911/01 transmission flange question

adam911 · 09-01-2010, 11:33 AM

I recently bought a replacement 1970 2.2 engine with 911/01 transmission for my car. On inspection I found a crack in the diff cover of the replacement transmission. On further inspection I found the differential to be broken into 2 pieces.

I have since sourced another 911/01 transmission. However on inspection I found the output flanges to be smaller than on my existing tranny. The original tranny flanges are around 120mm and the flanges on the replacement are only 95mm.

Is this unusal and what does it indicate about the replacement transmission?
Can I simply remove the flanges and provided the length and diameter of the flange shafts are identical, just swap them out from the old tranny?

Also, does anyone know a likely cause for the damage to the diff on the original tranny?

Any advice would be appreciated

Adam

Grady Clay · 09-01-2010, 12:12 PM

Adam,

I’m assuming that someone put other transmission axle flanges on the replacement 911/01. It may have been in a ’76-‘84 911 that has the 923 (912E) 100 mm CV joints. It is also possible that the transmission was made to fit a SWB with Lobro axles. If so, the flanges don’t fit the 911/01 differential. It is possible that these early (901/xx) transmission axle flanges damaged the 911/01 differential.

If there are no other changes to the transmission, you should be able to use the original 108 mm flanges from your original 911/01. If the differential is broken, be sure and inspect the flanges for damage where they interface with the differential and the ‘threaded piece’.

I recommend you inspect the replacement transmission for the ‘simplified differential’ update. The differential failure in your original transmission most likely is the ‘simplified differential’ failure. It would be instructive for the Forum for you to post images of the failure.

Search Pelican on “simplified differential” for the update.

Best,
Grady

adam911 · 03:40 PM

Grady,

Thanks for the reply.

Before I go any further let me provide you the transmission numbers;

Original transmission:911/01 - 7119087

Replacement transmission: 911/01 - 7113028

First off here is a couple of pictures of the original diff and damage. After reading the simplified differential threads imagine my surprise when I saw the original tranny had already had the upgrade.
Note the damage to the gear that meshes with the differential (is this the pinion gear?)

Here is a shot of the flanges. On the left is the original flange and associated stretch bolt and on the right is the flange and bolt from the replacement tranny.
Note only are the flanges a different diameter, but there's a difference in height also. However, the actual shafts measure the same length (56mm) and it is the flange itself that differs in length/depth. Also, looking at the bolt with the smaller flange it would suggest that this tranny has recieved the upgarde too.

Something else that's troubling me also is the person that supplied the tranny to me told me he took the side cover off in order to inspect the diff before he shipped the transmission to me.
I was under the impression that once the cover is removed one has to reset the end play. Am I correct or incorrect in this assumption?
By the way the new transmission is in the car, but hasn't been driven yet until I know I can simply swap the flanges over.

One other thing: on the replacement transmission when I turn one flange the other turns in the opposite direction. Does this suggest a limited slip diff?

Your thoughts would be most appreciated.

Adam

Matt Monson · 09-01-2010, 04:08 PM

Looks like Grady called it. That looks to me like an early 915 course spline flange.

That damaged gearface you have in your picture is the head of the pinion gear.

While I have only seen a few of these like this in recent times, I suspect we're only going to see more as the cars get older. It's become a major problem for 356 owners, even on cars that aren't driven hard. It's just age and metal fatigue on those cars, with them breaking at pin that holds the spider gears, just like yours did. Differential carriers have become a big money item in 356 circles. Thankfully 911 production numbers are so much higher there shouldn't be a shortage for many years to come.

But I don't think that's what happened here. I am suspicous that someone added those 915 flanges because they wanted to use the bigger CV joints because they were throwing some power at it. I've seen a few fail like this on v8 conversions. Yes, you are reading that right. People put v8's against 901/911/914 gearboxes with some regularity. It rarely ends well, but they do it anyway...

adam911 · 09-01-2010, 04:19 PM

Matt,
I was under the impression the larger flange is correct (standard) and the smaller flange is the anomoly, as the larger flange is what mates to my drive shafts correctly. In your post you write "early 915 course spline flange". So are you saying the larger flange is the early 915 course spline flange? Or the smaller flange?

Thanks

Adam

Grady Clay · 06:28 AM

Adam,

Yes, install the 108 mm flanges from your old 911/01.
That is the only flange ever used on a 911/00 or /01.
Be sure and inspect for damage.

The small flange is from a 914. That is good news because that fits the 911/01 properly.

Your original 911/01 was very late (9087) and was probably originally equipped with the ‘simplified differential’ update. You need to confirm that the replacement transmission (3028) has the update.

You do not have to reset anything when removing the differential side cover for inspection. It is useful to replace the lip-seal for the axle flange and the large O-ring around the side cover.

Hopefully the replacement side cover has as good clutch Bowden tube support ring as your old one.

The failure was not from lack of ‘simplified differential’ update. I would like to know more about ‘fatigue’ failure of these castings. Or … is there something that can show up with testing (X-ray, ZyGlow, magnaflux, etc.?) Porsche transmissions are too fine and expensive to have these failures if preventable.

Best,
Grady

adam911 · 09-01-2010, 05:40 PM

Thanks for the reply Grady.

Is it incorrect to assume that because the stretch bolts on the 914 flanges are the type without the teet, that the tranny has had the update?

Only the engine and transmission are in the car and I'm wary of getting any foreign objects inside of the diff housing.

Adam

Matt Monson · 09-01-2010, 06:29 PM

Quote:

Originally Posted by adam911

Matt,
I was under the impression the larger flange is correct (standard) and the smaller flange is the anomoly, as the larger flange is what mates to my drive shafts correctly. In your post you write "early 915 course spline flange". So are you saying the larger flange is the early 915 course spline flange? Or the smaller flange?

Thanks

Adam

Grady sorted it out and corrected my oversight.