901 trans

[super9064]

what years did the 901 transmission come in aluminum and do the aluminum transmissions need any of the reinforcements that the magnesium transmissions require when adding HP?

[Flieger]

How much horsepower? My magnesium 911 is fine with RS spec 2.7

Is it the 915s that used a steel bearing retainer on the Magnesium version but the Aluminum ones require reinforcements?

[super9064]

Well, I've got a 3.2 in my 71, and my 68 under construction, motor to be determined, I think the 68 trans is aluminum.

[davep]

The magnesium transmission appeared during the 1969 model year. The usual reinforcement for the magnesium transmission was aluminum parts, so nothing is gained there. The intermediate plates are different anyway. Just be sure to upgrade the simplified differential.

[chris_seven]

There are two major causes of transmission failure;

Torque and speed.

Torque tends to make the shafts try to seperate and chews up the cases and bearing. First gear would be at the greatest risk in a 901/911 type box as the shaft isn't well supported in this area.

High speed can cause general tooth pitting and other lube issues.

I would think that the 901 would struggle at much above 200 lbsft (145Nm) and much more that 8500rpm.

[super9064]

So would it be correct to say there is not a advantage to having a early 901 aluminum cased transmission V.s a 69+ later transmission, or does the same reasoning apply that a Aluminum engine case, is stronger, less porous, less prone to warp.