915 transmission

What are the differences between the early 915's and later ones. And are the differences significant? Thanks in advance!

Seung

I just replaced a broken 1 st gear synchro in a '82 SC. In shopping for parts I learned that the earlier 915s had symetrical "Dog Teeth" on the synchro, and latter ones have asymetrical teeth.

That's all I can tell you about, but there is a guy, Dennis, at Motor Meister who can probably tell you everything about them, he rebuilds them.

There's a good illustration in the Bentley book.



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GT911
GordonTaylor@ev1.net
'81 911 SC very very fun
'84 BMW 318i very very economical

Thanks for the reply. I wonder what difference it makes with the asymmetrical teeth make.

Not sure, but it was a design change that Porsche went to, so I'm sure there was a good reason, and it makes it better.

I believe this can be an upgrade. If someone wanted to replace all of the synchros and aynchro hubs. It would be a costly upgrade.

Till around 77 or 78 they had magnesium castings for the case, after aluminum, till 75 they had mechanical speedos, after electric, till 74 they had 7:31 rp after 8:31, starting in 84 euro versions had coolers, only RS versions used this feature on earlier cars,there were minor gear changes over the years you need to check the literature, as previously mentioned in 77 they changed the synchros form Porsche type to Borg-Warner type used by most of the rest of the world.

Is there an easily retrofitted gear oil cooler for the 915? It seems like all you would need is a cooler, some hose and a pump. Scavenge through the drain hole and return through the fill hole. Has anyone done this?

On a related note, what's the best way to check for overheating in a 915?

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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net

All of the 915's both Al. and Mg. case are set up for the cooler( the knockouts and bosses for the bolts are there). The internal parts are quite rare and expensive though, I have not seen them offered anywhere in quite a few years. Most people just use an electric bilge pump. I don't like that solution because it really doesn't provide a spray onto the gears like the factory setup. The oil is cooled though. Another solution is to get one of the 84-86 euro trans which had a slightly different yet effective cooler standard. There were even a few southern US cars sold with that cooler.
A temperature sensor similar to the engine temp is easily mounted, just drill and tap, or mount in the drain.

Hey Jack,

How about a nice 3-1/8" aircraft dual head temp. gauge with your choice of pipe plug or sparkplug-type washer sensor? You could monitor your front cooler temp with one side and the 915 on the other. Wick's Aircraft has both the gauge and choice of senders at this URL: http://www.wicksaircraft.com/showPage.phtml?pagenum=201

You could easily mount one of the 14 mm 'ring' thermocouples under an oversized 'OD' flat waser on one of the 8 mm studs of the lower half of the differential cover on the 915.
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Warren Hall
1973 911S Targa


[This message has been edited by Early_S_Man (edited 03-22-2001).]

Oops.

[This message has been edited by JackOlsen (edited 03-22-2001).]

Bill, you mean 87 not 77 for the Borg-Warner synchros. No 915 trans ever had Borg-Warner cone-type synchros. That's a G50 attribute. As for the asymmetrical firstgear synchro, it would only work properly for first gear which is only down-shifted into. I suspect if you changed the other gears to this, they would be more difficult to upshift but easier to downshift. Besides, 3rd through 5th have smaller diameter synchros than 1st and 2nd.

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Tyson Schmidt
72 911 Cabriolet