Help with 915 part number

[mmasse]

Can anyone help in identifying what model of 915 is this one?

915/6 7186421

Thanks

[mmasse]

Anyone, please?

[wevoid]

Mario,

You are missing one vital digit.
The transmission number is actually 915/6?

It could be

61
63
68

Have another look.

Even without that info, it's a 1977 or later 915 transmission, so it would have an 8:31 CWP and di not have an LSD when shipped from Porsche

Regards

Hayden

[Bill Verburg]

915/61 718#### is a '78SC 5 spd trans

[mmasse]

Thanks for the info.

Bill, I know you are an expert on this. Would this make a good base for a rebuilt to use with a 3.6 conversion?

Is this the one with the stronger case?

Thanks

[Bill Verburg]

I think that Hayden or Geary are the experts

MNSHO?
It's ok, but you might want to beef it up w/ some of Haydens parts, see Muffinmans recent thread.

I am using a 915/67 and can easily induce weaping at the sides when I get it on in first or second. This is w/ a high torque 3.8RS spec motor, I gotta admit that am worried and monitor it carefully. There will be no more track days on that car and I think that the 3.8 into the 993 and 3.6 w/ Rs cams into the Carrera makes more sense.

[mmasse]

Sorry, i missed Hayden reply when i sent my second post. Thanks Hayden.

Here is the deal. I had finish my 3.6 conversion (993 Vario engine) and currently I am running on my standard '76 915. i am thinking to buy a 915 to rebuild while my standar lasts. i do not have a huge budget, i a I can probably get this '78 SC at a decent price. I was wondering if this would make a good base for the rebuild. I am not sure when the aluminium cases started and if there is any other substantial differences about the 915 models.

I read once that the '86 trans is the strongest, but not sure of the source of this.

Thanks again,

Mario

[Bill Verburg]

Hayden reported that the '76 mg. case is actually a good starting point, beef that up and you should be good to go.

I replaced my 915/44 from the '76 w/ a late case for several reasons
* yes, it is supposed to be stronger, how much I don't know
* rebuilt LSD w/ new friction disks
* rebuilt rest of trans, new syncros, bearing etc.
* integral cooler
* taller gearing

[wevoid]

Mario,

I think we are yet to understand the best 915 package for a 3.6 conversion.

I dont think it's right to assume an Aluminum case is better, or event that a later model is better. There are some generalizations that can be safely made, but as the sample pool of 3.6 conversions is steadily increasing, the types of use, degrees of preparation, wear, tear etc, etc leads to better understanding.

Situations like Bill's weeping side cover are relatively new - this might be an isolated case - or it might be the trend for everyone down the road.

A 3.6 conversion car like BB2 - where Jack goes to the track three times a day - it seems, is likely to reveal some issues too - and not just in the transmission.

It's great that the forum provides the environment to share information - especially when / or if / it is safety critical.

I had an opportunity to spend a couple of days with Norbert Singer recently. I asked him directly - "what was the reason to switch from Mag to Alu on the 915 housings"

He said it was part of a pan-Porsche study of all the Mag components. They had determined that many of the Mag parts were operating at temperatures where Aluminum offered significant stiffness advantages. There was sweeping change towards Aluminum in every case. This ranged from race car parts to production car parts. He made it sound like it was part of an ongoing engineering quest for higher stiffness.

I asked him why they eliminated the iron pinion bearing carrier from the Aluminum cases and he seemed unable to recall. I joked how much business that oversight was generating for the 915 specialists nowadays. I always thought it was ironic that the iron insert feature reappeared for the G50/50 trasnsmission - a real brute in terms of torque capacity.

I still believe the Mag cases are pretty ggod. In many cases they have spent little time in front of much power - like only 150 hp in 1976. Corrosion is an issue - but if you have a nice '76 or '77 and build it with upgrades skewed towards how you plan to use the car, then it will offer pretty good service - directly related to much much use and abuse.

Regards

Hayden