Hey all, would the standard a12 4 speed last behind an a15 thats rebuilt, balanced, with a mild port and polish and a cam ? If i was to put a celica 5 speed behind it would i have to change the ratios ?

Tye

The factory went to the 60 series gearbox when the a14 engine was installed, & later, the A15. This was because they felt that this gearbox would survive well beyond the warranty period, so they obviously didn't think that the smaller 56 series box would provide the desired level of reliability in every case.

In reality, it's not really the engine so much that will break the gearbox, it's the DRIVER. If you give it a hard enough flogging, then you will break the 56 series gearbox with a stock 1200, but if you drive the gearbox with a suitable measure of respect & reverence, even with an A15, it can outlast the car.
So,... what's your driving style.

Im sensible i guess, ill give it abit every now and then tho, if i was to put a 60 series box in would i have to change ratios etc ?

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nope, the ratios that came in all the datsun raod boxes should never have to be changed if its only going to stay on the road. My question is, do u want to keep the 4spd or go a 5spd? because finding a 60series 5spd is frustrating, i gave up on the idea...

but the 4spds should be common enough, if you look for a sunny or whaterver other cars had the 60 in them. (anyone know from the top of their head?)

I reckon it might survive well behind a "cammed" A15 -- those higher RPM engines usually have less torque.

But the stock A15s have too much torque for the 56-series transmission, even if you drive it moderately.

YMMV

I'm running one with myTurbo'd A15.....
still pulling strong and it's been a couple of months and 2 drag meets now......

I guess a sure fire way to keep the box in one piece is to keep the rubber on the rear less than desirable...

Yes, if you have a modified A15, making power at higher RPMs, the 56 gearbox may work out well.

The ones I broke were not at high rpm, or even under full power. It was taking off in first gear. Not involving clutch dumps or anything like that. The stiock Datsun 1200 gearbox has such a low first gear, it multiplies the engine torque more than B210 or B310 transmissions...