XK150 Girling brake booster (servo) replacement
Worth changing out for a diaphragm type booster?
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It is possible to have the original Girling brake booster (servo) fully rebuilt, but is very expensive, and the end result is still an archaic piston-based design.

My first step was to fit a Chinese replica of the Lockheed LE10117 diaphragm-based booster available from many Jaguar parts suppliers. I ordered this booster in December 2013.

When I replaced the Girling unit, it was not difficult. I had to make some additional supports for the Lockheed unit, but I did not have to modify anything related to the body or the compartment. The end result was an undetectable change because the Lockheed booster fits nicely and is hidden in the Girling unit compartment behind the left front wheel.

However, I did not get any boost performance from the Lockheed unit, despite the advertised gain.

Three years on, in 2017, I decided that based on the experience of owners of three other XK 140/150 cars and the lack of boost improvement from the Lockheed unit, I would replace the Lockheed unit with a PBR VH40R, the standard model that produces 10,100 kPa output from a 3,100 kPa input (3.2 ratio). In PSI: 1470 PSI from 450 PSI. The VH40 has a diaphragm area 20% greater than the Lockheed unit.

I made a cradle for the VH40 to properly support the unit, and to ensure that the brake cylinder was tilted slightly upwards from the diaphragm, to take advantage of the bleed nipple on the 'nose' of the unit (see photo).

The end result after road testing is an improvement in boost, thus a lowering of the foot pressure needed.

Next issue is to consider is whether to fit the Reservac vacuum reservoir fitted to XK150s from November 1958, and to all early E-Types. I have a new reservoir and associated vacuum valve, but the model supplied is a Mk 2 saloon/E-Type part and bigger than the unit fitted to the XK150.  I'll have to figure out how to mount it near the VH40. A future project!

I've kept the Girling original and it's stored away with the other original parts I have removed from the car. In 2017 I dismantled the Girling unit and found its bores to be in perfect condition, having been stainless steel lined in June 1999. With a US$150 seals and gaskets kit, the Girling unit could be quickly returned to service.
 

brake booster

PBR VH40R booster