Questions regarding the pusuit of clearer steering signal...

[Lago Blue]

The 'signal' analogy is this: the tauter the length of string between two empty tin cans, the better you can both send and receive subtle messages from one end to the other.

From the official Audi 7A 20v Service Training Manual, I was intrigued to read the following about our power steering pump:

"The pump has a flow-limiting valve, which will reduce the pressure supplied to the steering gear as engine speed increases. This is to improve road feel at higher vehicle speeds."



Particularly as this was written prior to and not referring to a servotronic rack (IIUC, also developed to vary the steering's power-assist, but with vehicle speed: from ZF's own official history (I've added the underline) "Servo assistance diminished with higher speeds, thus increasing steering rigidity – and therefore also steering precision."). Least that was its' intent. Later versions pursue the same end.

You may recognize increased steering component train rigidity as a desired target characteristic, as I've have previously posted regarding this being outlined in academic automotive engineering papers; and it is also why the Arm-Stops mod (an oft presumed suspension only mod) improves steering response, by preventing fore / aft free-play in the steering fulcrum chassis mounts; a.k.a. the front axles' OEM A-arm bushes. Similarly, as steering train slack is removed, rigidity is therefore added, response quickens, and the immediate transmission of pure signal to and from the driver, because in this case the steering pivot-points are held more solidly, is improved.

Below are two pages from a much older complete and very thorough official Audi Power Steering Training Manual (1977), found at the quite extensive and interesting type 85 site: KVquattro.com), along with the excellent colour illustrations and explanations of the rack's interplay of mechanical and hydraulic functionality (even the relief valves opening pressure range is listed), is an illustration of the above particular flow-limiting valve design feature.



http://kvquattro.com/powerSteeringManual.html

So, a question that might emerge would be (and perhaps best answered by Error404), could an earlier UrQ hydraulic vane pump (or at least its' flow valve and/or its' pump housing's restriction particulars) perhaps be unique, and offer a little less assist at higher engine speeds, and perhaps explain the apparent steering feel difference between that car and those which followed? Alex, looking back, is your pump housing mod to fit your adjustable flow-valve and/or an alternate effective flow-valve spring length something still worth pursuing today?

[PRY4SNO]

Interesting post, as always.

It does make me wonder if it might just be more simple -- if not specifically easier -- to install a quicker ratio OEM steering rack that brings the 2.9 turns to lock down to 2.3?

[Lago Blue]

Hi Dustin,

I read that a rack swap might never be simple, and dread the necessity to have to find out. There was a good rack ratio discussion which starts here (link below) in Alex's thread on a project that may have eclipsed the pump mod above.

https://www.s2forum.com/forum/techni...784#post898784

[Error404]

I have been a bit slack in recent years on my quest to “fix” the steering. For sure the modified pinion torsion bar was the biggest improvement. The documentation is lying a little as the early pumps don’t have a pressure reducing flow control valve, the valve is sprung which in theory closes with higher shaft speed but effectively only limits the flow rather than reducing it, so the flow rate is around the same as at low rpm / parking speed.

I machined my pump rear housing to accept a sprung flow control valve from a Porsche 968 which uses the same passive reduction, doesn’t really make a noticeable difference, I even played around with the size of the flow orifice but couldn’t find much improvement. Sooner or later you drop off a cliff and the pump can’t keep up with demand.

Fundamentally it is a geometry problem, coupled with a sloppy chassis and a big fat engine & gearbox hanging over the front axle. There is very little castor and virtually no mechanical trail, roll centres are very “safe” and the bump steer is, well…comedic.

I have designed some front uprights and revised front ball joints / wishbones to solve some of these issues hbut in recent years not had the time or inclination to do anything about it. The proper solution as Audi recognised in later years is to move the steering rack and push the engine & gearbox back as far as you can.

[Lago Blue]

Hi Alex,

Thanks for that descriptive update putting all that in perspective sir. I sincerely hope you don't give up on 'the old barge'. If it was some sort of civilized Group B car, and needed nothing, what experimental fun could you have, and you might struggle more to offer much to improve it! I hardly think you've been loafing.