Horn Push fixation on Steering Wheel for XK 140 and 150
The Steering Column Control (Jaguar C.5531) is a Lucas manufactured assembly of a Top Cover with Lucas code 32902/E.
Part of this assembly is a Plate for fixing of Control (Lucas 330614) made of (zinc?) plated steel sheet of about 1 mm.
The complete assembly is fixed to the Steering wheel via this Plate 330614 by means of 4 Grub Screws C.1037 on the standard wheel and often 3 Grub Screws on wood rim steering wheel hubs. This Grub Screw has a part number that dates from 1938 or earlier.
The Grub screw has a hexagonal socket to be used with an “Allen” key (or “Inbus” in most countries) and a pointed tip. The point should hold the Fixing Plate in position whereby the 45⁰ angle should push the Plate down on an internal rim in the Steering Wheel centre (see photos above).
The original thread of the Grub screw is difficult to determine, but there are only 2 possibilities considering for this Grub Screw:
- 2BA Diameter 4.70 mm Pitch 0.81 mm Often used by Lucas
For reference the data of the following threads:
- UNF 10 – 32 Diameter 4.83 mm Pitch 0.79 mm Later introduction of UNF
- M5 Diameter 5.00 mm Pitch 0.80 mm “Continental” thread, not UK
The grub screw has an overall length of about ½ inch. Roger Payne mentions a length of 7/16″ but this might be experienced as a bit short as the complete grub screw normally enters far into the screw thread. Note that the original screw may well have been replaced meanwhile by another type. Especially “Imperial Grub screws” are not easy to obtain, but they are still out there.
The UNF 10-32 Grub Screw may be an alternative in the USA. The pitch is again 0.79 mm but the diameter is a little bit larger with 4.83 mm.
Fortunately, an M5 version is readily available everywhere and can be used as a replacement after the thread has been re-tapped with M5. This is feasible as the thread pitch is identical within 0.01 of a mm. Therefore, only the diameter of the threaded hole is increased from (worst case) 4.70 mm to 5.00 mm. The metrical version is readily available: search for DIN914 M5 x 12 or M5 x 16 as an alternative. They use a 2.5 mm Allen or Inbus key.
There are basically two types of Grub screws with hexagonal socket: with “Cone” point or ”Cup” point. The above picture makes it clear that this construction absolutely requires a “Cone” pointed version.