Cobras have Halibrand pin-drive knockoffs in which the knockoff spinner seems to sit flat against the wheel hub face. This might make it more likely to loosen as it doesn't have the cone-type seating of the Rudge-Whitworth design. Halibrands may not self-tighten as the Rudges do, therefore the safety wire is more necessary than on our cars where it would seem to be redundant.
The custom wheels Ted Halibrand’s company made for multiple types of street and race applications utilizing a center locking nut, wing nut or hex nut, were made with female tapers for a center lock nut with a male taper to wedge into. I cannot discuss all the different cars and applications but I do have some Cobra experience.
The stock Cobra arrangement was Rudge-Whitworth “spline drive” with different thread directions for the different sides of the car as usual. With the stock arrangement the normal issue to how much effort and how large a hammer it takes to get them loose even with generous use of anti-seize compound on splines, threads, and tapers at last installation. To me the term spline drive seems misleading because the clamping compression created by the center lock nut between tapers holds the wheel pretty firmly.
The so called “pin drive” arrangement favored by Ted Halibrand is for sure a misnomer as the pins his company supplied were very soft mild carbon steel and were not strong enough to do much but resist wheel slip on the hub during center lock nut installation or removal.
So why have some Cobras had trouble keeping wheels tight? There are so many variables that an in depth coverage in a forum thread would not be practical. The root cause I see is too many variables and users not understanding what all those variables mean. Variables? Cobra wise a top few:
- front and rear Cobra 'pin drive' wheels required different center section thicknesses because front and rear hubs were significantly different lengths. Front wheels installed on rears leaves few threads exposed. Rear wheels on front are too narrow in cross section for the center lock nut to clamp.
Click the image to enlarge.
- because of the item above a racing Cobra that was factory prepared had four different center lock nuts. There was left and right of course but there was also front and rear. Yes, four different center lock nut parts per car. (This problem was not addressed with a design set change until mid 427 Cobra production.)
-Halibrand made wheels for other types of cars had their own set of design dimensions that usually would not just ‘bolt on’ to a Cobra.
- Halibrand produced many variations in center lock nut critical dimensions depending on the wheel and car they were intended for. The critical ones, means required to fit and work properly, length and diameter male center lock nut cone, working diameter of threads, and thread angles (like 55° or 60°).
-Reproduction wheels and nuts made by many people in multiple countries since the mid 1970s are not always dimensionally (critical) the same as genuine factory parts.
-Reproduction hubs made by multiple people over decades of time since the mid 1970s are not always dimensionally (critical) the same as genuine factory parts.
There are others but for brevity I’ll stop there. If a user combines parts (hubs, wheels, and nuts) that are not dimensionally compatible no amount of safety wiring is going to do any good except provide a type of warning. The tapers of wheel center and nut center must engage sufficiently that no other interference is encountered. Example: A certain Cobra participating in a tour Martha and I participated in came with seconds of losing its right front wheel more than once in a single day of touring. Safety wire stretched and broke, multiple wraps of safety wire broke, and finally on the last leg of a day’s driving back to the lodging for the night multiple wraps of safety wire, two very large plastic wire tires, and two large band type hose clamp all used together would not stop the center lock nut from backing off. I tried to tell the man that he the center section of the reproduction Cobra style (looks like something Halibrand made) wheel was too thin and that when they beat the wing nut on they just ran out of threads of the hub. To illustrate, the offending front wheel was still loose enough to shake and rattle against the hub with the nut beat ‘tight’ to their exhaustion. Subsequently a restoration shop solved the problem with parts that would tighten in the taper zones.
We have a modified (was vintage raced about a decade) Cobra that came to us with the magnesium Halibrand made wheels from one of the cut back door Shelby prepared race Cobras. I am not keen on playing / hard driving on old magnesium wheels so I had a custom set of aluminum wheels made to Shelby dimensional specifications where front wheels and rear wheels have different and correct thickness center sections. I also used 1960s Shelby nuts correct for not only left and right but front and rear. I do not safety wire the nuts. I do use black ink to match mark nuts and wheels. If the marks get out of alignment, rare, it is because the nuts get tighter if they do move, usually don’t. Getting the nuts back off after hundreds of miles driving can be difficult, I finally upgraded from a 2 lb lead hammer to a 6 lb lead hammer and it can still be tough to get the nuts loose.
Conclusion: To me if a Cobra (427 Cobra, GT40) has trouble keeping center lock nuts tight it is a sign of at least one dimensional issue in the mating parts.
Dan