UrS4boy

This has been discussed this before. This is an attempt at pulling it all the C4 UrS strut bar info together with some new photos and a bit of cross reference to the B3/B4s. The impetus is the fact that yesterday I finally removed my stock 93 UrS4 strut bar and replaced it with a later style UrS6 strut bar. As a result, I had the opportunity to take some photos of the two bars side by side, discovering a couple of things along the way.

I first came across strut tower bars back in the mid-1980's when I competed in a local AutoCross ("slalom") series in a Jetta Mk1 that I had hot-rodded (I won my class locally in 1985). Back in those days, the VW chassis was not very stiff and under the stresses of AutoCross cornering, the OE strut towers would bend (slightly), changing the camber of that you had had so precisely set to -1.50 deg. Not good. The solution was to tie the two strut towers together. To quote Mr. Mojo from this forum, "the idea is to solidly tie the strut towers together so that turn-in loading is shared and dissipated more evenly throughout the unibody - body flex is thus minimized and suspension values remain more consistent, no matter how hard you push it." As a result, back in the day, there were many aftermarket strut tower bars for VWs available in the marketplace.

Flash forward to 1991 and the introduction of the 1992 UrS4 to the market place. Audi provided a fairlystiff chassis with a 28 mm front anti-sway bar as well as rear anti-sway bar but no strut tower bar.

Here is a photo of a pre-April 92 build UrS4 without a front strut tower bar or the brackets to mount one (Note the location of the yellow cap in the middle of the brake fluid reservoir):



Something must have happened (e.g. complaints or further testing) because near the end of the 1992 Model Year (MY), starting with UrS4s built sometime in mid-April 1992, the UrS4s started showing up with the two anti-sway bars *AND* a front strut tower bar. This bar was a rectangular tube that was bolted to new brackets that slipped over the strut towers. This bar was carried over to the 93 UrS4s and then to the 94 UrS4 and then the 95 UrS6.

Here is photo of the OE front strut bar in my 1993 UrS4. Note that in order to accommodate the new stress bar, the factory had to change the brake fluid reservoir from the 8E0611301 reservoir with the cap in the middle of the reservoir (see the photo above) to the 4A0611301E reservoir with the cap off set to the rear of the reservoir.



Here is a close-up of the left hand bracket and the mounting method (two hex head M8x35x1.25 bolts per side)


Base photo courtesy of zipdoa

In some cases with the late 92 cars, the strut tower brackets are NOT welded to the strut towers but are only held in place by the three bolts that hold the Macpherson front strut into the strut tower. Some people (e.g. quattropilot, fcarspec1) have been able to add the strut bar brackets to their early 92 MY cars by simply adding the brackets like that to their previously bracketless cars. Later cars,e.g. 93 and later, all have their brackets spot welded to the strut towers (probably a better idea).

That style of front strut tower bar remained until the 96 Model Year (95.5 in the US) when it was changed slightly. While the steel tubing stayed the same (dimensions and thickness), instead of ending with a square cut-off and a plastic plug, the ends were tapered and M8x20x1.25 Allen head bolts were used, set down into the tapered part.

Here is a photo of a 95.5 with the later style stress bar:


Photo courtesy of oliwer78

I am not sure why the change but Steve M. (boxflares) suggested that it was due to the close proximity of the hex-headed mounting bolts and the remote (+) battery post: "The bolts and washers on the early bar do their best to short jumper cables when you use the under-hood jump post. The later Allen head bolts are recessed in the cut-open end of the bar, so they don't interfere".

Steve also commented "I've modified the early bar to late style- very easy. Pull the plugs, use a Dremel to cut it down, and then a belt sander to smooth out the cuts. Some paint, and allen head fasteners, and you'd never know it didn't come that way from the factory."

Here is my car with a 97 UrS6 front strut bar mounted with "Stealth" black M8x20x1.25 Allen head bolts (all I could find - I inadvertently gave the OE allen heads to Koupecrazy awhile back)



There was some speculation that with the earlier bar having a PN of 8A0805645A, the later bar should have had a PN of 8A0805645B. Wrong. They are the same PN. Presumably, *IF* you found a new old stock strut bar now, it would be the new design and the PN would be 8A0805645A. Here is visual proof:





There was also some speculation (by me, before I found the new style bar) that the older style had thinner tubing walls than the newer style. Nope. Same outside dimensions and the same tubing wall thickness:



As a final C4 UrS note, the S6Plus V8 had a different design bar, using a round pipe, mounted to the same brackets as the AAN and V8 UrS4/S6s. The PN for the S6Plus bar is 4A0805755 which is not shared with any other Audi, even the V8 UrSs.


Photo courtesy of islingtonaudi (Doug)

Here is a detail of the end of the S6Plus bar (note the numerous spot welds used to hold the bracket to the strut tower):


Photo courtesy of islingtonaudi (Doug)

On to non-C4 UrS strut bars:

The 3B S2 coupes came with a strut tower bar. However, they were not square sections but round sections with crushed and drilled ends for mounting, as shown here:


Photo courtesy of s2stu via Martinjs and Error404

Here are the 3B PNs:



In a previous strut tower bar discussion thread, Skollie suggested that the strut tower bar PN, 8A0805645A, was the same for the B4 Audi 90. He was right, and more so, it also covers the RS2.



Here are the related B3 and B4 PNs (including RS2):

Item 12 - connecting pipe 8A0 805 645A
Item 12A - end plugs - 8A0 805 963 need 2
Item 13 - washer N 011 670 16 need 4
Item 14 - bolt ("screw, hex head") N 010 335 12, M8 x35 x 15 need 4

B3 and B4 90 (including RS2) brackets have similar but different PNs:
8A0 805 635B - Left
8A0 805 636B - Right

Here is skiguy's (CAANUCK’s) RS2 with the same early style strut bar (mounting brackets are different):



The square-ended 645A bar was used on the S2 coupe, the S2 Avant and RS2 until the end of the 1995 model year. In 96, the switch was made to the tapered-end bar. Although there is some conflicting info for the S2 coupe for 96, the consensus is they, like the 96 S2 Avant and the 96 RS2, received the tapered end 645A bar with the allen head bolts, as show in this photo (Note: polishing/chroming not OE)


Photo courtesy of Error404 and jasn11.

Here are the 1996 S2 avant and RS2 PNs showing the allen head bolts (this does not show for the 1996 S2 coupe some unknown reason):



Aftermarket:

For several reasons, e.g. the slotted mounting holes in the OE bars, lack of being able to preload the bar, Mance E. (VAP), came up with his own very precise design. He marketed these bars to both B4 and UrS people. I don't think they are available any longer:

Mance's (VAP's) solution



References(if you need to read more - don't respond there, the threads are past their due date)

Mr. Mojo's comments

Steve M's comments

Previous Strut Tower Bar PN discussion

A previous strut bar discussion thread started by me

GoHeels

Cool story on the evolution of our strut-brace Dave, and another way to identify the year. I'm glad Audi decided to add them, but I had no idea the early '92's didn't get them. Back in the day, I always thought it was a sign of a better performing car, and I don't think many cars had them outside of pricey sports cars.

The strut-brace is also a handy place to mount an EFI Express ignition kit. I've been resistant to drilling holes in my brace for the bracket I got from Marc last year, but after reading this I'll at least changeout the zip-ties this weekend, and perhaps add thin weatherstripping or felt pads in between.

UrS4boy

Thanks. Some of the 92s did get the square-ended bar. Just not the ones built before mid-April 92 (as far as I can tell). Years ago when there were UrS4s on the Audi lots, I was able to pin-point the build month (before or after April 92) just by looking under the hood (bar or no bar) and before confirming by looking at the door jamb sticker.

FWIW, the UrS6 tapered strut bar that I installed the other day had three holes in the vertical sides of the bar, seemingly from the factory. No idea why.