Simplified Differential!

[Grady Clay]

Jim,

There is a threaded piece that fits there. We used to order them in quantity. I’m pretty sure the part number is in the P+A update flyer from ’71-‘72. We did hundreds of these in early-mid ‘70s. I had a collection of a dozen or so stretch bolts with tits in sequential stages of wear from new to failure – and an unbelievably destroyed transmission to show. We saved a lot of transmissions. Without this update (or at least regular replacement of the stretch bolts with tits) every one of these transmissions will eventually self-destruct.

What is the S/N of the 914 trans?

Does anyone have a late Type 911 or early 915 (mag case) apart and can provide some measurements?

With the correct donor pieces, I suspect you can machine a pair to properly fit. This isn’t tight clearances, just retaining pieces.

Best,
Grady

[Jim_Brown]

Hi Grady-

We exchanged a few emails on my transmission (my address is jester_jimmy@yahoo.com) before I decided to post here rather than just lurk. Let me know if you'd like the stretch bolts to add to your collection.

The 914 serial number is HA 6018998, model 914/11. I plan on fitting the donor pieces tonight.

Thanks,
Jim

[callook56]

I just took my ‘70T trans apart and found I’m the “lucky” owner of a simplified diff as well. I caught it in time thankfully but am now on the search for the updated armature and the 2 bolts. I have my local dealer looking into this but so far it doesn’t look good as far as parts availability goes. Does anyone have a source for the armature block and bolts other than searching for a 914 box to scavenge from?

[cameron.arnott]

In the same boat! Does anyone have a source for these parts or any kind of a work-around for this issue?

[callook56]

Contact Cogs cogs. He has all the parts you’ll need to do the upgrade. He helped me out and is super nice to deal with.
https://www.cogscogs.com/

[JimmyT]

FS: '68-'70 911 Differential Bolt, Elastic, For 901 Trans, $31.52

[kium]

Originally Posted by Jim_Brown

On the left in the picture below is the #5 threaded piece from the 901 differential with no extension to retain the armature. It looks like I'll need to have the 914 piece (on the right in the picture below) machined to remove about 4mm such that it matches dimension A on the 901 piece.

Looking at his picture it seems to me very easy to turn on a lathe the left piece to look like the one on the right, so it fits in the armature but with the correct height
Here is a simulation of how the piece would look like.



If this worked, it would make it much more easy than searching for parts changing all the spiders.
Any comments on this idea?

[kevingross]

Originally Posted by kium

Looking at his picture it seems to me very easy to turn on a lathe the left piece to look like the one on the right, so it fits in the armature but with the correct height

I'll be interested to hear how this turns out for you. A concern is that you may find the part is too hard (ie, steel had been hardened) to turn on a conventional lathe.

[kium]

mmm, could be it's hardened.
I should try to find another spare part and experiment with it first, or maybe give it a go, gently and see how it reacts...

[ClickClickBoom]

Originally Posted by kium

mmm, could be it's hardened.
I should try to find another spare part and experiment with it first, or maybe give it a go, gently and see how it reacts...

Surface grinder and rotary table. Should be close if the hardening is not surface.

[kium]

Hi guys,
a quick update on desimplifying my diff.

After taking your advice, I was quite afraid of turning the 901 threaded pieces and maybe loosing them due to the hardened steel maybe snaping and being left with no diff at all, so i wwnt online and was forunate enough to find a 914 diff for 30€ and with all the bits I wanted.




the 914 threaded pieces are way longer than the original ones, see here how high they sit over the armature withthe axle is in place.



So I took them to a lathe and removed 4.5mm of each piece.
BTW the lathe operator told me they were not hardened pieces and was effortless to remove the extra metal. Maybe because they are not really diff components, but somehow just nuts, they were no specially treated.
I asked the operator then to turn the original threaded pieces that came with the simplified diff into one of these later ones, just for the test, now I had the new ones I had no fear in breaking them, but refused because of the splines, they would break the tool, but could be done if needed. So sorry, I would have loved to show it done.
Anyways, here are the pieces after the turning



Here inside the 901 diff.



The original 901 axle slided in no problem, but I replaced it with the 914 axle because of center hole, it has to be 6mm for the roll pin to fit. The 901 seems to be around 5mm.
I also reused the original roll pin as it looked beefier than the new one I bought.

Dropped it the tranny, new o-ring (171x3.5mm) on the cover, but seems almost impossible to close.
I torqued down all the nuts carefully but couldn't get the lid to seat completly.
Removed the cover again and the o-ring looked squashed in some areas and round in others. It seems to slide out of the groove as you press the cover into the casing

Here's a pic with a new o-ring



To me it seems way too thick.
Do you guys know the corect way to close this cover?