XK150 five speed gearbox choices
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Make of gearbox

Options based on using a gearbox fitted to mass-produced cars include:

5-speed Getrag unit
5-speed Tremec T5 unit

Also, one USA specialist offers a custom-built 5-speed gearbox housed in a aluminium case machined from an aluminium alloy block. Number supplied to date is unknown. 

It appears that as at 2014-2015, the most common gearbox used for an XK five-speed conversion is one based on the Tremec T5 unit.

Buy a bare gearbox or a kit?

Because virtually any mass-produced gearbox used in an XK conversion has to have a custom input shaft length and spigot diameter, the option of buying an off-the-shelf gearbox is not practicable. That's not to say it cannot be done, but the process of adapting the gearbox might be very costly. 

So which kit?

Firstly, the T5 kit for an XK conversion should be based on the "World Class" T5, an upgraded version of the original T5 gearbox.

In the USA, a suitable T5 conversion kit for an XK can be purchased from the 5-Speeds branch of the Medatronic Corporation in Florida. Paul Cangialosi, who is associated with Medatronic Corp, is a person with wide experience in 5-speed conversions. The kit from this company uses a 16mm (5/8") thick adaptor plate, and appears to require a modified flanged spigot bearing which is 6mm (1/4") longer than the Jaguar standard. Also available from this company is a stronger, machined T5 rear bearing housing which is recommended for any T5 unit used for competition.   Read more here ...

There are at least two T5 kit vendors in UK. These appear to be based on the same modified T5 unit as supplied by Medatronic Corp, but appear to both use a 10.3mm (0.405") aluminium alloy adaptor plate, and so both are compatible with the standard Jaguar XK crankshaft spigot bearing or needle roller bearing.

The Medatronic 5-Speeds kit uses a prop shaft that has a sliding internally-splined output shaft on the gearbox end. In other words, there is no flange on the gearbox end.

The UK kits include a sliding rear output flange with Hardy-Spicer drilling. These kits require a custom-length prop shaft. The original XK prop shaft can be shortened, but the practical route is to use a new, non-telescoping prop shaft of appropriate length. The face-to-face length of the prop shaft in my kit was 708mm (27-7/8"). The fixed length prop shaft is noticeably lighter than the XK original.

Be wary: The length of the prop shaft and the design of the sliding output shaft are inter-dependent. The safest route is to buy the fixed length prop shaft from the same T5 kit vendor.

Please note that the T5 gearbox itself is manufactured with metric threads, not UNC or UNF.

For reference for spares etc: My T5 kit was based on the Tremec T5 gearbox # 1352-000-251 ("251" indicates a T5 for Ford vehicle).

A complete workshop manual for the T5 is available from one of many sources on the web. Here's one source ...

Here's a comparison (in a pdf file) of the dimensions of the Moss gearbox and T5 gearbox input shafts, and the shafts' relationship to the flywheel face, clutch plate and bellhousing.

moss T5 input shaft dims

What was included in my kit from England?

- Compatible input shaft of correct length and spigot diameter for the XK150
- 10.3mm (0.405") thick aluminium adapter plate fixed to T5 front face using four 1/2" UNC x 7/8" black capscrews
- Bright steel centering adapter that ensures the XK bell housing and the T5 are perfectly centred
- 10" clutch plate with a 1-1/16" x 10 spline centre (the original XK clutch plate cannot be used)
- Speedo adapter (not of any use - see later)
- Gear lever adapter (needed modification - see later)
- Various bolts and nuts, many not needed
- Seven 7/16" UNC x 1-1/2" setscrews and washers to hold the bell housing to the adapter plate
- - The eighth bolt (and spring washer) required had to be sourced locally
- Flanged longer length spigot bearing (not of any use - see later)

But ...no instructions, no hints, not even a note to advise which type of oil to be used.

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