Jaguar Specialties
Innovative and Unique Products for Jaguar Cars

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Last Update 8-20-23

Jaguar XJ40 Vacuum Brake Booster Servo

Upgrade Conversion

1987-89 XJ6, Sovereign and Vanden Plas

This great conversion kit enables the 87-89 Jaguar owner to replace the troublesome, expensive, and quirky Jaguar hydraulic brake servo booster system with a reliable, trouble-free, and maintenance free vacuum powered system. No more endless green fluid leaks, weird (and inconsistent) boost to the brakes, expensive repairs, or erratic error messages to the dash. Some other key details of this conversion are:

  • Everything required for the total conversion is included- nothing else to buy

  • Fits all 87-89 XJ40 3.6L models: LHD or RHD with automatic transmission (contact us for info on manual transmission installations)

  • Retains the original Jaguar brake master cylinder (and it is not even required to disconnect it from the car for kit installation!!)

  • Retains the original Jaguar ABS system (with full function)

  • Includes detailed, illustrated installation instructions  (installation time is about 3 hours with basic tools )

  • Over 450  kits have been installed worldwide as of December, 2020 - United States, UK, Canada, Australia, New Zealand, South Africa, Germany, France, Spain, Holland, Finland, Denmark, Egypt, and elsewhere- XJ40 owners just love it!!!

  • Kits are available for immediate shipment- please Email us for current kit pricing and shipping cost to your area.

For more detailed information on the conversion, please read on

Jaguar used a very unusual engine driven hydraulic system on these cars to power the brake servo/booster and to also power the rear self-leveling system. To be kind, the system was very innovative (and complex), but was also a source of enormous trouble, customer dissatisfaction, and heavy warranty costs for Jaguar in that period. While the factory did offer a conversion kit for the rear suspension (to use standard, non-self leveling shocks and springs), they never offered any real fix for the quirky, troublesome hydraulic brake servo/booster system. This has remained a problem on these early models until today, with frequent hydraulic leaks, expensive repairs and replacement components, and a continuing source of frustration.

However, Jaguar Specialties now offers a practical, economical, and easy to install vacuum brake servo/booster upgrade for these models that is a perfect fix for these cars, and works beautifully (and is US Patent Pending....). This upgrade does away with the complete power hydraulic system, thus eliminating all of those troublesome and expensive components. The stock master cylinder and ABS system are retained and are fully functional. Due to the added available boost in the vacuum upgrade, braking performance is noticeably improved, with virtually no long term maintenance requirements. It is truly a great solution to the lingering, expensive, and continuous problems these cars have with the original power hydraulic system.

The photos below show the booster conversion installed on stock 6 cylinder XJ40 cars, both LHD and RHD (automatic trans installations are shown, but the kit can also be adapted to manual transmission  XJ40 cars- please inqure). The key to the conversion is the booster/servo itself- chosen to fit the available space, perfectly match the the braking system's requirements, and be very reliable. A rebuilt booster and all other required hardware are included in the kit- there is nothing else to buy.

This upgrade can easily be installed at home by a do-it-yourselfer with basic automotive skills, or by your favorite repair shop. Detailed, illustrated instructions are included with the kit, outlining the step-by-step process to complete the conversion.

As of December, 2020, this upgrade has been installed and is running on over 450 XJ40 sedans worldwide (both LHD and RHD, 6 cylinder and V8). Customer feedback has been extremely positive, including many repeat orders from professional shops installing the conversion on customer cars. Here is a sample of customer feedback from installations both in the US and overseas:

".....The car has been used almost daily since the install, with no problems whatsoever. The positive feel of the brake is still a real treat, compared to what it was before. The car just passed an MOT (Ministry of Transport) roadworthiness test - the examiner didn't even note or mention the brake upgrade - it looks so standard!....."


".... I have had the braking system up and running for a while now and am extremely pleased with performance. Pedal pressure required for normal adequate braking is fairly similar to the original booster unit, however pedal feel is more fluid and no pulsing is felt through the pedal. Much improved pedal pressure/feel when braking at low speeds. ABS performance has also improved (I did a few emergency stops to test the system thoroughly), as the car pulls up more confidently when required. "


"..........the more I drive it the better I like it.........................."

For more info on this upgrade, please feel free to Email me, or call. Kits are in stock, ready to ship to anywhere in the world. Note- as this conversion removes the power hydraulic system from the car, any vehicle still equipped with the original sytle self-leveling system will need to be converted to standard rear shocks and springs. By now, most XJ40 cars have already had this upgrade done, but if you should still need to do it, Jaguar Specialties also offers a very reasonably priced and complete kit to do so. Please inquire.

LHD 6 Cylinder Installation

RHD 6 Cylinder Installation (courtesy of an Australian customer)