Modifying Power Steering Pump Valve - Page 2 - PeachParts Mercedes-Benz Forum

matsalleh76 · #16 06-25-2010, 01:43 AM

Irregardless of comments on arm strength this query needs serious technical investigation.

There are many of us that feel that Merc steering is a bit too heavy and, to be honest, Merc steering feedback is not the greatest either.

We wanted to lighten the steering on our 2.3-16 and assuming that a PS pump pressure increase would lighten it up we replaced the factory 95bar pump with a new 110bar PS pump. Result: zero. No effect.

We have researched the data/literature we can find and can not locate anything on what controls (for lack of a better word) steering "boost."

Based on our experience with the 110bar pump we assume that:
1) there is a pressure limiting valve somewhere in the system that controls boost;
2) the PS pump rating is the maximum pressure the pump will deliver to the system;
3)if the system only requires say, 80bar to develop its valved boost then any increase in PS pump pressure is bypassed back to the reservior.

If these assumptions are correct the boost/pressure control valving must be in the steering box.

Now, where are the valves? How to access them? And finally, how adjust system working pressure (with shims or spring changes) to utilize more pump pressure to increase boost?

Yes, any proposed increase in system pressure will load up the steering box seals but I am willing to give it a try. I am retired and have the time and facilities to do the job.....and, if need be, un-do it if it doesn't work right.

Serious technical comments, references/links to data sources/diagrams will be greatly appreciated.

Thanks & regards,
bobf

tilac1 · #17 06-25-2010, 04:58 AM

Well said and very thoughtful Bob. I understand the 'sportline' option on 300E cars included along with suspension upgrades, etc, a quicker ratio steering box but I don't know if it had more 'boost'. I believe the sportline cars had different alignment specs but I don't think the standard alignment specs changed over the years for the 300E. The theory that more caster in early cars could explain a few things about the steering as well. Thanks for the input re the pump, you've saved me $$$ and time.

So it would seem it's either the steering box and/or the valving inside it or the caster settings. I too very much want improved steering.

matsalleh76 · #18 06-25-2010, 10:03 AM

Larry, you are correct: you run what you brung; personal preference determines what you drive, and how well you like operating it but we are all different, have different tolerance thresholds, etc. and one size does not necessarily fit all.

But part of the joy of playing with cars is choice: you choose what fits you best and after analysis, may choose to alter something to improve the fit.

After running everything from a Bugatti, Ferraris, various 6 & 8cly Alfas, a Stutz, etc. we wanted an everyday pre-computer sports sedan. We chose the 2.3-16 because it did what we wanted very well. But after a time it was evident there were areas that with a little thought, could be improved.....if we chose to do so.

The gear change was one. The manual Merc gear change arrangement is poorly engineered: long soft rubber bushed flappy rods connecting the gear shift to the gearbox change levers. It was a bit loose & vague. Of course we could and did drive it that way but compared to the rest of the driving experience it was not "nice" so we chose to see if it could be improved.

An hour on the lathe with some nylon bar stock, a few circlips, nothing radical, and we had a gear change that snicked crisply through the gears. Made a very good driver's car better.

Merc power steering on the 2.3-16 is great. The 2.3-16 has the fastest Merc steering ratio and is a joy. We just happen to like light steering so tried to lighten it up with a pump change. It did not accomplish anything, but if it had lightened the steering it, like the gear change, would have increased our driving satisfaction.

Now for the real reason for entering this thread: we have a 124 230TE automatic wagon. It has the slowest Merc steering ratio and only needs pegs around the big Merc steering wheel to qualify as a barge but we love it: great quality, dead reliable, and the best workhorse in the garage.

But we have chosen an area needing a bit of improvement: lighter steering will make keeping it between the buoys less of a chore. Alignment and steering component condition are not part of the problem: camber/ /caster/toe are all to spec and the steering bits & ball joints are all A-1.

We have established that changing to a higher rated PS pump will not lighten the steering. We and judging from the posts in this thread others, need to know if it is possible to lighten the steering with some work on the pressure valving in the steering box.

Please lets have some technical imput. That is what this forum is for. MBDoc?

Thanks & regards,
bobf.

babymog · #19 06-25-2010, 12:13 PM

"good road feel" and heavy steering are not necessarily mutual. A good system can have both, as I beilieve that all but one of us would like.

I've got an alignment shop next-door, I'll ask if they will look up the alignment specs on the '95 and the '87 so that I can compare/post them.

dpetryk · #20 06-25-2010, 12:29 PM

I think this thread should concentrate on the issue of what it takes to modify the steering system to give the owner the feel he is looking for. Weather we are "whimps" or not is irrelevant. Those issues fall into the category of personal preference and opinions. Nobody will ever see it the same way. We could all argue till the cows come home and never agree. Lets not go there.

Now lets talk about how to change the feel of the steering.

If you understand how the power assist works it would be obvious that changing the pump to one that has a higher pressure rating or more flow will not affect the feel of the steering. Because the pump is not where its at. In fact this has been confirmed by one members experience doing just that. The business end of the "steering feel" lies in how the valves are reacting to the input of the steering wheel and the load that the steering box has to move.

There are two springs in the valve body that have a huge effect on the feel. I know because I had one break and the steering was hugely affected. I never tried to modify the springs but I believe that changing the springs or weakening / shortening them would give one more "power" to the steering box for a given input.

These two springs hold the valve shuttle centered where there is no hydraulic assist applied. When you turn the wheel, you begin to compress a spring which allows the valve to open in one direction or the other. When the valve opens, hydraulic oil pressure is applied to the rack on one side or the other and that oil pressure is what does the heavy work moving the rack and thus rotating the pinion gear.

Try shortening the springs and give it a try. I'll bet a $100 bill that your steering will get easier.

babymog · #21 06-25-2010, 12:34 PM

Lowering the threshold via the springs should IMO increase boost at low speed/high effort steering, not at higher speeds. This is how the car has a "variable assist" feature, as it should only limit the amount of effort necessary to drive the hydraulics. Opinions?

matsalleh76 · #22 06-25-2010, 12:48 PM

dpetryk,

Thank you for the response.
I will pull a spare steering box from the pile and investigate a spring change. I will post the results.

Cheers,
bobf

Stretch · #23 06-25-2010, 01:12 PM

Before you all go ripping out steering boxes is it not worthwhile looking the castor angle of the suspension set up? From what I understand about this is that you can trade straight line stability (or a bit of it anyway) for a more flickable feel. Would that do?

I guess this is only really appropriate for speeds above say 15 mph - as you'll need the wheels to be turning to feel the effect I guess. Or do you all feel the steering is too heavy at a standstill?

dpetryk · #24 06-25-2010, 04:50 PM

IIRC you don't have to disassemble the steering box. The valve bits are all held in with a C clip. You might even be able to do it on the car if you have access to it. I just cannot recall if it is acessable. I think it is on my 126's. Just not sure.

If you look at this DIY;

http://www.davidpetryk.net/Mercedes/Steering.htm

Line item #8 is a shot of one side of the valve. #29 is the opposite end.

Another shot #51.

tilac1 · #25 06-25-2010, 08:52 PM

This is getting very interesting. I think our friends are on the right track. Great DIY primer David, thanks. I'm willing to try shortening or weakening the springs you describe if I can get at them on a W124 without too much grief.

dpetryk · #26 06-25-2010, 09:56 PM

I am very interested in the results you get.

Stretch · #27 06-26-2010, 03:18 PM

Quote:

Originally Posted by LarryBible

I doubt that changing the pump would effect steering effort. I expect that there is a relief valve that regulates pressure, not the pump.

There is indeed a relief valve - but it is there for a reason. Adjust with caution!

Stretch · #28 06-27-2010, 07:07 AM

Oh yes and on my w123 Vickers Type 24 pump (top mounted on the engine so different from yours) the relief valve consists of a simple plunger and a spring. There is only a single O ring sealing it. I guess all pressure relief valves will be about the same.

Anyway you could measure the stiffness of this spring by applying a weights to the top of it and measuring the deflection. The deflection should be linear until the spirals start to touch. To calculate stiffness you need to divide the applied force (weight X force due to gravity {g}) by deflection. In SI units stiffness k = F / x

It is best to calculate the stiffness (k) because that is how stiffer or softer springs will be sold. This is good information to have...

You could then measure the radius (or diameter) of the surface of the pressure relief valve to calculate the area. You now need to estimate the distance required for the spring to travel for the valve to crack open. It probably won't be much. Plugging this estimation into the equation given above. The opening Force acting against the spring when the valve is cracked open is k / x.

From this you can calculate the pressure at which the valve will open.

Pressure (P) = Force (F => found from k/x see above) / area of piston / relief valve.

If there is a way of measuring the pressure at which the relief valve opens then it would be good to compare this with your theory!

pawoSD · #29 06-27-2010, 08:35 AM

I think the issue here is that someone needs to work out a little more, not modify their steering system.

"Heavy steering" means weak arms!

tilac1 · #30 06-28-2010, 05:24 AM

'There are many of us that feel that Merc steering is a bit too heavy and, to be honest, Merc steering feedback is not the greatest either.'

=molasses. Steering quality, not about arm strength...