knocking/jump on full lock

[lightyears]

Hi guys, I have a small issue which has arisen on my 850, when turning on full lock to the right the car feels like its jumping over itself and knocks, before I get out in the snow, is there anything obvious which can cause this? the steering of late has felt a little vague when turning again to the right.

[cyclogenesis]

My first guess would be worn wishbone bushes. Mine is doing the same thing on LHS.

[Derek UK]

Is the lock stop missing?

[Alpine]

there is an engine mount on the lower right hand (driver's side) side of the car, could be that. Mine knocked on full lock, and I changed it and its been ok since.

[Juular]

Mine has always done that, changing the wishbones didn't help. A friend's S70 does the same.

I think it's fairly normal, especially on cold frosty or gravelly ground.

You haven't seen wheels skipping on full lock till you've tried a 200 series, again totally normal.

[cyclogenesis]

I would caution against saying that it is normal. Steering should be precise and not wander. except under hard driving when torque steer can occur especially with some makes of tyre.

There are a number of things that can cause such things but the skipping that Lightyears mentions is likely to be one of the following.

Wishbone bushes
Balljoint
Inner or outer track rod ends
Subframe mounts

If none of these have been changed over the last 5-10 years, then changing just one, is unlikely to remedy the situation.

[capt jack]

This can be normal under some circumstances. it's all to do with Ackermann steering geometry and the need for the two steered wheels of a car to turn in different radii.

I can sort-of grasp the science, but if you want to dig deeper then try Professor Google!

Basically the path taken by the wheel is so tight that under some circumstances it will simply skip across the road surface.

From a practical perspective, things that can contribute to this skipping are

• a poor surface - the OP mentioned snow
• cold tyres - the walls are stiffer and less likely to flex
• worn tread - less grip
• turning on a gradient - where the suspension geometry changes - for example on a ramped driveway entrance

My 1997 S90 is very prone to this, especially on cold days when reversing out of our driveway. The NSF front tyre - which happens to be more worn that the OSF, older and a different brand, will "skip" quite noisily.

On warmer days, or when the tyre is well warmed up it won't do it.

Apparently Mercs and Lexus cars do it too, and it's nice to think that they are in good company!

Of course, the caveat is that like those other two makes, the S90 is a RWD drive car with an impressively tight turning circle, and I'm not sure how far it's true of FWD cars, which have less acute turning circles and I guess, different geometry.

On an 850 it'll definitely be worth checking for the presence or otherwise of a (well-greased) steering stop, as these too can cause odd noises if they dry up and fall off - which they can do quite easily.

The other thing to check is tyre pressure. Incorrectly inflated tyres exhibit incorrect behaviour!

And yes, I think that 240s will be prone to this. Very tight turning circle and relatively narrow wheels - so the geometry and the reduced grip are setting it all up nicely.

Jack

[lightyears]

Thank you all for the various pointers, ive temporaryly taken the 850 off the road for a full inspection, I was planning to renew pretty much all the front wheel components anyhow and this have given me a good excuse to do it earlier

[Shinsplintz 101]

Take a quick check of the cv joint at the end of the drive shafts, ensure they are free moving and well packed with grease. Sometimes they can bind up on full lock if dry/damaged.

[amazondean]

Originally Posted by Shinsplintz 101

Take a quick check of the cv joint at the end of the drive shafts, ensure they are free moving and well packed with grease. Sometimes they can bind up on full lock if dry/damaged.

I have to agree that it does sound like a cv joint. Unfortunately they can be difficult to diagnose when checking the wheels manually, as they tend to only show up as a fault on full lock and under load. That's when the bearings have the least amount of contact in the race! They only have to be worn a small amount for the ball bearings to slop around slightly in the joint causing a slight clonking noise as they turn.