can't understand that this would cause this behaviour. I for sure have a small play in the steering gear but about 5mm at the steering wheel only. This is still considered normal as far as I've heard. Moreover the weird thing is this extreme sensitivity to road curvature that pulls the steering and the car on one side. This makes the steering wheel turn so it is not just caused by play in the steering gear.

I would think it could be alignment but it's within specs. I have a small amount of neg camber and toe-in at front. I wonder if this could cause that behaviour on uneven or inclined roads. The only alignment setting that is slightly off is the right caster angle that is a bit less than the right one but it's still within spec.

Any idea what else I could try or test? I don't want to change the steering gear just to see that it wasn't the cause of the problem

 

[andyd]

Maybe apples and oranges, My 528e has a box, not a R+P, but the light feel was from a hair too much toe in

 

[punisher]

Caster angles are my first suspect in this situation, but if they are in spec, they are in spec. Does the vehicle have a variable assist system?

Maybe its tolerance stack. All of the variables (alignment, tire construction/pressure, rack)have added up to cause this concern.

Just throwin' it out there. It looks like you have done what you can to diagnose/fix it.

 

[kilou]

The caster angle is very small (stock is 2°.12' R/L and I have about 2°05' L and 1°80' R). Unfortunately this is not adjustable and I have no room to elongate the strut top mounts. This may explain a slight pull to the right but I get pull depending on road inclination mostly, and to the left too.

I don't have a variable assist system. The PS pump has a relief valve so that pressure delivered to the rack is constant but doesn't diminish woth speed.

I'm concern by the loosiness feel of the steering but about the vibrations as well, especially on high speed. Since the wheels are balanced and tires do not show significant degradation I can't understand where it could come from. Probabl that everything is related. I've seen that there is a small play in the lower arm front bushing. Actually the whole arm move slightly back and forth if I try to lever it with a screwdriver against the subframe. The bushing is OK bit it seems the subframe part where the lower arm is bolted on is slightly too large....but we're speaking about less than 1mm probably, it's very faint and I can't believe this could cause such a feel. I'll try to put a washer in there to see if it helps.

I'd love to increase (almost double) caster because 2° is nothing enough. The Volvo S40 started with 2° caster and the last MY (before current model) had 4° so I guess it was required. But as far as I remember my car wasn't as bad when new, it used to go straight with a "solid" feel even with its 2° stock caster angle.

 

[Gary Allan]

To little caster would mean ultralight steering ..but yours is in spec ..and as you said, not adjustable.

Just for the sake of sweeping out the unchecked corners, why not do a 360° rotation on the rack and reset the toe? I had to do this on my Peugeot. I had the advantage of no connections through the wheel ..so it was just removing a nut and recentering the wheel. That will put the pinion on a (mostly) unused portion of the rack. You may not have enough travel ..but it's worth checking out ...at least before you decide to swap it out as the last resort. For all anyone knows it could be some bushings that the rack floats on. The rack and pinion, themselves, are fine in a static stationary state, but move down the road and it may offer alternatives to how the wheels react.

 

[kilou]

Garry, from what I understand doing a 360° rotation on the rack and correcting for toe means that one tie rod is going to be much longer than the other. My concern is that this is going to create a massive bump steer because the tie rods inner pivots (inner balljoints) won't be at the vertical of the lower arm pivots. If the pivot points do not match while the suspension is depressed/compressed on bumps this creates bump steer which is a reall annoying feel. Moreover it seems I wouldn't have enough travel on the rack to do that.

I checked again more carefully every part. The lower arm bushings are OK but the small play I had seen is just the bushing itself slightly flexing (normal, less than 1mm). However I checked again the steering column and found some faint play in it. If I grab the lower coupling (the one that is bolted to the steering gear) with plyers there is approx 1mm free play at the steering wheel. This freeplay comes from the lower coupling itself and I cannot change that (the whole column must be renewed in case of free play).

I don't think that 1mm free play in the column is something to worry about and I don't think that this would cause such a bad steering feel. Probably the rack is worn as well but I have approx 1-1.5 cm free play at the steering wheel before the wheels are moving and this is the stack of column and rack free play. Usually I should have no more than 1 inch free play at the wheel so I'm not yet there.

I will try to put flat zero camber on front wheel and possibly 0 toe-in as well. Unfortunately my car doesn't have any steering dampener, probably this would help a lot to prevent steering from pulling according to road inclination. But it seems not straightforward to install one DIY....

Do ou know if there is any "ugly home-made fix" I can do to lower the play at the column lower coupling?

 

[kilou]

When I wrote "steering column lower coupling" I meant the universal joints. There are 2 U-joints on my steering column and the lower one (which also act as the coupling) has most of the play (but approx 1mm at the steering wheel only).