Announcement

**Lago Blue** · 25 April 2020, 14:22

Establish containment measures, eliminate unnecessary travel & return quickly to the home position, all proven low-tech preventative measures, themes that should sound familiar...

...if you remember me going on about this previously (and I certainly have!), and / or if you want to fix your A-arm bushes. And you should do.

Sorry, if you thought: "Ahhh! He's not gonna just repeat himself is he?" You'd be wrong. I think this just bears repeating, if a little differently.

This is about how to think about this mod (Arm-Stops), why the need, the fix, and the outcomes, etc. It asks you to consider this simple and inexpensive prescription for tactile driving improvements and the prevention of early failure in your necessarily next set of new Boge bushings (if their not NLA from the dealer already!).

This argues for, what results in, the use of a reinforced stock A-arm inner hinge attachment method that is much stronger and more durable than the stock arrangement alone. It's still a compliant mounting but stiffer axially and more heavily sprung to a centered home-position on that fore-aft axis while still allowing normal A-arm swing to take place, still unimpeded to any significant degree, just more precisely constrained, again axially.

A similar situation...

Consider this unrelated but literally parallel instance for a moment. Why is it so important that an alpine ski-boot be so totally connected to the ski, and why is that boot so inflexible laterally and tall? I think you'd agree that one of the main reasons has to be, to best enable instant communication between your brain and the snow to skiis interface. Further, the boots are so tall and unyielding, to allow your soft feet and lower extremities to better transmit clear and minute signal to and from the skiis, with some comfort; but immediately.

Why our steering can be such a dull subject...

Not unlike the above, excellent steering-response here (via the linkage between the road to tires interface and the driver's hands on the steering-wheel) is also all about the delivery of instant communication through what links those two ends. What works well must be high signal, low noise. Physical clearances or "play" in the connective linkage is dead-air time, a.k.a. "noise". It is noise because, as it has to be consumed before actual signal (both steering-wheel and tire contact-patch inputs) can be transmitted through to either end; it therefore blocks signal while that consumption takes place. Said noise is taken up by motion lost from signal, before the remaining signal can be sent. Further, as the now reduced signal is often left insufficient, more must be quickly added, usually resulting in over-shoot. Finally, as this fault (lack of more precise lateral guidance for the base of the steering axis) exists on both ends of an axle, a wheel on one side of the car, can and will be doing either more or less proper steering than the opposite side, and here's the thing; or randomly anything in between. All these inaccuracies are cumulative; and make steering dull. B2 & 3 Q's with similar arms on the back will also have some inadvertent and random rear-steer if not tended to. As found, mine certainly did.

Q: How is it that an improved mounting of a suspension arm's mounting bushing could possibly help steering response?

Perhaps seldom recognized as such, but since the A-arms alone fix in position the ball-joints (the bottom pivot-points of your two steering axis) laterally, all three of each arm's joints must share in that fixing. Therefore, and maybe even less obvious or understood, the arms' to sub-frame hinged attachments (via the bushings), are a key part of the steering linkage, precisely because the ball joints are half the fulcrums around which the wheels steer (you can guess the other half of them and why this mod compliments Strut-Stops so well!). Somewhat like us currently, our A-arms need best be better confined to a central home position in order to prevent certain harm. In this case harm to the bushes' service-life, and perhaps more importantly to an enthusiast, to their best possible resilient performance, the degradation of which also acts to the detriment of both basic wheel alignment and tire wear, besides steering feel, accuracy and stability under braking. If one was as fussy over the condition of the the arm's rubber bushes as its' ball-joints (and you should be!), you'd have done this mod already.

The problem...

With stock bushes alone (without the mod), before long your A-arms first become increasingly less able to resist fore-aft displacement (much faster than what simple senescence would otherwise indicate) as just normal driving over-stresses bush cores by (almost) constantly stretching them first one way, then the other (axially) with every acceleration and braking action. This is their weak flank and this repetitive action quickly degrades them, With use, they accelerate towards total internal failure by over-heating, softening, un-bonding and/or tearing. This is not a bushing flaw, this is us not understanding the essential hopelessness of asking to both propel and stop the entire car even for a moment, let alone constantly, solely on the strength of those mere heat-adhered interfaces between the small rubber and steel rings hidden inside each bush. This is an error of omission or engineering! Of course they fail, and fail early (this is also why big bushes are better than smaller). The bushings are really pretty good at withstanding twist, and very good at resisting lateral force across their axis, but not good at resisting the endless push-pull of normal driving, along their axis. The mod relieves them of that task and the bushings' service lives extend forward dramatically (homeostasis). Problem solved. You can pretty much wash your hands of having to replace bushings with any frequency whatsoever thereafter.

Recognizing the issue...

Because the stock condition allows ever increasing amounts of fore-aft arm movement (up to about a quarter inch in total per wheel), requiring ever decreasing provocation and resulting in less self-centering afterwards, the arms are soon striking the sub-frame (at first, more so with aft-wards travel) regularly. This increasingly less restrained, random and independent for each wheel free-travel is a source of vagueness in the steering as explained above. If you had this play in the floor mountings of the driver's seat; it would drive you to you fix it immediately.

The fix...

In my view, in contrast with the stock condition, all unnecessary axial arm travel should and can be prevented. Your A-arms should not have to first travel to get to somewhere, where they then have something to lean on, before steering signal can be either sent or received to or from you. They already ought to be there, in constant contact for instant communication to take place.

Another quick parallel...

Like an ice-skate blade that has been properly hollow-ground to always be on an edge, even whilst changing direction, there need not be here a middle dead-zone between turning left and right; and like your soft foot in a skate's stiff boot...

Our axially weak stock bushings can be more effectively reinforced and restrained to allow only just the slight required primary design movement (here, strictly the arm's vertical arc of swing), without adding impactful friction, but in fact reducing it, and thus not allow any steering signal (via lateral ball-joint movement) to be lost. "Stops" improve the balance between capacity and load. Very interesting to me are the coincident yet contrasting benefits, in that both the bushing service-life and the strength with which it can hold the arm steady laterally, are each enhanced considerably over the stock condition without penalty to the other's effect; when the bushings' job-description is changed by this mod.

Symptom examples...

Photos below show typical early face-wear to bushings that indicate the arm's bushing faces already must have been both striking the inner faces of the sub-frame brackets, and rotating against them with some force; at the same time (think of the typical nose-dive that occurs while braking). The two rearward-facing bushings see the most wear first, as braking and the far edges of pot-holes are the dominant driving forces involved here, and because their impacts penetrate the most vulnerable fault-lines of our suspension (and steering) systems; with energy further focused precisely at and by it's weakened points. Despite not a lot of visible damage, all four bushes shown below will already be internally "marked" for early failure due to excessive axial displacement between their critical bonded central cores and outer shells. Evidence of this untoward movement and wear can be seen on your car in situ, by simply spray-painting the arm's fore and aft facing bushings largest face's white, and then checking how driving quickly wears that paint off the rubber. Or you can give the arm's a really good heave. This mod prevents that movement.

Mod outcomes...

That this simple and inexpensive mod also offers, beyond improved steering response, a very strong, durable and silent alternative to the stock bushing replacement routine, or to poly bushings, begs the question - why don't you already have your bushings restrained under lock-down in the home position to protect them from possible harm? Were you expecting them to develop herd immunity?

PPE for your bushings. Halt the bushing burn-rate. Ergo "Arm-Stops".

Audi A-arm bush face A.png Audi A-arm bush face B.png Audi A-arm bush face C.png Audi A-arm bush face D.png

Announcement

"Stops" aid A-arm Bushing Function

"Stops" aid A-arm Bushing Function

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