I would be interested in opinions on this short video - https://youtu.be/gJOkL6iOx5o
Thanks in advance
All I can say on the matter is, It doesn’t just affect 3 axle units, UK spec 2 axle units also do it or at least all the ones I have driven did, I will find out next time I drive our 14 plate 2 axle unit.
I did ask years ago about it, and apparently it has something to do with blocks placed between the axle and leaf spring being slightly different thicknesses, daft as it sounds, it does make sense for heavy vehicles to act this way, because if the driver was taken ill or fallen asleep at the wheel the vehicle will veer slowly off road and not into oncoming traffic, thankfully 
As for it causing driver fatigue, and never noticed a difference in tyre wear on the front axle, that’s more BS than I have just posted if its not true!!!
Probably left hookers pull to the right when driving on the right and go in a straight line when driven over here, iv’e no idea.
Oh, and it doesn’t just affect Scanias.
Thats right weeto - on a 4x2 unit it is just the weight of the steering box piston. (which adds about 500g / 1lb to the steering wheel force) The axle packing blocks have a little effect but they do affect the tyre wear. I moved mine to the n/s 3 years ago as tipping the truck towards the kerb seemed crazy. Scania could not disagree.
LHD and RHD hold a straight line when driven abroad and both pull left over here as they are set up almost the same. Just the steer axle is rotated 180 deg on RHD for the wheel camber and that is why the axle packing blocks are on the wrong side.
All vehicles working predominantly in the UK will pull to the left eventually. It’s all to do with the road camber; roads are generally higher at the crown and gently taper down to the verges (all to do with water run off I’m told) so consequently in the UK you are constantly correcting the steering to the right by a minuscule amount. Eventually as the vehicle ages you get a tiny amount of free play in the steering assembly which would result in the vehicle turning to the left if no steering input was present.
As Weeto correctly hypothesised (guess who ate a dictionary for brekky?) a vehicle operating predominantly in mainland Europe would consequently pull to the right naturally. I imagine that if you drove a vehicle where it’s operation was 50/50 UK and abroad it would have completely neutral steering traits.
Hi maoster, I’ve actually been looking a new vehicles pulling left but the situation you describe should be accounted for by wheel camber and/or caster settings.
Take a look at this 1 min demonstration youtu.be/XlFRyyzp6-8
I did used to drive a left ■■■■■■ 4x2 FH a few years, we got it from new, in the UK the steering wheel used to be at angle when running on a straight road, but in Europe it sat nearly straight. Can’t say either situation caused me any extra fatigue.
However I have noticed the videos are posted on You Tube by Neutral Steer UK, who it seems having identified this problem, (that nobody here seemed to be bothered about), amazingly enough have got a solution to it, which I’m sure for a small fee they’ll be willing to share with you. 
Neutral Steer UK has developed a new after-market solution to rectify the problem of left drift, which affects a number of trucks in the UK when cruising in a straight line.
muckles:
I did used to drive a left ■■■■■■ 4x2 FH a few years, we got it from new, in the UK the steering wheel used to be at angle when running on a straight road, but in Europe it sat nearly straight. Can’t say either situation caused me any extra fatigue.However I have noticed the videos are posted on You Tube by Neutral Steer UK, who it seems having identified this problem, (that nobody here seemed to be bothered about), amazingly enough have got a solution to it, which I’m sure for a small fee they’ll be willing to share with you.
Neutral Steer UK has developed a new after-market solution to rectify the problem of left drift, which affects a number of trucks in the UK when cruising in a straight line.
i’m sorry, but there solution appears to be some weights bolted to a draglink… if the manufacturers thought it was a real problem, im sure they would of thought of this.
i wonder if the new volvo fh/fm with the volvo dynamic steering has this issue?
also, i believe fiat tuned the steering on some of there cars to drift to the kerb side should a driver fall ill etc at the wheel.
Volvo probably suffers from this problem the least muckles - but the steering force on a Scania to correct right can be up to 2 kg (4.5 lbs). Not that much maybe but all day long everyday can cause fatigue and injury to hand, wrist and back – and yes nobody does seem to be bothered about it but maybe because they never thought there was a fault or a solution.
Sometimes the best ideas can be the simplest philgor – and the manufacturers have either been unaware of this problem or they consider they have got away with it as it only affects the UK – but I guess the cat is out of the bag now. The dynamic steering will overcome the problem but I doubt if you could retro fit.
There is only a prototype at the moment but hopefully a market product will follow.
If Fiat deliberately made the cars drift left what would happen if one of them was involved in an accident and it hit a bridge or a vehicle on the hard shoulder? Of course trucks drifting left on the motorway are a serious problem for vehicles on the hard shoulder.
Not exactly a new phenomenon, vehicles have run down the camber, with or without power steering, and suffered from shoulder wear for many years. Nor is it unique to vehicles with steering boxes and drop arms, rack and pinion steering has none of these parts fitted yet it still displays the same symptoms. Have they actually got out of the cab and used a spirit level on the road? I very much doubt whether there are many sections of road anywhere which are perfectly level for significant distances. If the road surface is perfectly level then there is going to be a problem with surface water drainage. If you place a ball on even an extremely gentle slope it will run down it.
I might be persuaded there was something in it if the video showed the steering slowly rotating onto lock if the vehicle vehicle was supported level on axle stands, and had the engine running.
cav551:
Not exactly a new phenomenon, vehicles have run down the camber, with or without power steering, and suffered from shoulder wear for many years. Nor is it unique to vehicles with steering boxes and drop arms, rack and pinion steering has none of these parts fitted yet it still displays the same symptoms. Have they actually got out of the cab and used a spirit level on the road? I very much doubt whether there are many sections of road anywhere which are perfectly level for significant distances. If the road surface is perfectly level then there is going to be a problem with surface water drainage. If you place a ball on even an extremely gentle slope it will run down it.I might be persuaded there was something in it if the video showed the steering slowly rotating onto lock if the vehicle vehicle was supported level on axle stands, and had the engine running.
Road camber and drift has been measured - and you may notice yourself when you are driving (if your tyres aren’t worn) your truck holds a better line on sections of the road that have a right camber.
Too much friction on a static set up to actually see the steering wheel rotate but this is the closest to the type of test you mention cav551 https://youtu.be/XlFRyyzp6-8
The last 4 series I worked on had the auxiliary steering linkage on the n/s of the chassis and I never noticed whether there are easily accessible test points to determine PAS system pressures, but an accurate large scale test gauge ought to reveal interesting data.
cav551:
The last 4 series I worked on had the auxiliary steering linkage on the n/s of the chassis and I never noticed whether there are easily accessible test points to determine PAS system pressures, but an accurate large scale test gauge ought to reveal interesting data.
This is unaffected by PAS pressure cav551
something good:
This is unaffected by PAS pressure
But you are saying that it is.
Video 1 Quote: “…Torsion valve opens …gives a powered input to the steering system…”
and Quote: “…this gives a left turn force to the steering system which can make the torsion valve open more often”
When the torsion valve opens hydraulic pressure increases. The video of the spring balance attached to the wheel only proves that it takes more effort to rotate the stub axle about the kingpin and the linkage and the ball joints in that direction, plus if in circuit, to force the flow of the operating fluid through the system in that direction. The difference in spring balance readings may have nothing whatsoever to do with the propounded theory. The vectors of the linkage make sense, but you have not so far proved that the torsion valve opens and gives a powered input to the steering system
Hi cav - the torsion valve opens and gives powered input when it doesn’t need to because of the left bias in the system but this would happen whatever the fluid pressure was (unless it was zero 
- The torsion valve starts to open at approx 500g force on the steering wheel
The PAS is disconnected in that demo video to eliminate any hydraulic forces - it is only demonstrating the imbalance in the steering rack caused by the drag link. The main ‘left turn force’ that needs to be overcome for use in the UK.
As I understood initially the theory is that the steering linkage design introduces a left turn force. This may also be exacerbated in a vertical installation of the steering box by the weight of piston inside the box. Fair enough I am not arguing with that. However the theory goes on further to say that these forces cause the torsion valve; the hydraulic direction control valve for simpler understanding; to open and initiate a powered left turn force. If indeed this latter is happening, then an hydraulic test gauge should show it and prove the theory. Without evidence to prove that there is hydraulic assistance to the mechanically induced left turn force, then that part remains only a theory.
I am being pedantic about this because I believe that if a powered left turn force is proven to be present, then this is a matter to report to Vosa technical as requiring investigation, and a possible vehicle safety recall campaign by the manufacturers. For official notice to be taken of the theory then more supporting evidence is likely to be needed. Any required rectification would be at the manufacturers’ expense, and not require an aftermarket bolt-on solution at cost to the operator.
This may all be true and a similar solution to the problem be required, in which case than a patent application should be instigated .
Hi cav. . yes thats right except its not
to open and initiate a powered left turn force
but these effects cause the driver to correct right with a powered right turn force.
You may notice when you are driving; you correct right then release, correct right then release etc - so, generally most of the time the wheels are being powered to the right and then being allowed to centre under their own forces. I believe this is one of the reasons for the asymmetric tyre wear some vehicles suffer where the n/s outer edge and the o/s inner edge wears.
The manufacturers and VOSA are not interested but it has been cleared by the VCA - By coincidence the patent is published today.