G50 or 915 tranny

[Amstaff]

I recent got a 1988 911 for parts. Not much there but it does have a 3.2 engine and transmission. Would the tranny be a G50 or 915? If it is a G50 it would not fit in my 1970 911 without major modification would it?

[Tippy]

87-89 used the G50

[Amstaff]

Originally Posted by Tippy

87-89 used the G50

So, no go to transplant in my 1970?

[Matt Monson]

Originally Posted by Amstaff

So, no go to transplant in my 1970?

Not without major cutting of your chassis.

[G450X]

If you could find out if it is in good condition (and G50’s seem to be a bit more robust vs the 915), it should bring enough to buy a good core 915 and rebuild it the way you want.

A good 3.2 brings nice money as well - with all the other parts on the car you could make some headway on the 1970 build.

Good Luck

[cnielsen]

You don't have to cut the chassis. Not an easy install but it can be done without modifying your chassis.

[Matt Monson]

Originally Posted by cnielsen

You don't have to cut the chassis. Not an easy install but it can be done without modifying your chassis.

How do you install a G50 without modifying the torsion tubes?

[Craig_D]

Originally Posted by cnielsen

You don't have to cut the chassis. Not an easy install but it can be done without modifying your chassis.

How would this be possible? You can't even use the old sway bar, which is below the torsion tube, so how can you add a G50 without modifying what's above the sway bar?

[sc_rufctr]

Originally Posted by Matt Monson

How do you install a G50 without modifying the torsion tubes?

You shorten the bell housing of the G50. Even then it's not guaranteed to fit. You may need to massage the torsion tubes with a hammer.

[john walker's workshop]

The main shaft needs to be shortened too. That requires a tear down and the shaft sent out for grinding.

[Tippy]

Wouldn't it be a good excuse to cut out the torsion tube and go coilover?

Hate to say it, but I rather hack up the tub than the trans. You virtually cannot add back what is cut off the bellhousing - at least without a major amount of fixturing and time.

[Antomero]

915 tranny’s are underestimated. If set up right, they rock!

[Sboxin]

Tom - OP,

There are plenty of options for your ideas and resources - - But, it comes down to
what do you intend for the use of the car . . . street, track, Restomod, etc., etc.

If it were me - for track use - - 3.2 w/ G50 - coil over conversion - cut out torsion tube.
However, this leads to the "slippery slope" of mods and $$. We have a $$$ wide body,
78 911 3.8L track/race car with an upgraded 915 by CMS and coil overs.

But, instead I would do a good restoration of the 70 911 for a nice street car/Saturday coffee car . . .

Bottom line - you have options . . .

Regards,

[Matt Monson]

For the cost of installing a g50 you can build a wicked 915 race box.

[KTL]

CMS does it https://californiamotorsports.net/collections/porsche-g50-transmission/products/shorten-bell-housing

So does Patrick Transmission > Porsche G50 SBH (Short Bell Housing) By Patrick Motorsports Porsche & Mid Engine Performance Specialists

But it's not something that absolutely has to be sent out to these guys. A local friend cstreit here on the forum had his done locally here in IL after he did some measuring and confirmed those measurements with some research here on Pelican I believe. They simply milled the bellhousing down by a specified amount and cut the mainshaft shorter by that amount, then machined the end for the flywheel pilot bearing and dressed up the splines.

But there's a lot more to it besides just shortening the transmission. You can see a list of the various parts you need to source or recreate by looking at the list of items in the Patrick link. Their list is not a complete list of everything you need. There's a lot more little (and big) details.

You need to use a different clutch. The original 240mm 87-89 clutch housing is too tall. So you switch to the lower profile 240mm 75-77 930 clutch and I believe the conversion flywheel is a 78-88 930 flywheel. But don't quote me on the flywheel.

You need the clutch actuation/hydraulic system. So the simplest way to go is find a donor 87-89 Carrera (or '89 930) pedal set to establish your clutch master cylinder. The kicker here is your '70 car has the brake master cylinder in the pedals. So when you switch out the pedals, that opens up another can of worms of needing to reestablish your brake master cylinder and brake line plumbing. A solution is to use the later style vacuum boosted brake mechanical assembly that mounts in the front trunk. And the early cars need the trunk floor reinforced to mount that assembly in a sturdy manner so the floor doesn't flex when you lean on the brakes.

Of course you have to run the clutch plumbing back to the transmission to feed its slave cylinder for operating the clutch. Also need to have a clutch/brake fluid supply to the clutch master cylinder in the pedal set. You can use one of the '87-up 911 brake master cylinder reservoirs that mounts to the vacuum booster, or just add an independent remote reservoir. Who knows, maybe the reservoir from other hydraulic clutch Porsches can work too.

Need to adjust the G50 transmission mount to account for the shortening. Some people just slot the mounting holes in the aluminum crossmember, or the more elegant solution is Patrick's adjustable mount that is designed from a 915 mount and a slotted section is in the middle of it. They used to custom fabricate this mount by cutting an original steel 915 crossmember and grafting-in a boxed steel section with slots in it. Looking at Patrick's site, it appears their current $485 mount is a CNC machined aluminum mount. Nice (and pricey)!

Need to change the shifter to a factory style 87-89 G50 shifter or use a Rennshift, WEVO or Hargett. Also need to have the original shift tube and coupler to connect with the transmission if you want to use a factory style shifter.

Need to change the CV axles to the later, larger 108mm style that uses M10 CV bolts and a larger center nut with thick washer. Need to change axles because the output flanges on the G50 trans are 108mm with deep recesses.

An '88 G50 from a street car is probably in pretty decent shape but would still benefit from some refreshing. I bet by now the 2nd and 3rd gear synchros are a getting a bit clunky.

[Matt Monson]

Kevin,
You forgot owning the special puller and knowledge required to rebuild the G50. You can’t just machine it with the mainshaft in place. Otherwise your list is pretty complete.

[KTL]

Originally Posted by Matt Monson

Kevin,
You forgot owning the special puller and knowledge required to rebuild the G50. You can’t just machine it with the mainshaft in place. Otherwise your list is pretty complete.

thanks for the reminder Matt. That's no insignificant piece of info. The puller for drawing off the gears is a big sucker with quite a loooooong reach! And yes, the trans needs to be disassembled to do the shortening.

I remember being "wing man" for Chris when he did his G50 install in the '70 racecar. It was some significant work but he got 'er done just like he always does. Thankfully I was able to provide a little bit of guidance/support from what i've gathered over the years.

I still laugh how I remote fed him some measurements of the brake assembly placement from the trunk of my '87 Carrera, by taking some pictures and dimensioning them with Adobe pdf software. Who needs CAD (or whatever it's called nowadays) when you gots digital pictures and Adobe???

[Amstaff]

Thanks for all of the insight. Looks like WAY more than I want to take on. Looks like it will be 3.2 with a 915.

[Geneman]

HEY GUYS clarifying: can you use a stock G50 box, without shortening the bell housing or mainshaft, as long as you have coilovers and can mash up/remove torsion casing.

meaning, you can still preserve the g50 box to slot directly into a 87-89 tub?

(i have both a 77 tub and a 88 tub... with 915 and g50 respectively)

[KTL]

Hey Frank,

Yep the hangup with the G50 in an earlier car is the trans is too long and runs into the torsion bar tube. Since you can't shorten the end of the trans where the interference occurs, the trick is to shorten the trans on the other end at the bellhousing.

But if you cut out the center area of the torsion bar tube, and appropriately reinforce the gap you make, you can fit the trans in there. Once you cut out the center of the t-bar tube, you've now killed the ability to install t-bars because that center has the female splines which capture the inner splines of the bars. So you're forced to run coilovers. Or at least that's what most people's solution is.

lite75 came up with an ingenious way of continuing to use torsion bars.

G50 conversion package

Has anyone put in a 993 G50/20 6 speed trans in a 78-88 930?

Verify a G50 is shortened?