What's the difference between older and newer 915 transmission

[brooklynporsche]

What's the difference between older and newer 915 transmission
Is the 915 used on a 1974 2.4 engine different from the a 915 used with a 1978 3.0.

Thanks

[Flyboy333]

In my limited knowledge of these things, I believe some of the sliders and things were beefed up a bit, and the synchro design changed a bit. Tony at TLG showed me this when he rebuilt my '77 (I believe) 915/44. There may have been more changes as well.

[wowzer911]

Don't forget the ring & pinion gear differences 7:31 vs 8:31

[brooklynporsche]

Can I see any visible difference

[Flyboy333]

If you look under the transmission, there should be a flat bar that sticks out of it, and it should have 915/##, this can be used to find the year, but it may have been worn off, in which case I'm not sure how you can tell. Other pelicans will surely know however.

[Fishcop]

There is major seal difference in the earliest boxes - mainshaft seal can only be changed internally (pain in the @ss).

Speedo drive is another issue to consider - mechanical up to about '77, electronic after that. This also seems to coincided with a change from magnesium to aluminum. The later box also uses an Omega spring to assist the clutch lever.

[hdbmw]

All the above is true as well as a significant difference in the diffs. The early 915's diff resembles the "901" and the later 915's diff has a much beefier housing and ring gear flange (as well as larger/deeper side & spider gears). Then there's the coarse vs. fine spline output flanges.

[hdbmw]

Just wanted to add that in the example you gave, the early box will have the coarse output flange for the larger 4-bolt/2-pin cv joint and the SC box will use the fine spline flange for the smaller 6-bolt cv.

[gtihop]

I heard somewhere that the newer 915 in the 80 's careera era also had stronger pinion and input shaft bearings to help eliminate the pinion race problems. Can anyone verify this as i am soon going to be looking for one for my SC?

[wowzer911]

Can I see any visible difference

Earlier cases were magnesium alloy, where later cases were aluminum.
So gray vs silver

[RoninLB]

my 1977 is electronic speedo

[Bill Verburg]

Originally Posted by brooklynporsche

What's the difference between older and newer 915 transmission
Is the 915 used on a 1974 2.4 engine different from the a 915 used with a 1978 3.0.

Thanks

Yes, though there were no 2.4s in '74 only 2.7s
the previous responses pretty much covered it
but functionally if your are considereing a t/p the big difference is mechanical speedo on '74, electric on '78 and the clutch activation fulcrum

gearing is different
case material is different
internals were improved in terms of strength annually