Transmission

It was very Important to me to have a decent gearbox in this car, as its something my former Astra rallycar always lacked, and it really compromised the performance of that car. So For the Corsa Im using a Vauxhall F20 unit with Quaife Internals for a couple of reasons, firstly reliability, The Quaife F20 gearkit should be easily capable of handling the power and torque of the 1600 engine, and secondly because it allows me to use the beefier Astra Gte drive shafts, You may already have read in the suspension section that I have modified the hubs to accept these shafts, again this should aid reliability.

First job was to purchase a donor standard F20 box to use for the casing and various internal parts, Next I purchased a Quaife Syncro gearkit and crown wheel and pinion, I have opted for a 4.85:1 ratio on the crown wheel and pinion as I think this should give excellent acceleration through the gears but still give sufficient top speed. Now its obviously very Important to have good traction as well, so the power is transfered to the wheels via a Harry Hockly plate type limited slip differential unit. If you are thinking of a similar set up then its worth mentioning a couple of minor problems.One, the larger diameter crown wheel catches on the diff casing bottom cover so I had to mill a few millimetres off the inside to provide clearance, I simply sprayed the inside of the cover with black paint, bolted it loosly in place then turned the crown wheel which scratched off the paint at the point of contact,then a bit of work with the miller and a grinder and the problem was solved. Second problem arose when I attempted to fit the LSD unit. There is a small alloy 'lump' and a plastic gear shaft inside the diff casing which normally provides a drive to the speedo cable, but I found that the larger plate diff was fouling so it was a case of getting a hacksaw blade and chopping out the alloy lump, with that gone and the plastic gear removed, the diff unit went straight in, held in place with a pair of side bearings.

I also spent some time cleaning up and painting the gear casing to match the engine block and keep things clean. You can see a before and after pic below.

Time to mate the gearbox to the engine and surprise surprise, another snag, the splines on the gearbox input shaft wont fit the splines on the clutch plate, you can read more about that in the engine section, but if you are doing this conversion remember there are a few subtle differences, the clutch release bearing and its guide are different, the bearing fork and the lever arm are also thicker and stronger on the F20, oh and you may find that you have to cut a small notch out of the sump end plate to clear the diff bearing plate.