70-71 Pull Type Trans to Early Push Type

[sebastianroher]

Good afternoon,

I am in the process of having my 71 911 pull type transmission rebuilt. I was advised that the transmission can be converted to the early 901 style which is push type. Has anyone here done this conversion? If so, which parts would I need to purchase? Thanks for your help!

Merry Christmas,

Sebastian

[john walker's workshop]

Best to use a '69 case. There's not enough material in the area where the '69 style fork pivot ball would need to be mounted. The '69 and earlier pivot ball is closer to the guide tube than the '71/71 ball, and the fork is different. On the outside there's a casting that looks like you could just drill another hole, but inside, there's a depression milled in that spot, and a steel insert. I suppose you could have it welded up. Then there's the side cover difference with the loop that the 70/71 cable slides through and the early cable sheath that fastens to a small hole in the protruding tab.

[john walker's workshop]

Pic inside a '71 diff housing showing the steel insert for the 70/71 pivot ball and the location for the earlier ball.

[stownsen914]

Were you given a reason why the conversion is recommended?

You’d have to convert the case or buy another one and change the throwout arm, and then get the earlier style clutch and flywheel too. Nothing wrong with the earlier setup, but it’s enough to do I’d want to have a good reason.

[gled49]

Scott’s Independent in Anaheim Ca, has done this mod with success.

[sebastianroher]

Originally Posted by stownsen914

Were you given a reason why the conversion is recommended?

You’d have to convert the case or buy another one and change the throwout arm, and then get the earlier style clutch and flywheel too. Nothing wrong with the earlier setup, but it’s enough to do I’d want to have a good reason.

From what I was told it would be easier to adjust and setup the clutch linkage if it were converted to thr earlier style.

[stownsen914]

Are you having an issue adjusting your current clutch setup?

[sebastianroher]

No,
I'm not at the point yet, my car is still having metal work done. I think that the biggest factor attracting me to this modification is that parts costs are cheaper and the earlier style is more reliable than the 70-71 style.

[djpateman]

The late 70 and the 71 trans cases are reinforced to prevent cracking, so are superior to the 901 cases. The 911 clutch is larger than the 901 clutch and has a higher torque capacity. I would rather have the 911 clutch than the 901 and would consider upgrading my 901 to a 911.

[manbridge 74]

The type 911 pivot ball part was superseded with a much improved design to eliminate breaking. It’s also lighter than the 915.

The best I can tell, if you ordered an LSD you got an aluminum case in 70-71. So we will see how mine holds up as I added an LSD to a mag case 1970 trans I have recently installed.

[jluetjen]

My car's got an aluminum 901 that I'm rebuilding now, and I rebuilt a friend's magnesium 911 style gearbox. If you've got a 2.2 or larger engine capacity, the 911 is going to be a better deal since (as mentioned above) the 911 has a larger diameter clutch that can handle more torque than the early style clutch. The big weakness that I could see in the magnesium 911 is the magnesium side-plate and the intermediate plate. Rather than go through the trouble of back-dating to a 901, I think that it's better (and most likely cheaper)improvement is to just replace the intermediate plate and the side cover plate with the aluminum versions.

The adjustment of either one is not a big deal, just follow the instructions in the shop manual.

[wp935]

Almost 20 years ago at a SCCA event at Laguna, the original style nylon pivot piece broke in the my '70 911T racecar. We replaced it with a newer style metal piece. During the winter the conversion was made to the push style and a LS diff was installed. I think Carquip in Colorado did the conversion and set up the LS diff. I was running a 2.5 motor. No problems going forward and many laps on that setup.