I have rolled the earlier post by Geoff Green, details observed by Ian Howe and some of my own research into a single post. Let me know if anyone has more information or edits are required.
Brake Fluid Filler Caps
Filler Cap and Level Indicator for Brake Fluid Reservoir were made by two manufacturers - Sovy Ltd and Lockheed.
Lockheed
These were large black caps marked 'NIVOCODE', 'Lockheed' and some French descriptive text; the spade terminals were vertical. These were used on the first group of cars approximating the outside bonnet lock production with the highest car found so far 875190. The level sensor consists of a float inside a round aluminium cover and were also used on the Jaguar Mk 1 and 2 saloons. Unlike the Sovy caps the wires should be removed before the cap was unscrewed. Many owners did not bother which is why the wires are twisted on most cars but they should not be.
'Nivo' is French for level, 'code' is French for rule, so 'level rule'; Nivocode is not a registered trade name, merely a product range of fluid level sensors. They also made matching brake bottles in glass, 'Nivoclair' ('clair' = clear), which regrettably Jaguar decided not to use
The August 1961 SPC illustrates the Nivocode sensors - C18197 'Filler Cap and Level Indicator':
E/122/1 Owners Handbook (note wires are not twisted):
Note the corrosion caused by water in the brake fluid:
Plastic float:
9600 HP with Nivocode sensors March 1961:
SOVY (U.K.) Ltd 54 Park Lane. Croydon, Surrey
From sometime in August 1961 a revised Sovy design consisting of a multi piece cap with the top of black plastic having horizontal terminals and an attached aluminium screw cap was introduced for production. The design allowed the cap to be unscrewed from the bottle without the need to disconnect the wires. The Patent for the Sovy 'Liquid Level Indicator' was filed on 24th October 1959, revised on 9th May 1961 by Eric Bernard Aird Marsh and granted on 10th April 1963. SOVY (U.K.) Ltd continued to supply Jaguar through the Series 3 E Type and supplied other automotive manufacturers like Aston Martin, Rover, etc. SNG Barratt purchased SOVY U.K. in 1990 and continues to build the filler cap and level indicator.
The early pre-production cars were fitted with a Sovy black cap sensor which had no identification markings as they were themselves prototypes. They were constructed differently to the later sensors and quite crude:
Jaguar (Belgium) photo of 77 RW during the demonstration runs at Geneva March 1961 using black Sovy unmarked caps:
9600 HP during very early testing with unmarked Sovy sensors:
More than one very early production car (e.g. 875039) have been observed with the Sovy unmarked caps and left the Factory with them fitted. As these early sensors were pre-production they could not have been in-service replacements.
From sometime in August 1961 the Factory stopped using Lockheed NIVOCODE and started fitting Sovy sensors of a modified design. These had black caps with 'Sovy' and 'Made in England' markings as seen on on 860058 built in November 1961:
Another November 1961 car:
This style of sensor continued to be fitted until July 1962 when the square bottles were introduced.
NIVOCODE and Sovy sensor comparison:
The black cap changed to a white cap when the bottles were changed from round to square in July 1962.
The black caps are still produced with the Patent numbers added:
In March 1963 a new style of sensor was introduced in an attempt to avoid water ingress. These had a push fit sealing knob (easily lost!):
The new waterproof caps. Note Patent Pending imprint but the patent number does not exist:
In October 1963 a Service Bulletin was issued with advice on an in-service modification:
In January 1964 protective rubber caps were introduced in a further attempt to waterproof the sensors
Dispersed throughout all series of production red coloured caps have been observed. These are original Sovy and frequently used on Lotus's however as many sensors were replaced in service (the aluminium parts corroded due to water in the brake fluid) it is difficult to know whether they were Factory fitted. All the red caps I have seen have the Patent number so, if Factory fitted, mid 1962 until March 1963 when the waterproofed versions with the push on cap were used. My guess is the red caps were in service replacements rather than Factory fit given their spread over all Series cars.
Factory Fit timeline (for concours):
Prototype and pre-production cars - either Sovy unmarked black cap or Lockheed NIVOCODE
First ~500 cars up to August 1961 - Lockheed NIVOCODE sensors as illustrated in the August 1961 J.30 SPC
August 1961 to July 1962 - black cap Sovy sensors with 'Sovy and 'Made in England' imprint
July 1962 to March 1963 - white cap Sovy sensors with 'Sovy and 'Made in England' and maybe 'Patent applied for' imprint
April 1963 onwards - white cap Sovy sensors with Patent numbers and push fit waterproof caps
January 1964 onwards - protective rubber caps, which could be retrofitted to earlier cars.
Trivia: A report by Norman Dewis on the Geneva show demo cars had this to say:
"Brake fluid leaking from reservoir bottles, suggest close inspection of fluid bottles for leaks".
The Patent: Once a Patent is filed (in the case of Sovy - 9 May 1961) the owner can use the words 'Patent Pending' or 'Patent applied for'; this phrasing is converted to the Patent Number once it is issued (in the case of Sovy - 10 April 1963). So any cap produced with the Patent numbers should have been after April 1963 yet they seem to have been made some 10 months earlier! The waterproof cap of March 1963 have 'Patent Pending' on them but the quoted Patent number does not exist; either it was withdrawn or the application was never filed. They seem to have been playing free and loose with the letter of Patent law.