The other thing that seems to help is syncros with only 12 teeth. My 56 series 4 speeds syncros had sets of 4 teeth every 120 degrees versus the other boxes that have teeth around all 360 degrees.

Regarding syncros if you bead blast the syncro cones use masking tape to cover the actual gear teeth and then bead blast the cone mating surface on the gears you will find that if there is no visible wear the end result is like fitting new syncros, But of course much cheaper.

Stewart Wilkins of SW motorsports put me onto that little trick and it works fine in Rally Cars where syncros really get a work out

I'm running an A15 at the moment. The 60 series is plenty strong enough for the level of tune.

I would have to ask if they replaced anything other than bearings in the 63 series, my only reason for using it is as mentioned that it has closer ratios.

Up until about 5 years ago I used an A12 coupled to a 56 series box. As that motor was belting out 80 rear wheel horsepower the small box wasn't an issue. While the A12 does have a slightly better selection of parts it's not enough to offset the gain you get with the larger displacement. With that said I have a fresh A12 short block that I'm holding onto as a back up.

One of the Japanese companies (Kamerei , Cusco, can't remember) said they were considering making a close ratio set for 60 series 5 speeds but haven't heard anything back yet.

Very interesting modification. You bought it rebuilt? Did they just do bearings and synchros? I haven't opened this one up because it isn't suitable for my MG project. Surprised at the condition of these 38 year old 60 series transmissions I have. Also would you happen to be using the A12 mated to your 63 box? I have one of those motors also and hesitate to sell it because there are way more performance parts available for that engine. Might use it for another project.

Ironic you mention this; I traded all of my 56 series 4 speed stuff to OGREInc for a freshly rebuilt 63 series 5 speed last month. Beyond it being stronger it's also possible to assemble a mid close ratio box by using the alternate 2nd gear from a Z20 powered 81-82 510. Th3 alternate gear is 1.9 versus the stock 2.017 in the B210, this may not seem like a lot but when you're buzzing the motor to 8200 it means the motor drops 400 fewer rpm. On my motor the 400 rpm keeps the motor above the point where it steeply falls off, it's worth something like 8 horsepower.

After the 63 series is in I'll be selling of the 60 series because the 63 isn't likely to ever break.

You don't use a 63 gearbox for your race car since it is stronger than the 60 series?

TexasMidget it is as you surmised the bearings and syncros are what wear out. This pretty much goes for the 56 series as well. The 3rd gear syncros in the 60 series in my car would work fine for a street car but with the race car it's worn just enough that it's unhappy with my 8200 rpm shift point. It's OK on down shifts but you have to be very deliberate upshifting.

You forget there is 200 million of you and 20 million of us and the lastA series car here was in the 1980s and we didn't get the 63a boxes or that many 5 speeds

You mention worn out....I have 2 60-series boxes opened up and all I see to replace are bearings. Synchro rings are still in good shape but replacing them while I have boxes opened up. The gears are in excellent shape. Curious as to what else would be wore out.

And I keep hearing how expensive A-series boxes are in Australia. Would that be only for the 5-speeds?

A lot of us down under use the Toyota T50 alloy case 5 speed behind the Aseries approx 1000 to 1500 to set up but a very strong box. Dellow transmissions make a bellhousing to adapt them to the Aseries.
Any Aseries box here are to expensive and mostly warn out and not strong enough .