Porsche Transmission Questions

[Clay]

I have a couple questions about the porsche transmission. I noticed many gt40 setups use the porsche transmission, my question is, is there a certain year porsche you have to stick to?
Could you use an older porsche transmission?
Are there adapter plates for older porsche transmissions?
If not, Do any of the older porsche transmissions have the same bell housing bolt pattern, therefore allowing the currently available adapter plates work. OR are the bell housings interchangeable between the old and new porsche gear boxes, therefore allowing the currently available adapter plates to be used?
Do all the porsche transmissions use that rod to shift, that ends up sticking out the back when oriented for a gt40?
Can you buy the shift assembly seperately that allows shifting of this rear rod type setup? If not, does anyone have detailed drawings or pictures to aid in making one from scratch?

and lastly, can anyone explain the way a porsche transmission shifts? I see the rod, but that rod couldnt possibly complete the task of selecting each and all of the gears could it? (unless maybe it turns radially and moves in and out or something), i would imagine that rod does forward and backward motion while some other shifter lever toggles between shift rails.


also, i searched for "porsche transmission" in all forums and didnt find what i was looking for before I made this post. I apologise if I asked questions that have been answered before.
thanks in advance
clay

[Tim Kay]

Welcome Clay,

I’m pretty new to the adaptation of a Porsche gear box myself but FWIW here’s a bit of what I know:

Your best off selecting the ‘G50xx’ gear box and more specific G50-50 or G50-52. I believe most come from late ‘70s Carrera and Turbo 911’s.They are a 5 speed configuration and have the strongest gear sets and ring & pinion with a heavier side plate. Gear ratios suit the V8 fine and are very similar to the ZF’s. Some come with limited slip or they can be added. You can upgrade them to steel syncros, billet shift forks, ect. Short nose covers can be installed as well as side shifting units for cable shifters. The case must be inverted which will allow the lowest c\g attainable for the motor.

In addition, try searching under “G50” or “Transaxle”. There is plenty more to read [img]/ubbthreads/images/graemlins/shocked.gif[/img] [img]/ubbthreads/images/graemlins/smile.gif[/img]

[Clay]

[ QUOTE ]
Welcome Clay,

I’m pretty new to the adaptation of a Porsche gear box myself but FWIW here’s a bit of what I know:

Your best off selecting the ‘G50xx’ gear box and more specific G50-50 or G50-52. I believe most come from late ‘70s Carrera and Turbo 911’s.They are a 5 speed configuration and have the strongest gear sets and ring & pinion with a heavier side plate. Gear ratios suit the V8 fine and are very similar to the ZF’s. Some come with limited slip or they can be added. You can upgrade them to steel syncros, billet shift forks, ect. Short nose covers can be installed as well as side shifting units for cable shifters. The case must be inverted which will allow the lowest c\g attainable for the motor.

In addition, try searching under “G50” or “Transaxle”. There is plenty more to read [img]/ubbthreads/images/graemlins/shocked.gif[/img] [img]/ubbthreads/images/graemlins/smile.gif[/img]

[/ QUOTE ]

So stick to the 70's G50xx transmissions?
When you said it must be inverted, you mean put behind the engine and turned upside down right? just clearing up terminology.
Side shifting is for shifter cables? wasnt side shifting a stock feature in some of the porsche transmissions?
Also what do you mean by "Short Nose Cover"?

[Tim Kay]

Someone may correct me here, but I 'think' the late 70's is when the G50-xx were built.

Correct, 'inverted' is turn upside down (nose to tail).

'Short nose cover' - taking the original cover and modify it by shaving off excess material not necessary for a GT40 application. If space is limited you can gain an inch or more.

As far as adapter plates go, that's my next venture. My understanding is 'Powerhaus' and\or 'Kennedy Eng' have or can adapt just about anything.

[Tim Kay]

I stand corrected on the production date of the G50 (1989 thru 1994), I researched a bit and found the following:

Check this link

[Clay]

thanks, that post has lots of usefull information that answered a lot of my questions!

now i just need either some drawings, pictures, or a detailed description of how this shifter arm works...
http://www.locostbuilders.co.uk/view...823&pid=210160

[dave harris]

The shifter arm "rotates" for your neutral gate travel, and goes in/out for the gear selections. Each car Mfg. does it different, but the DRB (GT40 Australia) cars use a shift rod for the rotational motion (neutral gate) and a Morse cable for the in/out gear selections.

Clear as mud yet?

cheers

[Phil]

Clay
I can answer some of your questions.
The shift rod on the trans is oriented in normal use to the front of the trans...this is the configuration of most of the Porsche vehicles (the 914 having the gearbox behind the motor is the exception.
The older transmissions 915 & 930 need to have the ring gear flipped inside the case to give the correct rotation. The 915 box is a 5 speed and although strong, not as good as the G-50. I believe the 915 box had a 8/33 ring and pinion and a .83 overdrive in 5th gear. The 930 box is much stronger, a little harder to find, but it is a 4 speed, I am not sure of the ratios on that one. There was a company called Vallios that made a side shifter arrangement for these boxes that bolted onto the cover plate under the trans. The G-50 box is definitely much stronger, but the ring gear cant be flipped because of space limitations inside the box, it must be run inverted which raises the half shafts about 5" on the inboard side. I don't know if there is a side shifter kit for this trans. The only other box I have experience with is the 914, this box is a side shifter box from the factory, but I wouldn't expect it to hold up against a V-8, also the clutch is rather small.
I think Kennedy Engineering still has adapters for all of these porsche transaxles.
Hope this helps
Phil

[Eric]

I have actually built a side shifter setup for my 6spd g50. Fairly simple so far but not 100% complete yet. The "nose cone" that people are referring to is the furthest part from the clutch, there are 2 options, the earlier g50 has the desireable nose cone, the later ones have a mount as part of the tail housing that can be cut off. Also, I think 90 or 91 and up need some minor bellhousing machine work to clear the starter that is used for the V8. I have also modified mine to use a standard ford bellhousing and starter and clutch. Not worth the effort for a 5 spd but the 6 spd is longer, I am after every inch I can get.

[Russ Noble]

[ QUOTE ]
The older transmissions 915 & 930 need to have the ring gear flipped inside the case to give the correct rotation.

[/ QUOTE ]


This is only if you don't flip the trans. Flipping the trans saves all the hassle and also gives the more desirable lowered engine position. The 930 is the strongest of all the P trans and is reputed to reliably handle 700hp.

Clay. As previously stated a diligent search of this site will provide answers to more questions about Porsche trans than you would ever think to ask. It'll take a while to extract it but it's all there.

Regards

[Clay]

[ QUOTE ]
The shifter arm "rotates" for your neutral gate travel, and goes in/out for the gear selections. Each car Mfg. does it different, but the DRB (GT40 Australia) cars use a shift rod for the rotational motion (neutral gate) and a Morse cable for the in/out gear selections.

Clear as mud yet?

cheers

[/ QUOTE ]

dave, im pretty sure i understand everything except the in/out motion with the cable. I cant visualize how that works.

[dave harris]

Picture a standard bicycle hand brake cable - It's designed for a single direction (Pull) motion. A Morse cable is just like a brake cable on a bike, except it's MUCH thicker and made to withstand both the pull motion and a push motion. So the shift lever's forward and backward motion is translated in the Morse cable to a Push/pull at the transmission shift rod.

Any clearer?

cheers

[Tim Kay]

G50-52, side shift, G50-50 bell housing, ring gear oiler & shorten nose piece:

[Tim Kay]

& close up:

[Eric]

Wow, all this time I thought I was stupid for cutting a hole in the side of my tranny, my side shift setup is almost identical to that, who sells it and how much?? Like to know if I bother finishing mine or not.

[Lynn]

Tim,

Come on, don't keep us in suspense! Where did you find this jewel and where can we get more info, PLEASE!

Are the initials CMS or GMS ??

Regards,
Lynn

[Tim Kay]

Sorry guys, forgot to get back to you [img]/ubbthreads/images/graemlins/crazy.gif[/img]

It's stamped "CMS". That's all I know.

Bobby Hart at California Motorsports in Lake Havasu City, AZ did the complete rebuild on the G50 and that is the shift unit he attached. For more info he would be happy to fill you in, very nice guy. It may even be proprietary, I don't know.

Bobby can be reached at: 928-855-5755 (no web-site avail)

[Lynn]

Tim,

Well that matches: "C"alifornia "M"otor "S"ports

Thanks very much! I'll give Bobby a call tomorrow!

Regards,
Lynn

[Eric]

Any news on that shifter Lynn?