Cosworth Transmission upgrades

2WD

The 2wd Cosworth's all come fitted with a Borg Warner T5 gearbox as standard which is essentially a very strong unit. In addition 2wd cars are fitted with a 7.5 inch rear diff with a viscous coupled LSD. Again it is a reasonably robust item making the 2wd transmission fairly durable from the factory! However both become weak links and I shall prioritise the order in which you should upgrade below. As an initial starting point the standard rear diff will cope with around 350 - 400bhp depending whether the car is used for standing launches such as Santa Pod, where as the T5 gearbox will cope with 400bhp again dependant upon abuse.

Upgrading the 2wd transmission:

1.  The standard 7.5inch Ford diff is a very strong unit but the weak links are the original planet gears. Thus the first point of upgrading should be to change the LSD unit to either a Quaife ATB or a ZF/Gripper plated LSD. All of these units replace the standard planet gears and hence remove this weak link. The crown wheel and pinion can be shot peened at this time and built correctly with the back lash optimised for strength this diff will then be reliable up to 500bhp!

2.  The gearbox is normally the next to give up the ghost, being unreliable in engines over 400bhp. It is usual to strip teeth from either 3rd or 5th gear or break selector forks if changing very aggressively. Notchy or crunching boxes are not uncommon but this is down to worn synchro's rather than broken parts. Several upgrade options exist but I shall mention only two here. The first is to change the box to a Tremek TKO, but I no longer advise this route. I now favour the big tooth Quaife gear kits for the T5 with stronger selector forks supplied by CTS.

3. Finally with the above two upgrades the final weak link returns to the diff, this now being the 7.5inch crown wheel and pinion. At power levels over 500bhp it is not uncommon to strip the teeth from the crownwheel! The only two options I advise are either a Ford '909' 9 inch rear diff (using a 3.6:1 ratio if available) or alternatively the latest option is a HUGE 10.5inch diff modified to fit exclusively by ZOO Motorsport. This diff is available with uprated driveshafts and CV joints and along with an uprated prop completes the transmission upgrades.