Posi traction

[Green69]

Gents,
I have two questions for you.

One: To confirm that you CAN fit a 3.73 ring and pinion onto a positraction previously fitted wit a 3.55.

Two: Can someone give me a measurement.

I need the distance where the arrow is from a 3.55 diff carrier.

Here is another picture showing the difference between two posi carriers. Series 3 and 4


Many thanks in advance.
Thierry

[Vettech]

You guys seem to know all this good stuff, so can i ask a few stupid questions, I always understood that Positraction or LSD diffs had those "springy thingo's" like the one in your pic. The positraction was an option available on all diff ratios !  So can I assume that they used the same basic diff and put extra bits in or stronger bits like in your pic ? I can see that the base model 68/69 was either a three speed manual 327 (68) or 350 (69) driving a 3.36:1 diff. But there was three optional 4speed manuals and an M40 TH Auto box driven by a host of 350, 327 and 427 engine options. (No 454's !?!?). One can only wonder how many diffs would then be optional. This is getting a bit tooo NCRSeeeee!

[sirfixalot]

I have a 3.55 carrier here that is a doorstop you can have to do all the measurements you like it is stuffed

[rosco]

Okay this what I know and Bfit will I hope correct me if I have it wrong.
All ratios to 3.90 came with a series 3 diff, 4.11 and lower were series 4.
3.73 is a after market gearing the Gm one is 3.70.
If your diff came with a 3.55 all good as long as you got a series 3 ratio to put in it.
Series 4 posit will not fit a series 3 rear you will need a series 4 carrier.
I will try and find a contact for you in the states and he will give you all the advise you need on rear ends.

Rosco

[bfit]

Series 3.  Up to 3.7:1
Series 4.    3.9:1 up
Bfit

[Green69]

All right,

Vettech, At one stage, 3 different gear carriers were available !! Today the after market choice of ratios are quite limited to compare!

Sirfixalot, I just need one measurement. Please could you check it for me ? It would be much appreciated

Rosco, Thank you. this confirmed what I knew. For the advices, I always appreciate them, I am currently dealing with TOM's in the US of A. And I try not to look like a goofy when talking to him !

Bfit, thanx as well, we are on the same page.

I am bothering you guys, because I am going a different way regarding the lsd by not fitting a Eaton Positraction.

[bfit]

I like the thought of going a different way,
I'm currently working on fitting a 9" in one of my vette's
The options are vast for a 9"
Bfit

[Green69]

Hehe! Let us know the progress of it. Definitely interested .

[rosco]

http://www.markwilliams.com/images/93012.jpg

This would be nice and its a 12 bolt but is $4750 US

Rosco

[Vettech]

No one commented on my question on the spring thingies, could they be preload springs that apply force to the clutch packs located in the diff. Is it true that the easy way to tell if you have Posi/LSD is to jack up rear, both wheels off ground, turn one and if v other turns in same direction you have LSD, if not its a std diff (wheel turns in opp direction). Are Eaton diffs called mechanical lock because they use a governor to lock the diff action. And here I was thinking diffs were simple creatures. Oh and my son said "dad why dont you check the diff tag if it has an 4L.11.xx then the "L" means "lsd", that's probably rubbish - what would he know!!!!!.....

[Green69]

Well!
You can have the spring thingies with different rates who apply their tension onto the disks, either steel or carbon fiber. And, you can have a Posi with no spring thingies ! A tuned Posi they call it, apparently better than the springy one. I never tried one so cannot say.
About checking the LSD, you are right in the way how to do it.
I would maybe call a mechanical lock , a Detroit locker for example, not a Limited Slip Differential who use friction, but that its just me.
You can check the stamping on your diff or if you are lucky, you still have that red tag attached to the filling plug who said to use lsd oil only.

Cheers.
Thierry

[sirfixalot]

So you want the dimension third up from bottom on your diagram?

[Green69]

Yes, I would like to confirm or not if the 118.25 is the same on yours. It can be close enough like 118mm, do not go overboard taking the measurement.
Thank you very much for your time.
Thierry

[sirfixalot]

Checked it out today still has the bearing on that side is 118 mm  as per the diagram.

[Green69]

Thank you very much Sir!