How To: Simplified Differential Upgrade

[randywebb]

Certain older 911s up until and including 1971 (see: Simplified Differential!)
have a Simplified Differential which can destroy the transmission -- "saw it in half" as Grady put it.

There have been several previous threads on this issue, but no one has posted a detailed "how to." Scott Clarke fixed his 1971 tranny recently and was gracious enough to let me take pics.

You should begin with a deep mediation on the nature of things mechanical. Here, Scott is really trying to figure out how to set the backlash, but I couldn't resist including the shot here (you will not need to set the backlash for replacement of the bolts, etc. here).






The top bolts are the ones used in the simpl. diff. setup. If you pull these out of the drive flanges, then you have a simpl. diff. and are at risk.

They will be replaced with the other bolt (the one w/o a nipple on the end) and the pin will replace the job of the 2 bolt nipples. You will also need to order up the armature in a post below. Total cost is < $75.

Diff. Armature 911-332-208-00
Hex Screw 901-332-275-12
'Cotter' Pin 900-308-005-00
drive flange bolt 901-332-275-12 (need 2 of these)

[randywebb]

My understanding is that you can do this with the trans. in situ tho it will be easier to do it with the trans. out of the car and on a nice, clean bench. Grady has pointed out how damaging even a single grain of sand can be, so...


Here is what things look like with the side cover removed...





then just pull the diff. out...




I included this shot so somebody could explain what those two green bands are for?? They must ID something...

[randywebb]

Open up the diff. by driving that shaft out. The armature is going to fit in between those two small gears (you can see the bottom one in situ in this pic).




Here is a close up of the bolt nipple. Maybe Grady can post and say if that is a lot of wear we are looking at, or if the nipple is machined at the factory. Anyway, you can keep these 2 bolts as a curiousity, but you don't want them in your tranny.


As an aside - note the dirt particles revealed in this macro photo... when you clean something that is precise, you need to really clean it carefully - your naked eye would not see these particles.

[randywebb]

The armature will wind up sitting like this in between the two small gears in the diff.


Note the cutaway part of the armature - that allows you to push it in while you hold the gears in place with your other hand.






Like this:

[randywebb]

Once the large shaft is driven in...

and aligned, you can use a pair of needle-nose pliers to hold the pin in the correct place while you drive it down with a hammer.

Note the "R" stamped into the end of the shaft -- maybe it has a particular orientation (?) Might be smart to keep track of which end is which when you remove it.




The assembly will look like this. Be sure everything is nice & clean.




Replace the diff. in the case, and button it back up, being careful to to observe the proper torque on the nuts and sequence of tightening.

Use new Schnorr Washers on the CV joints, and do all the other stuff to properly reinstall them (see Randy Cale's thread, recale). This is a good time to service the CV joints also. You can clean the exterior of the case and protect it with Tectyl, or perhaps some of the other products that were discussed in other threads -- some good person will search up that thread URL and post it here...


{Grady, Scott, others -- what did I forget??}

[brendon]

That's fantastic!! I am tempted to tear into my tranny now, even though it doen's 'need' anything.

[Scott Clarke]

I'd just add to make sure to order a new o-ring for the side cover also. The flat washers used behind the nuts retaining the side cover are special items, and are still available from Porsche. It is good to replace them. The nuts are special, too, but NLA. Also, be sure to check the other threads concerning this subject.

This project is really quite manageable, and can save you from a complete disaster. It should be included in Wayne's "101 More Projects," if that is still a going concern.

God work, Randy!
-Scott

[randywebb]

Thx Scott.

If you don't believe the phrase "complete disaster" is accurate, here are a couple of threads:

Unknown transmission

http://forums.pelicanparts.com/porsche-911-technical-forum/249100-901-let-go-bang.html#post2574356

Take a look at his input shaft, and also note Grady's comment "saw the transmission in half."

Scott had noted that the washers he mentions above are designed to go in between Mg and Al. He hasn't sent me the p/n's but they are still available. The nuts are NLA.

Also, I could not find the O-ring at Pelican by itself. I've used US sized O-rings in a pinch - O-rings stretch so it should work ok if the size differential is not too great. Scott tells me the correct, metric sized O-ring comes with the trans rebuild gasket kit.

[randywebb]

I've updated some of the posts above to include the part numbers.

Also, if you can't find these parts at Pelican or a local dealer, you can get them at Stoddard's.

[Eljimberino]

Hello

Has anyone done this upgrade recently?

Cogcogs seem to have the parts but they need modifications.

Is that correct?

The guide above implies no modifications.

Anyone point me to where to get the right parts please?

Thanks

[oldie44]

You cannot do this conversion on a 1966-69 aluminum case transmission. The differential housing is too small to accept the later parts.
Porsche changed the transmissions from al case to mag during the 1969 model year. I rebuilt a late 1969 and found that the differential housing was different than the 1970-71 housings and would not accept the later parts. I took some comparison pictures and posted them on a thread here years ago.
The 1970-71 transmissions should already have the late set up but I did open up a very early 1970 though that still had the early parts.
From 1966-70, Porsche used three different methods of securing the differential gears and 6 or 8 different axle flanges. Some parts can be interchanged; some not.

[Eljimberino]

Yes okay - as mine is a 1969 912 I would assume it's alu case.

901 301 301 2R is what's on my case.

So the conclusion is to insert new bolts with the nipples and change them over every 20,000kms?

[oldie44]

The mag case was introduced in the 911 in the middle of the 1969 model year. Way back when, I had a 1969 911S that had an aluminum case trans but late cases are mag.
I rebuilt a 1969 mag case transmission a couple of years ago and wanted to convert to the late diff gear retainers. Thats when I found that the parts would not fit.
If I were you, I would remove the bolts, inspect for wear on the nipples and replace as necessary. You can do the work with the trans in the car but only remove one bolt at a time to insure the hole in the cross shaft stays aligned.
My experience is they should last well over 50K miles before requiring replacement. There are tech articles on the subject in the PCA "UPfixing the Porsche". I think you can find them online.

[oldie44]

The al and mag cases are shaped different so just take a look to see what you have.
Also, there is only one version of the bolt with nipple. They were NLA for awhile but I think you can buy them again. If you cannot find them, I have some used ones that are in perfect condition.
I have taken some out where the nipple was worn down to half of its original diameter but did not fail. A little bit of wear os OK.

[JimmyT]

FS: '68-'70 911 Differential Bolt, Elastic, Simplified, Tool Steel, DLC, $31.52

[Eljimberino]

Check your private messages please.

Originally Posted by oldie44

The al and mag cases are shaped different so just take a look to see what you have.
Also, there is only one version of the bolt with nipple. They were NLA for awhile but I think you can buy them again. If you cannot find them, I have some used ones that are in perfect condition.
I have taken some out where the nipple was worn down to half of its original diameter but did not fail. A little bit of wear os OK.