Why does only the 923 gearbox fit the 912E

[TooBrash]

I've heard the knowledgeable, (who I should ask in addition to this thread,) say that the ratios in 912E and contemporary 911's are better swapped, which further distresses the availability of 923 spares for 912Es if true. What's the snag in putting a 915 transmission onto the type IV motor if a clutch disk fitting the shaft is substituted? I understand I wouldn't bother with fitting hydraulics if aspiring to a G50, if those use such linkage, but would think retrofitting more ubiquitous transmissions worthwhile. Light research implies the mounting fasteners are the same position and radius.
If that ain't so, what about flipping the ring on 914 tranny; is the mismatch of mounts too drastic for that to happen? I assume a 091 or bus 4-speed would required completely messing the body up, but it would be nice to have a beater for the duration of having original unit abroad being rebuilt.

[Jaems]

The 914 uses a 901/902 transaxle. These were for the short wheel base cars. The 912E is a long wheel base car. If the 915 bolts up then it should work. However, the gearing may be too high for the 912E type engine, which would mean lost of performance.

Your would be better to go to the 912BBS and to the 912E section for types of transaxles that can be used.

[bh912e]

The 923 is a 915 trans with 901 clutch splines on the mainshaft. The gearing is also more suited for the 4 cylinder engine. You can bolt up a 6cyl. to the 923, and a 915 to a type 4 engine.

[Matt Monson]

Why would one flip the ring and pinion in a 914 box, when a 65-69 901/911 gearbox is the same thing with the ring and pinion already in the right place and the right style clutch?

The 923 gearbox is a 915 with a 901 splined mainshaft. You can temporarily put in an early 911 gearbox while you go through yours.

I would also disagree with the remarks that the 923 is geared for a 4 cylinder engine. It uses the shorter 7:31 ring and pinion, just like they used in the 72 and 73 911 models because the type IV engine in the 912E is lower powered, so the mechanical advantage of the short ring and pinion helps it get up and go. However, the 7:31 ring and pinion and 923 gearboxes in general have historically been desireable to people with 911sc and 3.2L Carrera racecars looking to go faster. The 923 gearing is good against a type IV. It's great against a 2.7l RS replica engine or a hot rod tuned 3.0l.

[TooBrash]

These replies have been informative, and I will be repeating parts of them to myself in the weeks ahead. I surmise location of the transmission mounts would be an area of difference between SWB and long, and my eye was on 914 units because of cheapness. I am happily not pressured by any aspect of the reliability of the 912E, the shifting being adequate, and only one episode of pushing, rectified by a check of the computer plug. Its predecessors included a bus and a MB diesel the service bible which I took to a hearing to prove absence of capability to speed, successfully. I have heard many advantages of the 6's especially in Octane magazine, but I'd think my neglected marque would have it all over these when it comes to getting away with lugging. And midi-controlled recordings of RS exhaust could be mixed into the music system.
Thank you repliers

[Matt Monson]

Very often when people sell an old 901 gearbox they include the mount. I'm pretty sure the mount on the chassis hasn't changed over the years. It's just the piece of metal that holds the gearbox up. I've probably got one out in the shed if you need one...

[Jaems]

One of the problems will be that the CV"s will not match up from the SWB to the LWB.