Six speed automatic transmission for the V12!

KWE offers the ultimate upgrade for the V12: A six-speed modern automatic transmission conversion! Most 5.3 V12 XJSs had the GM400 3 speed auto transmission fitted as standard. While undoubtedly smooth-shifting and very rugged, this old 70’s ‘box was slow, inefficient and of course was limited to three forward ratios. The later Jaguar 6 litre used the slightly better GM4L80E with electronic shifting, but it was still the GM400 in new clothes.

While the V12 has a very flat torque curve, it is not possible to get sparkling off-the-line acceleration and low cruising revs from 3 or 4 speeds. The standard Jaguar arrangement means the engine is doing a startling 3000rpm at 80mph. This is not fuel-efficient, especially when the V12 is quite capable of driving the car at 80 at about 1500rpm as evidenced by several manual conversions we, and others, have carried out.

With 6 speeds you can have it all – tyre-burning take-off and quiet, frugal high speed running.
The ZF6HP26/6R60 is a technical milestone with its compact, lightweight Lepelletier gearset (https://www.transmissiondigest.com/lepelletier-planetary-system/) being much the same size and weight as the old GM400, while wasting a lot less energy. The GM400 is often quoted as absorbing 25bhp!

Various options can be specified – standard, or switchable eco/sport mode, steering wheel shift buttons, custom shift maps etc.

Priced at around £13,000 + vat, the conversion takes a few weeks. Please get in touch and reserve your place in the queue. A small deposit will be required for this.