TVR T5 Gearbox
Borg Warner T5 Gearbox
The TVR used a Borg Warner T5 gearbox. Rare in the UK but very common in the US. Its input shaft is a standard 1" (23? spline) the same size as the Rover SD1 and MGBGT V8. It has a reputation for being strong and because of its compact size will fit into an MGB with only a little modification to raise the height of the transmission tunnel below the radio centre console (I used an angle grinder to cut the seams in this area and then "reshaped" the transmission tunnel with a big hammer).
The problem with the TVR T5 gearbox is that places the gearstick about 6" too far toward the front of the car. Fortunately I struck lucky with a call to Bernie Braden at Competition Transmission Services. He turned out to be an expert in T5 gearboxes and was able to modify the gearbox with a Sierra Cosworth T5 tailhousing and associated parts to position the gearstick in almost exactly the right place for an MGB.
Clutch and Bellhousing
TVR clutches are ridiculously expensive. I replaced mine with a normal Rover SD1 clutch assembly for less than half the price and could not see any difference except for the release bearing. I think the part numbers were actually the same.
The TVR bellhousing needed modification to fit into an MGB. For the TVR it had a box casting protruding from the top that held the end of a rose-jointed rod and lever assembly used by TVR to reposition the gearstick further forward. This has to be cut away and a flat panel welded onto the bellhousing to cover up the hole.
The MGB clutch master cylinder seems to work perfectly with the TVR clutch slave cylinder. So this has simply been serviced with new seals and a suitable braided flexible hose. The clutch pipe and flexible hose have been sleeved in heat resistant material as a precaution against exhaust manifold heat, as have the front brake pipes in the area of the exhaust manifolds
The next puzzle was how to mount the rear of the gearbox onto the MGB crossmember. A browse through the Sierra Cosworth parts catalogue at my local Ford main dealer provided part of the solution in the form of a Cosworth gearbox bracket and rubber mount. These could be easily mounted on a flat plate welded to the top of the MGB gearbox crossmember. It also provided a pleasant reminder of how cheap Ford parts are in comparison to TVR and RV8!
The gearbox crossmember has to be mounted a few inches further back from the normal MGB position. This was achieved by bolting through the front holes of the crossmember into the rear mounting holes in the chassis and then drilling through the rear holes of the cross member into the chassis from below to create new rear mounting holes. A long drill will emerge through the floor marking the position to cut into the floor to insert new fixing nuts into the chassis. I had new captive nuts welded into this position before welding up the floor.
The job was finished off with a split speedo cable running from a Ford type sender in the gearbox to the roadspeed sensor mounted behind the dash and then a short cable from the speed sensor to the MG speedometer. These cables were made by Speedy Cables who also be recalibrated the speedometer and rev counter for me.
The T5 gearbox requires a propshaft with a standard Ford Sierra sliding yoke. For the axle end I used the standard MGB axle flange size. This propshaft is definitely strong enough for a V8 even though it is no wider than the 1800cc MGB. It is nevertheless the same diameter as used for Sierra Cosworth racers. The important point is that the universal joints are considerable larger those of the standard MGB.
One unpleasant surprise is that it is impossible to fit the propshaft by sliding the yoke into the rear of the gearbox without dropping the rear axle to gain clearance. Still that is not something I plan to do on a frequent basis.
Top: standard MGB propshaft. Below: custom made propshaft with Sierra type sliding yoke at front and MGB flange at rear. Note that the new propshaft is no wider but the universal joints are much larger. Furthermore the MGB unit has a narrow (and I presume weaker) sliding section