901 VS. 915

I am going to either rebuild my 901 tranny or buy a new or rebuilt 915 tranny for my 70' 911 T. Isn't the 915 a better upgrade: less throw, more precise, less slop, heavier duty? This is what I have heard. Is the 915 a direct replacement for 901 or is there modifications involved. Please reply w/ ur comments and/or ideas it would be much appreciated. Thanx Paddy O

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Yes, the 915 is a better upgrade for the 901, but there are issues in putting a 915 in the '70 911.

The biggest issue is the way the clutch works. In the 901, the clutch is a "pull" type clutch. That is, the throwout bearing is secured to the pressure plate and the release lever pulls on the bearing to disengage the pressure plate. In the 915, the clutch is a "push" type clutch. The bearing is riding on a tube and when the clutch is disengaged, the bearing pushes on the pressure plate.

In addition, the clutch cable for the two transmissions is different. For the 901, the inner cable is securly mounted at both ends and the cable sheath works against the through lever to disengage the cluch. For the 915, the cable, not the sheath, does all the work.

And don't forget the shift pattern. The 901 is what is called the rally pattern where reverse and first are on the same throw. The 915 has the more standard shift pattern with reverse out to the right

So, to mount a 915 in a '70 911, you will have to make sure the type 915 cluch cable will fit and, I am not too sure here, the transmission mounting to the torsion bar tube is the same. That is, is the length of the two transmissions the same?

I had a '70 911 and never did try the conversion so I can't say if it can or can not be done.

Hope this helps.

Alvin

Forgot to mention.

The CV joints may be different between the two transmissions as well. If they are, and I think they are, you will have to change drive shafts.

Alvin

If I had a '70 911, I would not even think about replacing the 901 with a 915, unless you have a heavily modified engine that exceeds tha capability of the 901 (like a Turbo, or a modified 3.6!).

I think the main advantage of the 915 is strength. But, if you car is anywhere near stock, the 901 is PLENTY strong enough! The 915 is a lot heavier, and I think is a harder to shift (a little notchier, balkier, and "heavier"). I love the relatively light shifting and feel of the 901! (Having owned both). A 915 on a 2.2 is just neither necessary nor a great idea, I think.

Brian

Actually, the 70 and 71 911 used a "pull" style clutch with the 901. The early 911s made before 70 used a "push" type, as does the 914. The 70-71 clutch looks and operates very much like the 72 and later clutch and I believe the flywheel is the same from 70 to 77 or so. For 70-71, the end of the clutch cable was fixed on the transmission housing and the "sheath" pushes the fork, kind of neat actually.

One thing I noticed on my 70 was when I had to repair some rust on the two rear seats, I used some tin from a later 911. I found the hump between the two rear seats is larger on the later cars. This might mean the 915 will not fit in the available space since it also is larger.

If nothing else is wrong with the existing 901, the syncro rings are not very hard to replace. Don't forget about the 1st gear syncro hub too.

[This message has been edited by Tim Polzin (edited 02-05-2000).]

The hump is large enough for the 915, it only gets in the way if a G50 is used. The half shafts are the same also. It is only the 1965 - 1968 that have the smaller diam flange/bolt pattern with 6 holes. The 1969 and up have the 4 holes and 2 pins on the flange. There are also 902/02 and 902/05 ect that have special gearing and stronger reinforced cases, you may want to consider as a replacement to the 901 if the 901 is bad. I agree with the guy up the list, a 901 is great if the gearing is find for the application. Seen many 915's under utilized and with the wrong gears for the application.

This is kind of a late reply but I just signed up. I have installed a 915 in a '71 E and yes it can be done. As stated in earlier replys, the clutch will have to be changed to a '72 or later style, Clutch cable and attaching hardware to '72 or later. The hump underneath on the left side will have to be hammered out slightly for clearance for the 915 as the rear unibody and suspension was changed in '72. Also, depending on the year of the 915, you may have to change the inner flange of the stub axles and the CV joints. I believe that 1972 and 1973 915's had the same bolt pattern on the CV's as the 70-71 cars (4 bolt arrangement) On the later 915 cars a 6 bolt arrangement was used. So in summary, it can be done but it will be expensive and probably not worth it. In my case, I had a wrecked '72T and had all of the parts already.

JB