The Gearbox
On the first MGB V8 conversions before Leyland produced theirs the original 4 synchro overdrive gearbox was utilised, The 4 synchro non-overdrive unit can be used but the extra overdrive ratio is very useful with a low revving unit like the Rover. The earlier 3 synchro gearbox is not suitable as the smaller bell housing will not accommodate a large enough clutch.
The overdrive seems to cope with the increased power but if the unit is switched in and out with full throttle in third gear it can put a strain on the unit, British Leyland, in their production V8, removed this overdrive from third gear by modifying the side of the lever selector that switches the overdrive inhibitor switch, The MGB gearbox is retained in its original position and mated to the Rover V8 by means of an adapter plate. The original B flywheel is machined to accept a larger clutch and this is attached to the Rover crankshaft using a crank adapter fitted with the crank bush. The 1800 B starter is retained and mounted on to the adapter plate after the starter mounting has been removed from the Rover block, A cut-out is also required in the bell housing to clear the nose of the starter and the first motion shaft will need to be shortened. This system utilises a MGC clutch cover, MGB GT V8 centre plate and an I800 standard or roller release bearing. The clutch hydraulics remain standard with the exception of an MGB GT V8 slave cylinder. Some dressing of the transmission tunnel at the font may be required to clear the adapter plate. The B.L MGB GT V8 utilised a modified 4 synchro overdrive box that is identical to the 4 synchro 1800 B unit except for the ratios and the bell housing, which mates direct to the Rover block. The case and the internals have proved to be very weak and extremely costly to repair. Moreover the unit is no longer available from B L. and used units are very scarce and expensive.

The pre-SDI 4 speed Rover P6 3500 S manual gearbox has been used but the poor reliability of this unit, coupled with the fitting problems and the lack of a fifth overdrive gear ratio have made the unit a poor choice,

The SDI five speed gearbox is the ideal gearbox for the conversion and this is the unit that has been used in the RV8, The gear ratios are superior to the B box and the fifth gear is an overdrive ratio. This gearbox seems to be the strongest unit for use with the V8. The box is narrower, higher and shorter and modifications are required to the gearbox cross member, prop shaft, clutch hydraulics, speedo cable and transmission tunnel. The standard MGB prop shaft is not suitable as it is far too short also the Rover one is unsuitable. Early boxes have a manual speedo cable drive and once the speedo cable has been changed this can be utilised obviously the speedometer will need re calibrating, The latter boxes are fitted with an electrical transducer this can easily be removed and the earlier type fitted. The tunnel on chrome bumper models will have to be cut and an extension fitted. On black bumper models the tunnel can be dressed up to accommodate the 5 speed unit although many people have found it easier to cut the tunnel and make good in a similar manner to the chrome bumper mod. Some minor dressing of the tunnel will be required to clear the edges of the larger bell housing. The gearstick fortunately is in approximately the right position and slight modification of the cut-out in the tunnel, towards the offside, will allow the gears to be selected. The remote on the top of the gearbox is a separate unit and this can be repositioned with shim washers if required. Be careful when purchasing a second hand 5 speed gearbox separate from the engine, because this unit was used in a variety of different BL vehicles and apart from the different bell housings the clutch release arm pivot, release bearing carriers and gearstick remotes were different.

With such a powerful engine the Rover automatic gearbox is another suitable alternative but this requires similar modifications to the five speed unit. The size of the torque converter housing requires extensive modifications to the bottom of the heater unit. The gear selector mechanism has to be mounted and obviously the auto has the added problems of an oil cooler and kick down cable. Because of the limited demand for this application we are unable to offer components for this gearbox.



V8 Conversion Project

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