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Diff centre help


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#1 Gatti

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Posted 27 January 2020 - 02:20 PM

Hi,

Can anyone confirm which diff centre I have in my LJ.

I’m pretty sure it’s 3.08 as it revs at around 2700rpm at 100k’s

Is it coarse or fine spline?

I thinking of changing it to 3.36 or maybe 3.55

Here’s a pic of the numbers on the Vicente.

76550e3f8b62b8f9a22b75b5a2d3b52f.jpg



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#2 yel327

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Posted 27 January 2020 - 02:28 PM

Haven't looked at a banjo for a long time but that doesn't look like a 2.78 or 3.08. I'd say you already have a 3.36 or 3.55. You can't tell if its fine or coarse spline from that picture, have to pull an axle out. That code is the date the centre was cast.



#3 S pack

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Posted 27 January 2020 - 03:12 PM

Take a pic of the underside of the diff. The ratio should be stamped into the face of metal flange on the yoke.


Edited by S pack, 27 January 2020 - 03:13 PM.


#4 gtrboyy

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Posted 27 January 2020 - 04:12 PM

Flat plate under diff yoke should syill have ratio stamp on it....vaguely remember dudes could get rough idea of ratio looking at the 2 bottom bolts whether they're short or long.

 

Majority of diffs were coarse spline but easiest way is pop axle out.



#5 claysummers

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Posted 27 January 2020 - 04:49 PM

Odds on it’s a 3.36 coarse


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#6 S pack

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Posted 27 January 2020 - 04:53 PM

Being a Torana S XU1 tribute it will likely be a 3.08 course spline open centre but as it is not the original banjo for the car then anybody's guess really



#7 Ice

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Posted 27 January 2020 - 04:53 PM

Odds on it’s a 3.36 coarse
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At that rpm i agree

#8 Gatti

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Posted 27 January 2020 - 07:13 PM

I read the rpm versus ratio would be like below at 100 km/h?

3.08 would be 2700rpm

3.36 would be 3100rpm

3.55 would be 3300rpm

I’ll have to Jack the car up to have a look at the stamp on the diff as it’s too low to get under


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Edited by Gatti, 27 January 2020 - 07:15 PM.


#9 S pack

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Posted 27 January 2020 - 08:51 PM

I read the rpm versus ratio would be like below at 100 km/h?

3.08 would be 2700rpm

3.36 would be 3100rpm

3.55 would be 3300rpm

I’ll have to Jack the car up to have a look at the stamp on the diff as it’s too low to get under


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Perhaps you need Jenny Craig :D



#10 Gatti

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Posted 27 January 2020 - 09:07 PM

Perhaps you need Jenny Craig :D





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#11 Gatti

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Posted 06 February 2020 - 10:07 AM

I swapped out the diff centre last night and it was a 3.08

 

I've learnt a bit about them now and hadn't realised that 2.78 and 3.08 have the 'long bolt' case and 3.36 and 3.55 are 'short bolt' which is easy to identify.

 

I took the car for a quick run around the block last night and it feels good with the 3.55's, but I just need to wait for the rain to stop so I can take it for a long run 



#12 yel327

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Posted 06 February 2020 - 10:15 AM

The 2.78/3.08 were originally built by Borg Warner for GMH and the cases were nodular iron intended for V8 use, whereas the 3.36 up were normal grey iron made by GMH. I think GMH started building the 2.78 and 3.08 once they started being more widely used in HT with 253. At a similar time they were made optional with LSD, prior to that I’ve never heard of one that wasn’t LSD. Not sure if they reverted to grey cast iron once GMH started making them.




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