Changing Our Mini's Rings and Pinion Gears

December 26, 2012

1967 Cooper

Changing the ring and pinion gears

helped our final drive ratio

1967 Cooper

The pinion gear for the 3.0:1 final drive

was physically too large to fit in the retainer

1967 Cooper

The retainer was ground down so the pinion

gear would not interfere

While rebuilding our transmission we got into a discussion with the folks at Mini Mania about final driver ratio selection. The standard ratio for the 1275cc Cooper S was 3.44:1. And while our car still had this stock, standard ratio, Mini Mania owner, Don Racine, suggested that if our intended use for the finished car would be some highway use and higher speed, long distance rally work, then we may be happier with a higher (lower numerically) final drive. He pointed out that with the stock 3.44:1 final drive ratio, a Mini Cooper is straining and turning very high rpm at today’s legal highway speeds.

As we had tweaked our head a bit and had a little hotter cam, our engine would be good for another 5-10 percent more horsepower. So we felt we would still be able to come off the line even with the higher final ratio.

Generally, we like to test everything for ourselves, but we had no desire to take apart the gearbox twice, and Racine and his crew have many years of Mini experience, so we trusted them. He recommended a 3.10:1 final drive as a good compromise for overall drivability.

There are a few tricks needed to install the physically larger ring gear, which we will get into when we start our story series in the May issue of Classic Motorsports.