The definitive : '69 Transmission in a '70+?

[YTNUKLR]

I have a 50% chance of being able to do this: one friend said it is possible and another said I would need custom axles.

Of course, the clutch is a "push" 215mm on a '69, and "pull" 225mm on a '70, but it seems like, other than that, this would work.

Letting curiosity get the better of me...

[davep]

If it was a magnesium case 1969, then the clutch would likely be the only issue; don't forget the pivot point change. Drive flanges are another issue. Do you have the serial # & type # from the '69?

[Grady Clay]

Scott,

You will find a lot of this (and more) on Pelican.

Yes, the ’69 and ’70-’71 CV joints and axle assemblies are the same.
If your ’69 901/xx transmission has its original axle flanges, they will bolt-up correctly to your ’70 axle assemblies.

The difficulty comes if you try and mix a ’69 and earlier 901 differential with ’70 and later flanges that fit the 911/915/930 differential (and vice versa).
The BIG problem is that they fit, just not correctly.
There are even more significant differences if we are using ZF LSD flanges.
I used to have all these measurements.
I’ll see if I can find them.

The ’69 transmissions have the ball-pivot for the clutch arm positioned for the 215 mm push-type clutch.
No issue there when you use the 1969 and earlier 215 mm clutch.
The only issue here is there is not the oblong boss for the clutch arm pivot pin, allowing a ’69 901/xx to be converted to pull-type clutch without welding on the main casting.
Converting a 911/xx from 225 mm, pull-type clutch to 215 mm push-type ‘only’ requires machining and a threaded insert.
I have several 911/xx with ability to have either pivot.

The ’69 transmissions will also have the proper retaining ring for the push-type Bowden tube.
You will need this Bowden tube and a ’69 clutch cable.

Something to consider; in ’69, the clutch lever arm at the pedal assembly was longer than in ’70-’71.
If you maintain this ’70 part, you will have less force and longer throw than if you use the ’69 part.
The other way around is to always use the longer arm, allowing faster operation of the clutch.

The clutch release (TO) bearing guide tube is longer on the ’70-’71 type 911 than on all the earlier type 901.

The best push-type link between the cable and arm (“plastic piece”) is a steel ‘wedge’ type.
Carefully make clearance between the arm and the link at the corners of the ‘slot’ in the arm.

You will have no problem with your 2.2 engine oil hose that goes over the transmission.
Problems arise when you use the early ‘under-the-transmission’ hose-pipe assembly with the 2.2 pull-type clutch linkage.

The aluminum case 901/xx transmissions do not use spacers between the nose casting and the transmission mount.
The magnesium case 901/xx uses unique-to-‘69 spacers.

The mag case 901/xx have an issue with cracks in the main casting.
These are above and outboard of the input shaft roller bearing.
They appear to be related to the steel insert bearing retainer.
There is commonly some minor oil leakage.
I have never seen this cause a mechanical issue.

Other things like back-up light switch and shift linkage aren’t an issue.



For reference, the transmissions involved here are:
For 1969.
901/04/06 alu 4-speed.
901/05/07 alu 5-speed.
902/14/16 alu 4/5-speed.
902/50/60 alu 5-speed specials.
901/75/76/77/78/79 alu 5-speed specials.
and
901/12 mag 4-speed.
901/13 mag 5-speed
901/16 mag 6:29 912 5-speed.
901/80/81/82/83/84 mag 5-speed specials

Compared to the ‘70-’71 transmissions:
911/00 mag 4-speed.
911/01 mag 5-speed.
911/80/81/82/83/84 mag 5-speed specials.

There are more.

If someone finds an error or extension with this explanation, please post.
Accuracy is critical and I'm no longer perfect (as I'm no longer a teenager).

Best,
Grady

[YTNUKLR]

Grady, thank you so much. I knew it was all over Pelican, I am sure you have explained exactly this thing a thousand times over, but I think the search engine has a difficult time with some combos like "'69" and "901/07" etc. . .

[nimbels]

HI Grady,

I seem to have a weird transmission (number) compared to you list.

I have a (69) G901/12 (71900018) transmission, but it's an Alu instead of mag Case and it's also not a 4 speed but a 5 speed...

I guess since it's one of the first LWB car's this could be a fluk in the numbering style maybe??

Kind regards, Maarten

Scott,

You will find a lot of this (and more) on Pelican.

Yes, the ’69 and ’70-’71 CV joints and axle assemblies are the same.
If your ’69 901/xx transmission has its original axle flanges, they will bolt-up correctly to your ’70 axle assemblies.

The difficulty comes if you try and mix a ’69 and earlier 901 differential with ’70 and later flanges that fit the 911/915/930 differential (and vice versa).
The BIG problem is that they fit, just not correctly.
There are even more significant differences if we are using ZF LSD flanges.
I used to have all these measurements.
I’ll see if I can find them.

The ’69 transmissions have the ball-pivot for the clutch arm positioned for the 215 mm push-type clutch.
No issue there when you use the 1969 and earlier 215 mm clutch.
The only issue here is there is not the oblong boss for the clutch arm pivot pin, allowing a ’69 901/xx to be converted to pull-type clutch without welding on the main casting.
Converting a 911/xx from 225 mm, pull-type clutch to 215 mm push-type ‘only’ requires machining and a threaded insert.
I have several 911/xx with ability to have either pivot.

The ’69 transmissions will also have the proper retaining ring for the push-type Bowden tube.
You will need this Bowden tube and a ’69 clutch cable.

Something to consider; in ’69, the clutch lever arm at the pedal assembly was longer than in ’70-’71.
If you maintain this ’70 part, you will have less force and longer throw than if you use the ’69 part.
The other way around is to always use the longer arm, allowing faster operation of the clutch.

The clutch release (TO) bearing guide tube is longer on the ’70-’71 type 911 than on all the earlier type 901.

The best push-type link between the cable and arm (“plastic piece”) is a steel ‘wedge’ type.
Carefully make clearance between the arm and the link at the corners of the ‘slot’ in the arm.

You will have no problem with your 2.2 engine oil hose that goes over the transmission.
Problems arise when you use the early ‘under-the-transmission’ hose-pipe assembly with the 2.2 pull-type clutch linkage.

The aluminum case 901/xx transmissions do not use spacers between the nose casting and the transmission mount.
The magnesium case 901/xx uses unique-to-‘69 spacers.

The mag case 901/xx have an issue with cracks in the main casting.
These are above and outboard of the input shaft roller bearing.
They appear to be related to the steel insert bearing retainer.
There is commonly some minor oil leakage.
I have never seen this cause a mechanical issue.

Other things like back-up light switch and shift linkage aren’t an issue.



For reference, the transmissions involved here are:
For 1969.
901/04/06 alu 4-speed.
901/05/07 alu 5-speed.
902/14/16 alu 4/5-speed.
902/50/60 alu 5-speed specials.
901/75/76/77/78/79 alu 5-speed specials.
and
901/12 mag 4-speed.
901/13 mag 5-speed
901/16 mag 6:29 912 5-speed.
901/80/81/82/83/84 mag 5-speed specials

Compared to the ‘70-’71 transmissions:
911/00 mag 4-speed.
911/01 mag 5-speed.
911/80/81/82/83/84 mag 5-speed specials.

There are more.

If someone finds an error or extension with this explanation, please post.
Accuracy is critical and I'm no longer perfect (as I'm no longer a teenager).

Best,
Grady

[classic]

Grady,

You're such an asset to this community/forum