The mechanical centre PTO is fitted to the back of the transfer box and drive is transmitted via a dog clutch that engages onto the main gearbox output gear. Drive is selected by moving a lever that pushes a simple fork running in a groove machined around the circumference of the drive dog. The centre PTO has two main purposes. The first is to power items such as welders and compressors mounted within the vehicle via a V-belt pulley or short propshaft attached to the output flange. The second is to power the rear PTO mounted on the rear crossmember.
In total there were seven different variations of mechanical centre PTO for the Series Land Rover including the types fitted to the ‘One-Ton’ / IIb Forward Control and the Series III Stage I V8. Some changes and types are more obvious than others.
Approximately 2000 of the first variation of centre PTO were manufactured, these being fitted to very early Series One 80in and pre-production models. The serial numbers of this type of PTO lie between 860001 and 862000 but it appears some are stamped with just a letter ‘T’. An early centre PTO can be identified by the presence of a large circlip retaining the main bearing within the aluminum housing. An additional circlip on the output shaft retains the smaller bearing to the shaft. The oil seal housing is made of steel and has no mudguard to protect the oil seal. The selector for this type of PTO was also limited to 2000 units. These early selectors can be identified by the presence of counter-sunk screws retaining the inspection plate, later examples having setscrews instead. Very early selector units are not stamped with a serial number, but have the experimental ‘X’ mark cast into the selector housing replacing the number ‘two’ of the anticipated production part number.
It is worth mentioning that the numbering system used for the PTO’s was separate to the vehicle system and cannot be used to date a PTO in the same way as a vehicle. This is also true for the rear PTO and pulley. The numbering sequence began at 860001 and once this range had been used up it continued on to 87000 and so on. By the early 60’s, centre PTO’s began with ‘88’. Selectors had their own serial numbers and because there were more selectors than centre PTO’s you can often find selectors from the late 1960’s with a serial number beginning with ‘10’. (90 prefix seemingly not used) By the early 70’s this numbering system was scrapped and a new system was introduced. A small stamping on the selector housing was used initially normally beginning with the letters ‘A’ ‘AC’ or ‘ALV’, followed in the mid 70’s by the a green Aeroparts makers plate. It is very rare to find a PTO and selector with matching or concurrent numbers and can often be a few hundred out of sequence.
The second variation of centre PTO can be identified by the deletion of the two circlips and the associated grooves in the aluminium housing and shaft. To remove any end-float incurred, shims are placed between the oil seal housing and aluminium bearing housing. It became apparent that the PTO output oil seal was easily damaged, as it was unprotected. To combat this a mud-flinger and shield was added to the oil seal retainer and output flange. Initially the steel oil seal retainer was machined to fit the mud-flinger and this can be described as the third variation. This third type is probably the least common as it wasn’t long before the oil seal retainer was modified further.
The fourth and most common variation was introduced around the beginning of the Series II and remained in production until the end of the Series III. This variation now had an aluminium oil seal retainer complete with mud-flinger and shield, replacing the earlier steel type. Most of these PTOs are in the ‘87’ and ‘88’ serial number range with later PTOs having no serial numbers at all.
In October 1960, the awkward under-seat PTO selector that was accessed by lifting the centre seat and an access flap was discontinued and redesigned. The new design now protruded conveniently from the heel board near the handbrake lever. The selector mechanism was revised another couple of times in the late 60’s and early 70’s with two new selector castings. The new castings were of a universal design allowing them to be machined for both standard gearboxes and the ‘One-Ton’ type. With the introduction of the six-cylinder normal control in 1967, a lengthened selector rod was introduced to cater for the position of the six-cylinder gearbox, seated a few inches further back in the chassis. Later selector rods were designed with two holes to cater for both four and six cylinder models.
A very rare centre PTO for the standard Series Land Rover gearbox was the Heavy Duty version and this was fitted predominately to vehicles with inboard welders or compressors powered by the three-groove V-belt pulley. The PTO itself was longer than the usual centre PTO, allowing the pulley to be reversed thus distributing the load over the rear bearing. The selector lever was of the underseat type but had a longer cranked lever to give extra clearance between the operators’ hand and the drive belts. It appears this type of PTO was available throughout the 1950’s but was discontinued by the early 1960’s.
The differences between the normal gearbox and the all-helical ‘One-ton’ and IIB Forward Control gearbox necessitated another type of centre PTO. The general appearance of the PTO is similar but the overall length is shorter than the standard type. The input splines are much shorter and the rear mainshaft support bearing has a larger internal diameter to accommodate the larger gearbox mainshaft tip. The main bearings also differ to the standard gearbox type. The selector dog is machined shorter than the standard type and the selector fork is cranked to allow it to fit over the drive dog that sits further back due to the longer gearbox mainshaft. A small quirk with the Series IIA and Series IIB Forward Control PTO selector knob was that it was blue and not the usual black.
With the introduction of the four-speed LT95 gearbox in the Range Rover, 101 and Series III Stage I V8 another new PTO was designed to suit the gearbox. The unit was self-contained, deleting the need for a separate dog clutch and selector mechanism. Instead of conventional ball bearings, tapered bearings were used instead. This centre PTO was short lived due to the replacement of the LT95 gearbox with the new five-speed LT77 gearbox and LT230 transfer box. Many of the LT95 type PTOs remained unsold and were dismantled for scrap by the manufacturer.