Transmission advice?

[PorscheNut924]

I am in the long process of rebuilding my 924S one piece at a time. I'm looking into the transaxle rebuild now, and I have a spare 944S transmission in my garage.

The gear ratios for the 924S and 944S are very close, the 944 just has very slightly taller ratios for 1-4 (the biggest difference being 4th gear, with about a 4 mph difference in top speed at 6400 rpm).

Would this difference in gearing be noticeable when paired with the stock 924S engine? I would like to use the 944S transaxle because then I wouldn't have to immobilize my car while having the rebuild done, and I'm also pondering a 16v engine swap (which may or may not happen).

Since more power is not a sure thing, I want to make sure that my choice of transaxle will be fine with the stock 924S engine. I'm not looking for anything spectacular, just a nice road car.

Bonus question: is the torque tube from an automatic 1983 944 the same as the one in my 924S, and/or would there be benefits to sticking with my original torque tube?

[v2rocket_aka944]

you wouldn't notice much of a difference switching those gearboxes.
the internet has said the 944S transmission is a bit stronger than the 944/924S transmission but no one can really explain why.

i believe the automatic tube will work in a manual car but not the other way around - i think the only difference is an extra hole near the front so you can undo the flex-plate coupler from the driveshaft.

[Techno Duck]

The automatic torque tube also does not have the two threaded holes for the shift lever.

I wouldnt worry about the transmission; they are fairly easy to swap regardless.

[PorscheNut924]

It's not so much the swap, as the expense of rebuilding one. I don't want to rebuild the 944S transmission and then find out it makes the 924S engine bog down.

[kevingross]

The ratios of the gears and ring-and-pinion are such that the redline speed in all gears is very close in terms of road speed. The 944S, S2, and Turbo gearbox is heavier (weighs more) but is stronger than the 924S/944 for a number of reasons:
- larger bearings (pinion and input shafts)
- thicker gears
- pinion gear with wider tooth roots
- better material and design of both the open and limited slip differentials
- probably others I am not thinking of right now...

[PorscheNut924]

So, probably a good idea to use the 944S transaxle? That's what I was hoping to hear.

[PorscheNut924]

Another question...the pinion bearing. I've seen this same 97 mm one, 016311220L, listed as both the front and rear bearing for the pinion shaft on different websites. Does it require two of the same part?

[kevingross]

016-311-220-L is the front pinion bearing for 944S/S2/Turbo cars. The rear pinion bearing is either 016-311-375-F or -J, depending on when the transmission was made. (Porsche recently superseded -H to -J for this part.) You can tell which rear pinion bearing is needed by looking for a large letter painted on the steel center section (gear carrier): will be an F for the -F version of the bearing, an N for the -J version (I think). Same casting but machined differently, except that for the really late versions they used a different casting which is much lighter than the earlier ones... but I digress.

There is nothing wrong with the 944 transmission as long as you maintain it. That means changing the fluid on a regular basis, and rebuilding it when the synchros or bearings reach end of life. No fears on using the 944S transmission other than its added weight, and a caution that, yup, you need to maintain it as well!

Hope this is helpful.

[PorscheNut924]

Very helpful, thanks!