A+ Gears in the Older 4-syncho Mini Cooper Gearbox

Here I show the modification to the 22G1128 gearbox case that allows running a full late A+ Gearset from a Rod-change transmission. The modification allows the case to accept the 3-step layshaft that is needed for the A+ style laygear. This is a viable option as most of the small input bearing mainshafts have passed into oblivion, and finding a good set of gears, particularly second gear in the pre A+ helical pattern is getting difficult… and expensive.

Running A+ (or even the large bearing “intermediate gears prior to the A+, including the close-ratio 1275GT type if you can find these) provides a number of upgrades to address weaknesses. Besides the stronger 3-step layshaft and gear, you get the larger input bearing mainshaft, and the corresponding stronger input gear. The later gears also have a different coating on the synchro cones of the gears which lets the baulk-rings (synchros) work better, and is more durable (it has a black, almost “soft” when oily texture compared to the shiny metal of early gears).

This is a great upgrade, as the early small bearing type were used on tiny engines, and take a real beating when asked to perform with big-bore engines making 4 or 5 times the power and torque.

Next, I’ll be installing the differential, then we’ll confirm our Idler-gear end-float.

4 replies
    • Jemal at Cooper Road Mini
      Jemal at Cooper Road Mini says:

      Next is the differential set-up, then we’ll button up the gearbox and set it up to the flywheel housing to verify our idler gear end-float.
      I hope these posts are sort of a random-access workshop! I keep them short and specific to the steps described. Usually, when we take on projects like these, we get stuck at certain steps or problem areas. I think we have grown a little accustomed to finding quick and convenient solutions. There are some good videos out there. Mini Mania had done some very thorough gearbox rebuild videos. Often we lack the patience to sit through 45 minutes to find a quick answer we’re looking for.
      You earlier question, I was Mini Mania’s engine shop from 2001 to late 2008. I pushed hard to start doing videos but we didn’t have the skills and equipment of Brendan McRae, purchasing manager, and producer of most of MM’s videos. So I’ve built dozens of engines/ transmissions, and figured out all manner of improvements and work-arounds!


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