Looking for 915 transmission info.

[Chris Pomares]

I have a LWB project coming up and it looks like I'll be in the hunt for a 915 transmission. I know what I'm looking for in a 901 but weak in 915 knowledge. What are some good sources to read up on the 915. The engine will be a Supertec 2.8. Mag? Aluminum? Years. etc.
Thanks, Chris

[Jon B]

Chris,

If you're buying a complete transmission core, then look for a 73.5 to 75 transmission, which have mechanical speedometer drives and CV flanges to match your LWB axles.
The 70s magnesium housings had fewer problems than the later aluminum housings. The mechanicals can be upgraded as far as your budget allows.

Several forum regulars here have extensive knowledge of 915 transmissions.

Jon B.
Vista, CA

[37yrold911]

Mg case strengthened will be strongest

The '73 is harder to repair in places than later years

a '75 will have gearing that is not far off from that of an SC-RS

I need to jog my memory on this stuff... maybe it will come back to me in a bit ;]

[Jon B]

The '73 is harder to repair in places than later years

The main downside to a 72 or early 73 is the input seal, which is only accessible from inside the transmission.
This changed in mid-73, with the following serial numbers:

915/02 from serial number 7337375
915/12 from serial number 7230507
915/08 from serial number 7830838
Special transmissions from 7931031

The 76 model was the first with a removable clutch bearing guide tube. Earlier transmissions can be updated for this by machining the main housing.

Jon B.

[Mr9146]

I have an electric speedo, euro 915 with oil cooler and LSD if you're interested. Less than 5000mi on it since it was rebuilt. It's currently in my car so I know it works right.

$6000obo

[37yrold911]

1st - you might get by with a typ 911 - wider gears than a 901 IIRC; you'd get the wonderful light shift feel, and the outstanding road-racing pattern but would have to be careful and might need to do some mods to it (e.g. a 904 mainshaft); it is lighter too

any 915 will just not feel as good IMO

a '75 is the 1st year with an 8:31 R&P which is likely what you want; early '76 still has mech. drive; elec. drive starts in mid or late '76

stronger mainshafts start in '76 as does the externally replaceable guide tube ('74 has a removable guide tube)

stronger side cover starts in '78 but Wevo or SRP fabbed these up

Mg cases do better in terms of anchoring the pinion roller bearing than the Al cases (no insert)

you can easily build a nice franken-tranny if you can get parts...

[Jon B]

... early '76 still has mech. drive; elec. drive starts in mid or late '76

Most of these things are well documented in various factory manuals and bulletins.

Service-Information 911S Model 76
1st edition, Sept. 1975
All vehicles are fitted with an electronically controlled speedometer.

And no, a '74 does not have a removable guide tube.



Jon B.
Vista, CA

[37yrold911]

you are saying it is not removable? or not externally removable?

[sithot]

Nice link for information. Also good source for gears, etc.
http://www.gboxweb.com/915specs.html

[Jon B]

you are saying it is not removable? or not externally removable?

Prior to the 76 model, the guide tube was set in the housing with an epoxy-like adhesive and not meant to be removed.

The photo below is a 74 guide tube, similar to all guide tubes from 73.5 to 75 model years. I can post another photo of the serial number if necessary.
The manual page below is from the same Model 76 Service-Information booklet, introducing the new, removable bearing guide tube ("guide sleeve").





Jon B.
Vista, CA