Rebuild '70 911 trans or replace with 915?

911-m5 · 11-14-2005, 02:12 PM

My 911 tranny is a 4 speed which I kinda like, but I have never tried a 5 speed out. Is there a big difference? I guess my options are really: rebuild my 911 4 speed, buy a 911 5 speed or a 915. Any opinions? And yes I have searched and found some info, but nothing that has really helped me pick a direction.

Thanks,

Allan

911-m5 · 11-14-2005, 04:37 PM

No opinions? wow.

randywebb · 11-14-2005, 04:47 PM

the 915 is heavier, stronger and has a worse shift pattern than a type 911 trans. You might need to clearance the tunnel with a hammer.

klaucke · 11-14-2005, 04:50 PM

Some people (racers included) claim the 901/911 transmissions are smoother shifting and like their action. Some, like Randy Webb, have actually backdated from a 915 to 911 (or 901, I forget).

Personally, I like the dog-leg pattern, which hearkens back to the days of pure sporting heritage, and is unique. I vote rebuild your 911 or update to a newer 5 spd 911.

You may be able to rebuild and change the internals to make your box a 5-spd, I'm not sure if this is possible but it seems logical. I would hazard a guess that there are a lot of 901 parts out there, due to the trannies use in 914's. I see whole 914's for sale for a couple hundred bucks, perhaps its as easy as swapping the nose cone and ring and pinion.

Erik Mckenna · 11-14-2005, 04:57 PM

Will a 901 bolt up to a 78 SC motor with out any issues? I am having some tranny issues with my 915.. can I use a 901 on my car until I get the 915 sorted out? or will it not mate up with the 3.0?

-Eric

randywebb · 05:07 PM

Eric - I think so, but mine was 911 onto a 3.2L. Kennedy & Patrick make adapter flywheels - be sure to check it for balance. Be sure the CV's match - they may not for a 901. Figure out when they cahnged the flywheel/crank bolt pattern... that's your answer as to mods.

m5 - I agree w/klauke re getting a 5 speed type 911 trans. Scott Clarke is rebuilding his 911 trans right now, so check out his threads. Grady knows these things inside out, and has numerous threads/posts if you search.

Figure out what special tools you'll need and start looking for a 5 speed.

The idea re using 914 parts is a great one - I had no idea they were that plentiful & cheap.

You can swap gears to get exactly the ratios & spacing you want so investigate that. I have never rebuilt one, I just modified a 911 one to work in my '73 car with 3.2L engine. Your task should be conceptually easier, but might require more detail work. Be sure to search for simplified + differential...

rudy · rudy's Garage

I used a 71 911 trans behind a 3.0 and it worked fine. I prefer the 911 over the 915.

randywebb · 11-14-2005, 05:06 PM

one mo' thing...

if you are in heavy stop & go traffic a lot, then the 915 shift pattern would be better. But if that is the case, then you shouldn't be wasting your 911 anyway...

klaucke · 11-14-2005, 05:41 PM

Randy, I'm not sure that is the case re: stop and go traffic. Unless you have to completely stop, you can leave the car in 2nd no problem. With my 915 w/ 7:31 R&P I stay in 2nd whenever I'm in traffic, I'm just always rolling at least a tiny bit.

Todd Simpson · 11-14-2005, 05:47 PM

I never found the 1-2 shift tough in a 901. Just shove it forward and the springs take it to second. This was both before and after a Fairbanks rebuild. Cranky 915 second gear synchros have caused me more headaches.

My car had a 901 (911) for years and went I went to a 3.2 I put an early 915 in. Unless you have a need to handle more torque I say find a 5 speed 911.

Scott Clarke · Scott Clarke's Garage

Someone in the classifieds has a type 911 5 speed for sale. I'd snag it. You will have closer ratios with a 5 speed. You will like the difference. Be sure to see the recent threads concerning "simplified differentials." Parts to fix the problem with the simplified differential can be purchased new for reasonable cost, probably from our host.

I'm not sure what ratios the 4 speeds had, but you might be able to part out your old box. The gearsets may be of use to racers, or even to me!
-Scott

Edit: Looks like you should have a A,HB,S,ZA. 5 speed is A,GA,O,V,ZA. So, the 5 speed has much closer ratios. That S you have is desirable for close ratio 5-speed boxes.

911-m5 · 11-15-2005, 01:59 PM

Thanks for the info guys. So 911 5 speed it will be.

Scott - I didnt see it in the classifieds. I looked through the first 4 pages or so...

Also, if i wanted to put the "s' in the 5 box which gear would it replace?

Thanks

Allan

Scott Clarke · Scott Clarke's Garage

Allan-
Do a search in the classifieds for "911 gearbox." The seller is in Indiana, and the ad has lingered for a while now. The "S" would be fourth, but you'd need a F input shaft/second gear, a M third, and a W,X, or Y fifth. The earlier 901 boxes had A,F,M,S, and X. The 2.2 cars had taller gears for a more relaxed driving experience.
-Scott