Forged front control arm upgrade - AudiWorld Forums

Forged front control arm upgrade

Old 05-17-2012, 11:20 AM
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Default ...and an upgrade to augment OEM A-arm bushings

Why consider these two mods, and why do them together?

IMHO unrestrained, OEM A-arm bushings fail prematurely due to excessive fore-aft movement. As this is a too often required routine maintenance ritual, why not install some preventative measures to lengthen the service interval and add a performance benefit? Further, since they likely already require replacement anyhow, why not also leverage the opportunity and prep for an upgrade in advance, by getting some forged A-arms ready in advance, to do the swap? Recently I did this simple upgrade to my early B3 Coupe. Yes, there is a caution in the Bentley against mixing front suspension parts from the early and late cars; and that is exactly what I have done, so sue me.

Notes on parts used:

- Forged A-arms (I used late Coupe items but I assume B4 ones would work as well?). After blasting, treated 3 times with Naval Jelly, sprayed acid etch primer and brushed on Tremclad, avoiding the bores for the bushings;
- B4 ball-joints (I wanted to avoid confusing the parts man with a request for the late B3 items, which I assume are identical?). P/Ns: 893-407-365-E; & 893-407-366-E. Note that the 3-bolt ball-joints from the stamped steel arms "appear" to work/fit, but not really. The true made for forged A-arm ball-joints are effectively taller, maybe stronger, may have a slightly different effective position of the joint and do allow more camber adjustment. The proper ball-joints allow the wheels to be set closer to vertical which I much prefer. My coupe has an effective ride height approx. 25mm below OEM, so this is perhaps more critical than otherwise;
- B4 Nuts, ball-joint attachment to A-arm studs: N -902-856-02. This is the flanged style lock-nut (with the large OD integral washer built in), it may have been the subject of a note in the Bentley or a TSB?
- B4 A-arm bushings (same part ordering reason & assumption as ball-joints above). Installation was done in a heavy bench vice; &
- Thrust-washers, anti-friction. Caution, habit forming. Installed on the front face of the forward bushing and the rear face of the aft bushing. I am on my Mk III's now, having upgraded the material each time, I now whittle them from Acetron® GP. These are the items which provide the preventative benifit.

Bushing installation cautions:

- Do not attempt to squeeze the arm's two trunnions at once in a press as bent arms will result. Best to use a vice and treat each trunnion singly.
- Although it is possible to displace the centre core of the new bushings fully flush with the face of the outer core during installation into the arm, either on the one end or the other, I strongly recommend that you take steps to avoid such in either case. I used some appropriate tubing and an outer race from a dis-assembled wheel bearing which has a rubber friendly diameter and profile for this purpose.

Beyond that the forged arms are stronger items, one must also use the larger control arm bushings. These larger OD bushings also have a larger metal core outside diameter. What this means is, not only is the volume of rubber greater than the smaller bushes, but the total area of rubber bonded to the shell and core is also larger and therefore stronger. Multiply those increased areas in a single bush times the four bushings required per axle, to understand the net effect.

Where that increased strength should be felt is in the bushings installed fore-aft resistance to displacement. Surprisingly to me however, was the realization that even the bigger bushed arms move significantly. The extent of this movement, particularly towards the rear (during braking; and certainly upon wheel/tire impact of any significance such as a pot-hole) was evidenced as follows. Because several years ago on my B4, I spray-painted the arms with new OEM bushings already installed; re-installed the arms, and shortly thereafter noticed that in use, the paint had been worn off the rear rubber face of the bushings. The brand-new bushing's rubber-faced flanges were hitting the sub-frame brackets!

So even that these larger bushings are theoretically more resistant, I made some travel-limiting thrust-washers to prevent the fore-aft movement I was seeing evidence of. I'm very happy with the resultant driving feel and improved bushing longevity. I therefore now have simply duplicated that set-up on my Coupe.

Last edited by Lago Blue; 09-17-2015 at 10:26 AM. Reason: clarity and content
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Old 05-17-2012, 03:50 PM
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Originally Posted by Lago Blue View Post
Why consider this mod?

IMHO unrestrained, A-arm bushings fail prematurely due to excessive fore-aft movement. Since they require replacement, why not prep for an upgrade in advance by getting some forged arms ready to do the swap?

Beyond that these forgings are stronger items, one also must use the larger control arm bushings. These larger OD bushings also have a larger core diameter. What this means is the total area of rubber bonded to the core is larger and therefore stronger. Multiply that increased area times the four bushings to understand the net effect.

Where that strength can be felt is in the bushings installed fore-aft resistance. How I realized that even the big bushing arms move significantly towards the rear during braking is because I spray painted the arms with new bushings installed and shortly thereafer noticed the paint wore off the rear rubber face of the bushing.

So even that these larger bushings are theoretically more resistant, I made some travel limiters to prevent the fore-aft travel I was seeing. I'm very happy with the result.
I'm not sure if i understand you....

few other options:
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Old 05-18-2012, 09:01 AM
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Default What I like about the OEM elastomeric bushings & forged A-arms...

Good point Varia, I will go back and re-write the previous post. I was in a hurry yesterday and just wanted to get the post outline started. There are options to every mod to consider and each has its cost/benefit. I want a mod to be reliable, effective, invisible and inexpensive. I believe these mostly OEM items achieve that.

I think the OEM elastomeric (E/M) bushings can be made to work extremely well here to mount the A-arms to our cars. As the working environment for these is rather severe, I like the fact that they are a sealed unit and have no "moving" parts. When I say work extremely well, I mean better than as originally installed when installed correctly according to the manual i.e. with the weight on the wheels prior to fixing. This improvement has been my experience with the simple addition of relatively low cost thrust-washers.

Even a set of new smaller OEM E/M bushings can make for a very satisfyingly firm yet low-maintenance suspension mounting with the addition of decent thrust-washers. More firm than stock and longer life-ed.

I think the higher internal volume of the larger OEM E/M bushings can work even better. In use, the motion of the A-arm causes the rubber in the bushing to heat up. More volume means any heat will be less concentrated. If your OEM bushings are degraded, when driven they will "feel" better cold; and worse as they warm up. If your OEM bushings are degraded, steering wheel vibration is more likely; and a re-balance of your wheels can only partially mask it for a little while.

If your OEM bushings are removed from the two inboard mountings for inspection, you may see evidence of degradation such as one or both of the centre cores have taken a set and no longer point directly fore-aft, and/or the core or mid-brace are displaced from their original fore-aft stepped positions. This can occur before more obvious tearing of the rubber or loosening of the cores. On a given A-arm one bushing usually fails faster than the other, usually the aft bushing fails first. Once one has begun to fail, the other is immediately overloaded and the process accelerates.

What the Thrust-washers do:

By simply denying the bushings most of their previously available fore-aft travel space; and as their remaining job description is now more focused down to just having to accommodate rotation of the arm, the inherent strength and original integrity of new OEM bushings can be greatly preserved.

Driving with Thrust-washers:

Here is my theory as to why the car feels better to drive with the thrust-washers installed. On receiving an aft-directed force from the A-arm such as when the wheel assembly encounters a bump, the rubber rear face of the aft bushing, already in contact with the thrust-washer backed up by the sub-frame, cannot really move aft. Previously, without the thrust-washers, it could. The suspension is now forced upward immediately, rather than waiting for the suspension to first move aft. As the total mass of the spinning wheel/tire/brake rotor/outer C/V, drive-shaft and hub/caliper assembly have now a more vertical trajectory during each deflection, there is less fore-aft momentum generated that must be dispersed by that arm's two bushings alone. Previously, this was in part transferred to the sub-frame and beyond. Furthermore, since there is little to no aft movement and momentum to be absorbed, there is also no re-bound forward, back to the start position either. Now such impacts are immediately directed to items better able to dissipate their effects; the spring and damper. I think this is both the missing behaviour that makes the ride feel better; and the reason that the NVH is <i>not</i> worse despite a now more direct path for NVH transmission to take place!

As the OEM bushings are more confined than originally allowed, they heat up less, they tear less, they simply stay new longer. Also, your alignment settings are better preserved, your two strut axis remain more parallel, steering response is more immediate and precise; and suspension inputs are felt less as steering wheel feed-back.

In use, I can't tell the difference between Bilstein Sports and HD's, but I can tell if there are thrust-washers.

I also really like the OEM forged A-arms not just because they are awesomely strong, but because they are relatively cheap (when found used), elegant (almost delicate), and they hold paint well! They are also simply one piece of steel.

034 makes some very nice items and I have no experience with the alternatives you list. They may have a net benefit I am unaware of however to my eye some of the things I dislike about these type of A-arms are as follows:

- the use of self-aligning bearings where there is no requirement for that capability;
- the bearings total working surface area must be quite small therefore the wear rate must be high;
- the bearing is open to the elements; &
- some of the load paths will put the spherical's threaded shank in bending and in shear.
-there may be perfectly good reasons to be able to adjust the distance between the inner pivot points and the main A-arm body independently; but for my purposes, I just can't think of any.

One last argument in praise of OEM equipment such as these forged arms and bushings. They are stock on the famous rs2. Audi hired Porsche to re-engineer (and build?) these, HP and torque where multiplied, many parts where replaced, but not these two.

That I can find at the wreckers service-able forged arms to replace the original welded sheet steel assemblies, that I can blast, etch and paint them to an as new condition; and that were purposely designed to allow the fitment of my old style anti-roll bar (despite which perhaps never occurred on a production model?) adds job satisfaction to a necessary task and appeals to my D-I-Y nature.

Last edited by Lago Blue; 09-17-2015 at 11:03 AM.
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Old 05-21-2012, 07:02 AM
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Any pictures of the thrust washers for those of us who are less familar with them and their use?
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Old 05-25-2012, 08:40 PM
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Originally Posted by Harzley View Post
Any pictures of the thrust washers for those of us who are less familar with them and their use?

I have VAP bushings to go in my car... but my wifes is going to get all new OEM bushings this summer and I would like to add these "washers" when I am in there.
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Old 05-26-2012, 01:24 AM
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Default Re: Any pictures...

Ok I'll work on that. However, I have a black sub-frame carrying black control arms, black OEM A-arm bushings and black "stop" or thrust-washers...

Meanwhile basically where you have air between your A-arm bushings fore and aft rubber faced ends (when installed into the front of; and the rear of the A-arm); and the sub-frame brackets which secure them; I have filled that space with not entirely inexpensive stiff slippery and now more durable plastic.

Note how the metal center-core protrudes from the outer shell's flanged face (and as shown in the photo below, from the other side of each bushing as well). As far as fore-aft movement is concerned, that equal core protrusion on either end of the bushing is indicative of a fully relaxed and centered bushing that is in brand new condition. But in driving, that center cannot hold. Left alone in use but detached from the sub-frame for inspection, one will find with time that the cores become increasingly displaced and misaligned off axis from the shell's center-line; and worse.

The core's overall length represents the available space in between the two sub-frame brackets that "fix" the static bushing core in space. Looking at one end of the bushing, the amount that the outer shell is shorter than the core illustrates how much movement must be taking place from the bushing's relaxed/centered position before the face contacts the sub-frame bracket.

This is where I think bushing self-destruction begins. Because the sub-frame surface is not entirely square to the bushing face; that rubber is not particularly slippery; and that the bushing's contact with the aft bracket occurs in a small area, the rubber face of the bushing is eventually torn from the flange; at that spot. As soon as that happens, the detached rubber is pushed out of the way more and more during every subsequent similar action. Now the available room for bushing deflection fore-aft expands; and over-extension of the bushing rubber accelerates. Soon the bushing cannot re-center itself after deflection as it becomes increasingly torn from itself, the core, mid-brace and shell.

The rubber-faced flange of the outer metal shell wants to move back and forth along the center-line of the bolt-hole with every suspension input. The installed stop-washer against the rubber face, makes the now largely rotating only A-arm effectively as space filling as the fixed center-core. Therefore very little A-arm fore-aft movement can occur, the rubber on the faces will compress somewhat, so some small amount of movement still must take place. However, the rubber bushing faces are in full and constant contact with the stop-washers; and now rotational movement takes place largely between the washer and sub-frame brackets, so single point wear of the rubber faced shell flange is reduced entirely. The trade-off is that the washer becomes the wear item. Hence the need for the fancy plastic. However, in return this reduced range of fore/aft motion allows the bushing rubber to remain more fully bonded longer, it keeps it's memory longer and returns to the neutral position more accurately for much longer than otherwise. Increased driving pleasure and longer service intervals will result from this mod.

Luxus e-mail me and perhaps I can thrust some stop-washers into your hands. But you have to promise me that they won't sit on the shelf like VAP's Mount-Savers did till your strut-mount tops caved in!
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Last edited by Lago Blue; 11-10-2015 at 02:54 PM. Reason: I just had more to say.
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Old 05-29-2012, 06:44 AM
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I'd be interested in buying a set of the washers or at least getting some specs to have them made up myself. I can't make any guarentee they won't sit on my shelf, but would like to have them available when I get to replacing the control arm bushings. It is inevitable at this point, but have some other projects keeping the Audi as the primary driver.

Do you think using thrust washers in the rear would be helfpul too?
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Old 05-29-2012, 11:37 AM
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So basically, you are filling in the gap around the steel insert? What type of material are you making the washers out of?

Do you have any pictures of the early bar bolted into the late arms?

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Old 06-01-2012, 10:43 PM
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Default To Harzley & 90QC...

If your interested, e-mail me for further details. Harzley yes, on a B3q (your car, yes?) the same behaviour I described above also happens at the rear. 90QC, good idea for a photo, I'll get one of that too. If by steel insert you mean the central-core of the bushing that the attaching stretch-bolt goes directly through, then yes; no more uncontrolled air-space for the control-arm to fly around in.

Last edited by Lago Blue; 11-10-2015 at 02:54 PM.
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