Steering coupler torque

[Gordon Watkins]

I've replaced the rubber steering coupler on my T6B Coupe and am wondering if the 4 nuts should be tightened to any particular torque or just enough to get the cotter pins installed? I can find nothing in the shop manual.

TIA,
Gordon Watkins

[Albert Tiedemann]

The thickness of the "flex disc" is equally imprtant.  You will find that there are two thickness that could be supplied for the application.  The original disc was a bonded fabric, round and 11 mm thick through the clamping surfaces.  It had "spool" pieces at the fastened intefaces for the nuts.  Actually, a VW part. Later versions were still round and 11 mm thick but now a molded elastomeric construction as above but the spool pieces had been supplanted by molded bosses and "most econimically formed" sheet metal tube spacers to limit the clamping distance.   The latrest "premium" flex discs now offefed by some purveyors are thicker by 2 mm, have squared off edges and embody a real tube spacer.  Molded construction with bosses as above. Just make sure you measured the one you have removed and, if different than the one you have removed, is longer then the steering wheel position will be effected and the calcelling mechanism may not work.  If visa versa, then an intial transverse distortion [step] will be prevailant in the flex disc.  Just how much that will effect longevity, I cannot say, but it is easy to remove the unwanted variable.  There is a flat milled on the steering shaft  that will accommodate some axial dispacement of the yoke clamp.  The through bolt will need to be loosened enough to spread the ears of the clamp and then retightened.  Sometimes it is easier to remove the bolt as this gives more acces to spread the ears.Now, having determined that the spacing is proper, the answer to your question about the torque on the through fasteners at 4 places is influenced by not only the need for a prvailing torque for axial clamping, but also resistance against rotation.  If you look on the head of the fasener, it may be stamped 8.8 or, if original, 8g.  The requisite clamping load for this size fastener with a coressponding grade 8 metric nut would equate to about 30-34 Nm.  I am not certain of the M8 DIN 935 castle nut grade used, but it might be 6S.  This would reduce the torque load considerably, and if 30-34 Nm were used, it would likely exceed the elastic limit of the threads and result in permanent thread stretch in the nut.  The castle nut alone is ineffective in maintaining any clamping load. Spring lockwashers, although used in the original assembly, are equally ineffective for the 8,8 grade fastener and would eventually loosen and fall off it not for the safety cotter pin.  The only acceptable locking element for use with the castle nut would be a serrated washer [Schnoor].  Conveniently, this is found to fit well under the head of a socket head cap screw and both are used in the 356C coupler assembly with the castle nut and the cotter pin. [the Germans, even though they conduct their own tests, rarely believe their own]I am certain that the original fasteners were very difficult to remove and the corrosive bond bodes well to keep things tight.  The only thing better from the get-go would be an anerobic compund--like locktite to name one brand.  Fasteners so treated have been shown to loose only 15% of the original tension[preload] in 75,000 cycles.If I were putting an original assembly together today, I would use the 8.8 grade fastener, the Schnorr washer, the castle nut and tighten to 15-18 lb-ft of torque.  This may be difficult to measure unless you use an offset adapter to the torque wrench.  And, don't forget the cotter pin.  The latter is your lifeline to keep the nut from falling off.  This was likely the Factory's reason/method to circumvent libility. If you can't wait for eventual corrosion to be your bond, apply some locktite at assembly.And as an advisement to all:There are replacement/alternate couplers out there for the very expensive factory version for the C car only.  Please see the article in the technical section of the 356 registry site.  All of these couplers use a prevailing torque locknut [acceptable with 8.8 fasteners]which promotes ease of assembly [no cotter pin to fiddle with], but they in themselves will eventually loose the reqisite tightness needed for the application.  Only one of these offerings provides the redundant safety that the factory included with the original coupler.  That coupler is the one offered by me [Afterwerke] that embodies an innovative safety tab of a sufficient thickness to prevent any anti-rotation of the nut that would produce looseness.  A ground strap with correct terminations and braided wire as original is also available from the latter.  No deliveries until May 10, 2008.Inquires off-line, please.