70-71 911 box for 914-6 conversion, Looking for confirmations... Options

[Montreal914]

I was on the fence between using a 915 or a 901 style box for my 3.2 six conversion until recently where I read a comment from @ClayPerrine that the 70-71 911 (911/01) box was set up with the pull style clutch.

What I have in hand for my conversion:
- 911/01 box
- Three side shift 914 gearboxes
- Various gear set ratios to have fun! (IMG:style_emoticons/default/driving.gif)
- 100mm coarse spline output flanges to go with my 944 CVs

My plan was to use:
- Stock 3.2 flywheel clutch assembly currently on the engine
- Get a 70-71 release bearing
- Get a 72(?) clutch cable that would be straight pull (no cable pulley)

I was going to use the 911/01 bits, flip the R&P, reset the pinion depth, use complementary 914 side shift trans cover, shifting, etc

What I think I am undestanding from this thread linked below is:
- The pull clutch setup works well
- Yes, it can be tricky to get the release fork mating to the bearing upon assembly
- I should not use the 3.2 PP as it will pull the fork pivot bolt?
- I should use a 2.2 PP?
- What disk should I be using?
- Does this simply bolts on the 3.2 flywheel?
- Is the clutch pivot shaft/arm at the pedal cluster different than 914, should I replace it? I just rebuilt my pedal cluster.

Any inputs appreciated (IMG:style_emoticons/default/beerchug.gif)

http://www.914world.com/bbs2/index.php?sho...267204&st=0

[ClayPerrine]

I was on the fence between using a 915 or a 901 style box for my 3.2 six conversion until recently where I read a comment from @ClayPerrine that the 70-71 911 (911/01) box was set up with the pull style clutch.

What I have in hand for my conversion:
- 911/01 box
- Three side shift 914 gearboxes
- Various gear set ratios to have fun! (IMG:style_emoticons/default/driving.gif)
- 100mm coarse spline output flanges to go with my 944 CVs

My plan was to use:
- Stock 3.2 flywheel clutch assembly currently on the engine
- Get a 70-71 release bearing
- Get a 72(?) clutch cable that would be straight pull (no cable pulley)

I was going to use the 911/01 bits, flip the R&P, reset the pinion depth, use complementary 914 side shift trans cover, shifting, etc

What I think I am undestanding from this thread linked below is:
- The pull clutch setup works well
- Yes, it can be tricky to get the release fork mating to the bearing upon assembly
- I should not use the 3.2 PP as it will pull the fork pivot bolt?
- I should use a 2.2 PP?
- What disk should I be using?
- Does this simply bolts on the 3.2 flywheel?
- Is the clutch pivot shaft/arm at the pedal cluster different than 914, should I replace it? I just rebuilt my pedal cluster.

Any inputs appreciated (IMG:style_emoticons/default/beerchug.gif)

http://www.914world.com/bbs2/index.php?sho...267204&st=0

You MUST use the 2.2 pressure plate,throwout bearing and starter ring gear. The pressure plate will bolt to the 3.2 flywheel without any adapters. Using any other pressure plate will pull the clutch fork pivot bolt out of the transmission case, taking the threads with it. Also, you can't just use a 914 transmission and redrill the location for the pivot bolt. The 70-71 911 transmissions have a top hat shaped steel insert that has the threads for the pivot bolt in it. Without that insert, you end up pulling the threads out of the magnesium transmission case. Now if you completely tear down your 914 transmission and have the insert installed, it will work. But it's easier to just get a 70-71 911 transmission.

So to do this, here is what I recommend for parts, starting from the clutch end and working backward.

1. Stock 3.2 flywheel.
2. 70-71 911 clutch disk.
3. 70-71 911 pressure plate.
4. 70-71 911 throwout bearing (very expensive these days).
5. 70-71 911 transmission case.
6. 70-71 911 clutch fork and pivot bolt.
7. Your choice of gear ratios.
8. Billet aluminum intermediate plate.
9. 914 side shifter rods.
10. 914 side shifter tail cone.
11. 914 side shifter console.

You will also need the clutch cable from a 76 911, and you have to make a bracket to support it at the transmission end.

There is a tab on the bell housing end of the transmission that is the anchor point for the clutch cable in the 911. You have to cut it off to provide clearance for the clutch cable to work properly. You can leave a nub and use that to mount the cable support.


The gear stacks are identical. I suggest you figure out what gear ratios work best for you. I ran this setup behind a 2.4 MFI motor and I used A - F - flipped ZD - S - ZD for the ratios. The flipped ZD got me really close to the correct RPM droo from second to third, and the ZD fifth kept me from overheating the motor at 60 MPH. I first had a flipped HB in 5th, but I took that out because the oil temp would go through the roof at 60 mph. I could run 50 in forth all day, and run 75+ in fifth without overheating, but to stay at 60 for long stretches would overheat the motor.

There is a vent on the top of the transmission case that has to be moved to the same location as the 914 case. If you don't move it, the spinning ring gear on the differential will throw all the gear oil out of the case through the vent. Just use a pipe plug to close off the existing hole, drill and tap the hole in the 914 location and install the vent at the proper angle per the 914 manual. The 911 uses a different angle for the vent because the airflow over the transmission is coming from a different direction.

Make sure to buy a manual that covers the 70-71 911 clutch setup. There is a steel spring that goes between the clutch arm and the case to push the fork back against the throwout bearing (#4 below). Don't leave it off. It has to maintain pressure on the arm or the ears on the throwout bearing will rotate and disengage from the fork. Then your clutch doesn't work.

Also, installing the transmission is better done with the engine and trans out of the car. The clutch fork is bolted to the transmission case, and then bolted to the engine. Next you have to stick your fingers in the holes in the top of the transmission case and rotate the throwout bearing until it engages with the clutch fork. This is a MAJOR pain in the butt.

The upside to all this is you never have to worry about the clutch tube tearing out of your chassis. There is absolutely no load on the tube at all with this setup. You can toss the clutch cable pulley and mount.


While it works great in a 914, this setup was a stop gap until the beefier 915 transmission came out. With the 915 transmission, you can use a 3.2 pressure plate and throwout bearing, and the 916 Martin-Bott style kit now available works well in a 914. Personally, I don't like the way a 915 shifts, and the dogleg gear pattern just feels right in a 914. Despite the ridiculous price for the throwout bearing, I would still run this setup in a 914.





More info:
https://forums.pelicanparts.com/porsche-914...14-gearbox.html

Martin-Bott kit for the 915:
http://www.914world.com/bbs2/index.php?showtopic=102988