Today I had a chance to investigate and upgrade the simplified differential in my 70 911. I found the threads created by people who had done this before extremely helpful so at the risk of repetition I'm going to post some pictures I took of the process. Grady's information and Randy/Scott's account were particularly helpful, as was the article in Upfixin vol 4 (co-written by Grady). Project911's experience provided the motivation.
I wasn't smart enough to do this during the several months that my transmission was out while the car was being painted, but I was smart enough to eventually buy the parts and wait for an opportunity to dig in.
This weekend I was able to get my project 911 back on the road for the first time since July of '05. I drove it to and from the Pomona swap meet this morning, and have put a total of about 75 miles on the car since saturday. When I got back and started poking around underneath I noticed that 3 of the 4 CV boots (which I decided to reuse since they looked good) were weeping grease and one of them was spraying the wheel well. Needless to say, lesson learned. After cleaning up the mess I took off the axle shafts to replace the boots and repack the joints(again). I couldn't help noticing that the differential cover was quite exposed and some wheels in my head started turning.
The general opinion seems to be that removing the trans from the car is preferable to keep the inside of the transmission from being contaminated. My car is still pretty clean underneath so I decided to take the chance and go for it.
After draining I used an old steel stake to help me remove the old expansion screws. Once the bolts came out it was clear that my diff had never been retrofitted.
The differential cover came right off, and weighs practically nothing. Magnesium is neat.
Diff pulled, with the axles out of the way it comes right out with plenty of room. Really Really Easy.
The bolts exhibit a similar amount of wear as those seen in randywebb's thread. This is not a comforting wear pattern, and I'm sure glad that they're coming out before rather than after a failure. The main thing that caught my eye was the color - These bolts are gold and unlike any other color pictures I've seen. Perhaps they were replaced at some point? The car only has ~75k miles so it isn't super high mileage.
New and old hardware side by side
What the still-simplified diff looks like without the old bolts
The center spider gear shaft simply pushed out with firm finger pressure...I'd hate to see what would have happened if the bolts had let go.
Armature Added
A roll pin completes the upgrade
Finally it all goes back in with a new O-Ring. Putting it back in was as easy as taking it apart.
The parts I used were:
999-701-286-40 Rubber O-Ring
2x 901-332-275-12 Hex Screw 10x75
911-332-208-00 Diff Armature
900-308-005-00 Cotter Pin
Obviously, some gear lube was required.
I highly recommend that anyone who suspects they have this kind of differential check it out and perform the upgrade if necessary, it is child's play compared to most other mechanical operations we perform on a regular basis.