PAS weight adjustment?

[Madmac666]

Hi all, I'm hoping some of you knowledgeable MB gurus can answer this question...

I turned my 2020 Sprinter 319 4x4 into a motorhome but the one thing that I struggle to live with is how heavy the steering is compared to other W907 vans I've driven. The dealer says the 4x4 versions are all like this and it may be adjustable, but they couldn't say how it is adjusted.

The steering wheel is fairly slippery and the steering is so heavy that it makes roundabouts difficult. We all know that the sprinter can be steered around quickly with one palm but this is impossible because it's so heavy. I literally have to keep a tight grip on the wheel to turn it safely.

It's not like it's only slightly heavier than the 2wd vans, it's much heavier. It's still definitely power assisted though

Does anyone know how it can be adjusted? Is it a pressure valve on the pump or rack? Different pump or rack? Software controlled?

It's doing my head in and spoiling the driving experience. I want to lighten it up, even just a little

Thanks in advance

 

[Bellow]

Does anyone know how it can be adjusted? Is it a pressure valve on the pump or rack? Different pump or rack? Software controlled?

What little knowledge I have here is from the GMT400 platform but as it's reasonable to expect all hydraulic PAS systems to operate from the same principles....
My GMT has speed sensitive PAS known as EVO (Electronic Variable Orifice). Its pressure relief valve has a variable sized orifice controlled from an ECU. Some dislike EVO and replace it with a 'delete kit'. AFAIK, the delete kit merely replaces the EVO valve with a fixed one where the stiffness of (or pre-load on) the spring and (fixed) orifice size dictates the level of steering assistance. An alternative to deleting EVO is to hack its wiring with a variable resistance resistor giving a selectable level of assistance from the dashboard. So far so GM - now MB.

Your Sprinter will have a pressure relief valve. On the GMTs it is on the pump. Yours probably is too but could be on the rack. If it's fixed (not variable) it won't have any electrical connections. If it is variable - the converse.
Your options would be to open up a fixed valve and reconfigure the spring stiffness/pre-load/orifice or source one already calibrated for more assistance. To replace a fixed valve with a variable one from another MB that has variable steering assistance and wire it along the lines of the wiring diagram below (for GMT400 EVO).

I'm surprised your steering is so heavy and possibly there is a fault either with the pressure relief valve or the load sensing. Another possibility would be blockage in the pipe/hose that returns fluid from the pressure relief valve spill to the reservoir - I'd check that. If yours is variable, then any fault in the wiring or the controlling ECU could be the cause of your problem.

Sorry I can't be more specific but the above (generalised as it is) should give you some ideas on which way to jump. Off the top of my head assuming zero faults, I suspect your best course of action is to source a pressure relief valve from an MB known to have lighter steering (2WD Sprinter?). Comparing part numbers of valves and pumps may help with that.

 

[Madmac666]

Thanks for your response. It's a mechanical system. I can't see any wiring going to the pump, but I haven't dug deep yet. If it's software variable then it should be easy enough to map it to be lighter. If it's mechanical then it may be easy enough to change the relief valve spring, pack the spring out etc.

It would be good to know how it's actually governed before I start taking it apart

It's been like this from new, and it only has 11k miles so I'm confident it's nothing faulty. As I said above, the dealer said all 4x4 sprinters have heavier steering than the rear wheel drive models. Whether that's because of the mechanical links in the rack and suspension, or just set differently by the factory, I don't know. I can't see the front driveshafts making it any heavier though, so I suspect it's set at the factory deliberately. I jacked the front up and the steering moves freely lock to lock from the road wheels so there's nothing tight mechanically.

If I move the steering wheel slowly, it's not that heavy, but try to move the wheel quickly (mini-roundabouts) then it stiffens up, almost like the flow rate of the fluid is too slow for the rack. My 2011 319 has a great feel and doesn't tighten if it's chucked round a junction in town quickly, for example.

My mapper is going to go through the factory ecu map to see if there's a setting for pump pressure meantime. He has a copy on file.

If I work it out, I'll post details here

 

[Petrol Pete]

Bellow has given you some great insight here, but my question is how could a MB dealer tell you that a 4 year old MB steers the same as a 1963 ERF bin lorry ?

You don't mention it but we assume you have replaced the power steering fluid (and filter) and the pump is running and delivering pressure to the rack ?

It's an odd one for sure , but for it to be that heavy at low speeds just does not sound right. I hope you sort it and let us know how you get on .

 

[Madmac666]

Pete,

I appreciate your input. To clarify, it's not so heavy you'd think it was faulty and it has been like this from new. It was the first thing I noticed when I collected it with 5 miles on the clock

To describe it better: on the 2wd Sprinter if you were stationary you could turn the wheel lock to Lock by placing your palm on the wheel and winding it quickly each way with confidence that your hsnd wouldnt slip off the wheel. On the 4x4 if you did that you'd need much more pressure and force, and it's likely your hand would just slip off the wheel.

It is noticeably heavier than all of the 2wd sprinters I've driven. It appears it just needs the pump pressure raised to match the 2wd models. The dealer said that all 4x4 are the same and assumed it was set to a different pressure at the factory, for what reason I can't fathom!

The van has larger wheels, but these never made any difference to the weight of the steering. The steering was heavier with the standard wheels and tyres than all our other 2wd vans.

I'm waiting on some info to come back from mercedes

 

[Tonye]

Hi, just a thought, it might have a steering damper, like a small shock absorber on one end, my old range rover had this to stop kick back when going off road. You say its easier when turned slowly so i suspect this is the case. On yer back pal and have a look. If it does have a damper fitted then i would try it with it removed if not going heavy off road. Best of luck.

 

[Madmac666]

Tonye, good shout. I've been underneath and can't see an external damper, but it could have something within the rack? That would make sense since it's 4wd and designed for off road terrain

I'm waiting info on part numbers for pump and rack between same model and age 2wd and 4wd vans to see if these parts are different, although I doubt I'll get info on the internal workings if each if they are different part numbers

I wonder if MB technical would be any help here