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

[rgalla9146]

You've got the idea right and the parts to do it.
I did the same years ago but never installed it in my car.
I had someone flip the '70-'71 911/01 R&P and assemble the trans with the 914
side shift console and rear cover.
I'm not sure about the clutch cable but I think a certain OE 911 works.
Probably 70-71
The 911 box has a special flange as part of the casting that the end of the cable
attaches to. Clutch adjustment is by length of Bowden sleeve.
I ended up doing a Martin Bott 916 conversion behind a short stroke 3.2
Just getting to drive it recently.
I ended up selling the 70-71 parts

[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

[mepstein]

Problem I think about is you need two trans to make one. An early 911 trans core is usually $1500, mare if it’s in good shape. Then you need to rebuild the parts from both into one trans.
Why not just use the stock trans, buy the clutch conversion kit from KEP for ~$650 or whatever the going rate these days and call it done?

[sixnotfour]

Problem I think about is you need two trans to make one. An early 911 trans core is usually $1500, mare if it’s in good shape. Then you need to rebuild the parts from both into one trans.
Why not just use the stock trans, buy the clutch conversion kit from KEP for ~$650 or whatever the going rate these days and call it done?

(IMG:style_emoticons/default/agree.gif)
old school cool...but not worth the effort..IMHO.. at this point in time..

I have several , early all aluminum pressure pressure plates,,
and 911/01 boxes
But if you drive hard the anti rotation strap locations will break.. (IMG:style_emoticons/default/popcorn[1].gif)

And its still a 901..

[Montreal914]

914World, the best! (IMG:style_emoticons/default/smilie_pokal.gif)

So, the decision point between using the 901 (whichever version) and the 915 (916) was based on these factors. BTW, this is for a narrow body street application.

What I have in hand:
- 3.2 with its stock clutch
- 3x 914 side shift gearboxes
- 70-71 901/01 (potentially a 71 since it has the extra casting underneath for the # and serial)
- 1977 915/61 aluminum box w/electronic speedo


915 Pluses/Minuses:
+ Strength
+ Better ratios (5th from a later box would be best)
+ Plug an play with 3.2 clutch/flywheel
+ Output flanges 100mm (perfect for my 944 CV setup)
- Weight
- Shifting pattern (no dog leg (IMG:style_emoticons/default/dry.gif) )
- Shifting feel (I hear different things on this (IMG:style_emoticons/default/confused24.gif))
- Expensive Martin Bott kit
- Ovaling of the bearing saddle at the pinion end? (Needs welded upgrade and 930 bearing, cost)

901 Pluses/Minuses:
+ Lightness
+ Dog leg (914 caracter)
+ I have already made my double support side shift console and work great
+ I have many gearboxes in hand to pick the best parts out off
+ It can use the pull clutch (with my 70-71 911 case)
+ 70-71 911 box has 914-6 ratios (A-GA-O-V-ZA), I plan on using AA-GA-O-V-ZD
+ Simple clutch cable setup (no chassis stress)
- Week 1st gear (cantilevered)
- Thought I could plug it directly with the 3.2 pull clutch, but no.
- Expenses needed to flip R&P
- Expenses for: 100mm output flange, release bearing, 71 clutch, other...

The overall cost is also a big factor. I will have to go back to my spreadsheet and redo some calculations due to more components involved in the 911/01 use.

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@ClayPerrine :
Thank you for providing all of these very detailed instructions! If I go that route, I will precisely follow all of these instructions. (IMG:style_emoticons/default/pray.gif)

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

"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."

- Since this is 100% pull, the end of the cable sleeve does not need a stop, right? So some kind of nice P-clamp to hold the cable would do?

- Vent: I did notice that difference and wondered. Thank you for the instructions to work around it.

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@mepstein :
Yes, I could do the KEP mod too. I was concerned by a comment @Steve posted on a while back sharing his experience with the KEP setup.

This: http://www.914world.com/bbs2/index.php?s=&...t&p=2254465

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@sixnotfour :
What is that anti-rotation strap you are referring to in this comment?
"But if you drive hard the anti rotation strap locations will break.."

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Thanks guys for sharing the knowledge/experience. (IMG:style_emoticons/default/pray.gif) (IMG:style_emoticons/default/pray.gif) (IMG:style_emoticons/default/pray.gif)

[mepstein]

I haven’t noticed the clutch issue that Steve mentions but I haven’t driven my car nearly as much as him. I have an aluminum box with a Wevo kit that was built by Peter Dawe. I’m planning on using that with a 3.4 in my GT car. I would love to find someone who bought the Martin Bott kit and build up a 916 box. If anyone has a kit that has gone unused, please contact me.

[ClayPerrine]

The Kennedy Engineering kit just adapts the 3.2 factory flywheel to use a 914 clutch. You get a more powerful engine, but the same clutch assembly as a 914-4.

The clutch from a 914 is 215mm in diameter. The clutch from a 70 911 all the way through a 3.2 Carrera is a 225mm clutch. You get more clutch meat with the pull type clutch.

The only thing I don't like about the 70-71 911 transmission in a 914 is the fact that the throwout bearing is very expensive. Everything else is great!

[Steve]

My experience…
3.2 with KEP adapter and stock 914 trans.
-Uses stock 3.2 flywheel and has special bolt on ring that adds 228mm bus clutch. They recommend there stage 2 kit.
-This clutch is harder to push than stock.. Some people have no issues with it. I also have a v8 914 that uses a stage 3 clutch which is even worse than the stage 2. I am also selling the v8 car and that is one of the reasons I am selling it. Note KEP also sells a 228mm flywheel instead of the ring that also works with there clutches.
-If it’s a stock 3.2, 1st is worthless and 2nd is too tall to use as first without slipping the clutch. Not a problem with a hopped up 3.2, 3.6 or v8.
My current setup I used with my 3.2. All stock 915 trans for a 3.2 with Martin Bott 916 kit. Clutch is super easy to push. Like butter. There is a return spring on the pedals and an omega spring on the trans. Also the gearing was designed for the 3.2 so all gears are amazing in town and on the freeway. Downside it’s super expensive.

I was also planning ahead with the 915 trans for future 3.6. I recently finished the 3.6 and sold the 3.2. The 3.2 was awesome with the 915 in a 914, but the 3.6 with a 915 box is beyond amazing.

[Steve]

Clay is running a boxster/cayman trans with his 4.0 motor. If they ever come out with a kit for the 3.2 or 3.6, this would be the way to go over the 915 trans. The newer borg warner design is way easier to shift than a 915 or 914 trans. I’m happy with my 915 trans and have no interest in converting to anything else.