915 to 901 backdate

[Shuie]

I’ve seen a bunch of threads about swapping a 915 in a 901 car. How about backdating a 915 car to use a 901?

Car is a '72 and is void of engine and transmission at the moment. Engine plans are a way off, but I want to keep this one under 3.0. I know the 915 wasn’t standard in '72 and I’m not sure if this car had a 915 or a 901 in it originally. How do I tell what gearbox it had originally? Assuming it had a 915, how difficult of a project would it be to convert it to a 901?

CV's, shift rod, clutch cable, clutch, trans mount, and shifter all come to mind as things that could potentially be different, but I keep telling myself that most of this stuff is probably the same since both gearboxes were used in the 911 in '72.

What about the core gearbox? Which one should I use? Al or Mg case? I know about the dreaded input shaft issue on a '72 915, is there a similar situation to try to avoid when choosing a 901?

What about upgrades? I’ve seen a great thread where Tyson talks about flipping a '73 shifter housing around and rewelding it for use on a 901. It made my head hurt trying to picture what he was explaining but I’m sure it was genius and would work great. What else can be done to improve 901 shifters, linkages, etc?

TIA

[randywebb]

I've done it. It takes a while - but should be easier for you since we can walk you thru it and you won't have to research everything like I did. Use a type 911 trans. not a true 901. i.e 1970-71 MY's. You will need to relocate the pivot ball for the shift fork - and do so precisely. You need to saw off a tang on the housing BEFORE you put it in the car - if you have the hard oil line that is hoop shaped on your engine. You need to change the push clutch to a pull one -- or was that change the pull clutch to a push one?? You need the shift fork for that too. You need the shift rod from the earlier cars too - I think Tyson posted on that.

When are you planning to do this? My time is limited for the next month (busy attacking the gummit) but I'll have more time later to search out pics and etc. I do have a good bunch of pics from when I did this - but they are not organized too well. Also, Grady surely knows how to do all this just out of his head.

"great thread where Tyson talks about flipping a '73 shifter housing around and rewelding it for use on a 901."
- recall where that one was??

I'm not sure what flipping & welding means. But you want to use the last of the 915 shifters if you can -- 1985 & '86 I think -- Bill V. posted the cite to the Pano article on that a while ago. The Pano article discusses all the improments in the shifter over the years but doesn't really say what the last improvement was tho.
Other than that, you just replace all bushings and rebuild the puppy as in Sherwoods's article.

Steve Weiner has posted on the Al int. plate and maybe some other items to strengthen these boxes up. You may not need the 904 shaft - depends on use. Search both here and Rennlist. Obviously, you won't want to go dragging Mustangs.

You can start doing some searches and compile the threads. That will get you started. It could make a nice tech article or at minimum, an organized thread.
So the names to search on will be mine, Bill V's, Grady, Steve W., ad Tyson + the topical terms for whichever sub-task you are researching.

Have fun - it is a great shift pattern and saves some wt. too.

[darkbeer]

would it be easier & cheaper to just put a 901 shift knob on the shifter???only you will know for sure!!!


(please...you know I'm just kidding)

[Shuie]

Thanks Randy. I appreciate the help. I wont be doing this for a while.

Here's the thread where Tyson mentions flipping the R-5 lockout mechanism on a type 915 shifter so that it can be used as R-1 lockout. Pretty smart. I never would have thought of that on my own.

901 vs. 915 trans.

[randywebb]

Ah - the lockout. Now I understand.

Some info is out there already in various threads (see above). Just renew this thread when you're ready for the pics and etc.

[PcarPhil]

Randy,

Can you post the pics you have on the 915 to 911 trans backdate?

I've got an 80SC and a 71T sitting in my garage with crazy thoughts of backdating the '80 while I work on rust repairs on the 71 chassis.

Shuie - Did you end up installing the 911 trans?

Thanks for the info,
-Scott

[randywebb]

I've already posted them - just search on the key terms.

You can do the '71 trans in an SC - you will need an adapter flywheel from Kennedy or Patrick - be sure to check the balance - mine was way off.

[randywebb]

PS - one thing often neglected is the shorter shift tube for that trans - you will need to get one. I think Tyson mentioned that to me.

[PcarPhil]

Randy,

I did a search and read up on yours, Grady's, and others posts on this trans backdate.

If I did this I'd be using a '71 911 trans and mount it to my '80 3.0 engine. Since the trans is a '71 911 (not a 901), will I still need to relocate the pivot ball for the shift fork?

From what I read I don't think I'll need to.

Thanks for the help,
-Scott

[randywebb]

No, I think you DO need to. I did (on a 3.2L) but I also swapped the thing over re push/pull actuation. I posted a thread on this back when. Probably 2 years ago.

Grady will know for sure.

Also, check out the threads on updating that ball head - I'm not sure but if I interpreted Grady's comments correctly, then that should be changed to the hex head type arrangement.

Other items that float to the surface of my mind:
- check fork for cracks, places it was ground before, wear marks
- use a hi-temp, high pressure, sticky grease
- cut a groove in the tube as Grady noted - for any grease drips
- Scott Clarke has the part no.s for eliminating the simpl. diff. and should post them soon


also:
http://forums.pelicanparts.com/porsche-911-technical-forum/260246-upgrades-type-911-transmissions.html#post2346205

Post again and I'll try to dig up some pics of when I did this...

[911pcars]

FWIW, before I knew there was a difference in shift tube lengths, I used the existing 901 shift tube with a 915-5 speed. It works fine. YMMV.

Sherwood

[Jared at Pelican Parts]

Perhaps Im not thinking it through, but why would you want to do this? Just to have the dogleg?

I wish I could have had a 915 in my old 914.

[jkarolyi]

>I know the 915 wasn’t standard in '72

Your '72 DID come standard with a 915! Well, actually the four-speed version of the 915 was standard, but 99% of '72 911s came with the 5-speed 915.

The '71s and earlier had the 901 with the dogleg first gear. Well, actually (here we go again) the '65-69 had the magnesium case 901 and the '70-'71 had the aluminum case "911" transmission.

I would stick with a 915 since it's original. You guys got so excited about backdating to a 901 that you didn't inform Shuie of his error. Shame on you guys.

[randywebb]

yeh, shame on me. you can pay for beer tonite & that will shame me even more...
{great sig, BTW... esp if you practice "long fist"}


"Just to have the dogleg?"
- Yes, or to put it a bit differently, to have the inline 2nd to 3rd shift. And to reduce the wt. of the car a bit. Those are my reasons.

[rw7810]

Couldn't resist. There sure is allot of misinformation kicked around on Tranny's. Grady Clay seems to be the most authoritative on subject. Anyway, the 70-71 trannys were/are magnesium. I got one siting on my garage waiting on a seal so i can button it up after a 1st gear synco repair.

Randy - where can I get some of this?? " use a hi-temp, high pressure, sticky grease" Any brand names??

[jkarolyi]

Whoops! I mixed them up...'70-71 mag case, '69-earlier aluminum case.

>{great sig, BTW... esp if you practice "long fist"}

Thanks.

[randywebb]

hi-temp, high pressure, sticky grease... I used some Bosch dist. grease -- again, ask Grady what he thinks. He should see this & post...

sticky 'cuz you want it to stay there and not flow...

[PcarPhil]

Originally posted by Jared Fenton
Perhaps Im not thinking it through, but why would you want to do this? Just to have the dogleg?

I wish I could have had a 915 in my old 914.

I'm not sure at this point that I will do this. If I did, here's why:

1. I prefer the 911 (901) shift pattern.
2. I prefer the 911 gearing for my street car.
3. Lighter weight.
4. My 911 trans shifts well with my Rennshift shifter.
5. I've got most, if not all, of the parts needed sitting in my garage. If I didn't like it I could swap back to the 915 trans.

If it turns out I'd have to modify (welding, cutting, etc.) the 911 trans to work with my 3.0 then I won't do it. For now.

-Scott