41 replies to this topic

[hanra]

Can anyone say with certainty that a 2.78 crown wheel & pinion would fit onto a LSD fine spline hemisphere that currently has a 3.55 mounted to it?

That 3.55 centre is fitted to a housing which has all studs except two long bolts at the 6 & 7 o’clock positions.

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Edited by hanra, 25 October 2023 - 05:38 PM.

[hanra]

This is the 3.55

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Edited by hanra, 25 October 2023 - 05:48 PM.

[S pack]

The crown wheel mounting flange on the 2.78/3.08 case is said to have a different offset to that of the 3.55/3.36 case. That is why the same part has different part numbers for the different ratio applications.

Who knows what the diff mob have done with yours Brad. Prob best to go back to them or another diff rebuilder to get their opinion on what can and can't be done.

[yel327]

Is it a long bolt carrier? If it is and I’m understanding what you’ve said, you have a 3.36-3.90 LSD centre in a 2.78/3.08 carrier?

[hanra]

The centre is a 3.55. The entire carrier assy (section that bolts to the housing) is the same one that was used for the 3.08 that came with the car when I bought it.

It has 2 cast sections at the 6 & 7 o’clock position where the two long bolts go through.

The crown wheel mounting flange on the 2.78/3.08 case is said to have a different offset to that of the 3.55/3.36 case. That is why the same part has different part numbers for the different ratio applications.
Who knows what the diff mob have done with yours Brad. Prob best to go back to them or another diff rebuilder to get their opinion on what can and can't be done.

When you say case, do you mean the LSD hemisphere?

Edited by hanra, 25 October 2023 - 06:53 PM.

[hanra]

I’m learning a lot from this thread. And will try and get my terminology correct.

https://www.gmh-tora...fferent-ratios/

Well after pulling some shit apart, here we are:


Limo and Gearex were spot on. Looks like about .060"-.070" difference

[claysummers]

The carrier, I’m calling it, if it is the same as your 3.08, will use a long stud at the bottom of the housing, and a long drain bolt. If not they are both 3.36 or shorter, which is unlikely but possible. Still, the 2.78 has such a large pinion gear, you may or may not need to provide clearance for it in depth. Sorry for all the ifs and buts…


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[hanra]

Ok so trying to use the correct terminology.

The LSD case I have was always fitted to a 3.55 crown wheel which was fitted to a carrier that didn’t have the provision for the long bolts. Looks like it used all studs? I bought it as a complete assy 2nd hand.

The diff shop took my long bolt carrier assy (which had a 3.08 fitted to it) and mounted the LSD case including the 3.55 crown wheel & pinion to it.

[S pack]

The carrier, I’m calling it, if it is the same as your 3.08, will use a long stud at the bottom of the housing, and a long drain bolt. If not they are both 3.36 or shorter, which is unlikely but possible. Still, the 2.78 has such a large pinion gear, you may or may not need to provide clearance for it in depth. Sorry for all the ifs and buts…


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That is correct Clay, the Carrier is the cast iron housing that all the diff parts are assembled into. I believe Brad's banjo diff has it's original 3.08 (two long bolt) carrier.

In the pic Brad posted Heath calls those parts Carriers but they are not, the are referred to as the Case. Well that is the terminology used in the GMH parts catalogues and workshop manuals.
 

Ok so trying to use the correct terminology.

The LSD case I have was always fitted to a 3.55 crown wheel which was fitted to a carrier that didn’t have the provision for the long bolts. Looks like it used all studs? I bought it as a complete assy 2nd hand.

The diff shop took my long bolt carrier assy (which had a 3.08 fitted to it) and mounted the LSD case including the 3.55 crown wheel & pinion to it.

3.55/3.36 Carrier has all studs except for the short drain bolt at the bottom (6 o'clock).
 

Edited by S pack, 25 October 2023 - 08:05 PM.

[hanra]

So basically I cannot use my LSD case to bolt the 2.78 crown wheel to.

Edit: Or perhaps I could looking at Heaths comparison pic. But the crown wheel would need to be shimmed accordingly.

Edited by hanra, 25 October 2023 - 08:09 PM.

[yel327]

You could sell the 3.55 gears and LSD unit and fit a Trutrac with the 2.78 gears.

[claysummers]

Have you torque tested the LSD centre and what sort of life has it had? Probably well worn by now.


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[S pack]

So basically I cannot use my LSD case to bolt the 2.78 crown wheel to.

Edit: Or perhaps I could looking at Heaths comparison pic. But the crown wheel would need to be shimmed accordingly.

I don't believe you could bolt a 3.08 or 2.78 crown wheel straight up to a 3.55/3.36/3.90 case. In Heath's pic it looks like the 3.55/3.36 flange would need material machined off to fit the 2.78 crown wheel.

It does look like a 3.55/3.36/3.90 crown wheel could be shimmed to fit onto a 3.08/2.78 carrier though.
 

Edited by S pack, 25 October 2023 - 08:52 PM.

[hanra]

I had the diff shop rebuild it all 12 years ago. It’s done 2500klm. Seems pretty tight as you can hear the inside tyre biting on the asphalt when you do a low speed turn.

I don't believe you could bolt a 3.08 or 2.78 crown wheel straight up to a 3.55/3.36/3.90 case. In Heath's pic it looks like the 3.55/3.36 flange would need material machined off to fit the 2.78 crown wheel.
It does look like a 3.55/3.36/3.90 crown wheel could be shimmed to fit onto a 3.08/2.78 carrier though.

Ahh perhaps I’m looking at the incorrect side for where the crown wheel mounts to.

You could sell the 3.55 gears and LSD unit and fit a Trutrac with the 2.78 gears.

I think that also requires new axles?

Edited by hanra, 25 October 2023 - 08:55 PM.

[hanra]

Looks like this Tru Trac would suit the stock fine spline axles?

Dosnt seem to show an option for the differing gear ratios however? So one size tru trac case fits all ratios??

https://www.harrop.c...banjo-23-spline

Edited by hanra, 25 October 2023 - 09:15 PM.

[claysummers]

Let’s hope you can use it. Fair jump in gearing.


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[yel327]

I had the diff shop rebuild it all 12 years ago. It’s done 2500klm. Seems pretty tight as you can hear the inside tyre biting on the asphalt when you do a low speed turn.

Ahh perhaps I’m looking at the incorrect side for where the crown wheel mounts to.

I think that also requires new axles?

 

That is how they used to do it aftermarket in the USA with GM 10 and 12 bolt diffs, but from memory it only works one way, the other metal needs to be removed.

 

I thought you could get Trutracs with the smaller spline counts.

[claysummers]

You can get 10 spline but don’t see the point. I know a bloke has one in his Eldred Norman supercharged grey motor EK ute.


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[hanra]

That is how they used to do it aftermarket in the USA with GM 10 and 12 bolt diffs, but from memory it only works one way, the other metal needs to be removed.

I thought you could get Trutracs with the smaller spline counts.

I’ll shoot harrop and email. They list a 23 spline option. Just wondered how it handled all gear ratios considering GMH uses two differing cases.

[S pack]

I’ll shoot harrop and email. They list a 23 spline option. Just wondered how it handled all gear ratios considering GMH uses two differing cases.

Perhaps they will need to know your gear set ratio at time of ordering?

[claysummers]

Jeez they’ve got dearer?


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[yel327]

You can get 10 spline but don’t see the point. I know a bloke has one in his Eldred Norman supercharged grey motor EK ute.


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The point would be if you were restoring an original HK-HG Brougham or V8 HT-HG GTS or even a 307 HK Premier or 307/308 HT-HG V8 Premier and needed to fit a 2.78 LSD or 3.08 LSD banjo to it. Original Borg Warner LSD centres for these are all gone. A coarse spline Trutrac is a cheap and ready to go alternative.

[claysummers]

Why wouldn’t you fit the fine spline spider gears and axles so suit, custom no doubt, if you’re spending $2k already though? In my mates case the early grey crash box is the weak component, but behind a stronger box the axles would be next weak point, followed by the crown wheel?


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[RallyRed]

Looks like this Tru Trac would suit the stock fine spline axles?

Dosnt seem to show an option for the differing gear ratios however? So one size tru trac case fits all ratios??

https://www.harrop.c...banjo-23-spline

Hi mate,  when I was buying a Harrop Tru track back in 2014?....there was never ANY discussion/question via Harrops, to find out what gears I was planning to use on it...thus, I assume ANY gers in the 3.55 -2.78 range will fit.

[RallyRed]

Also, in the shed, I have complete diffs of all ratios in factory configuration  - I expect course or fine is irrelevant in this discussion?

( except maybe 3.08 that has a D/locker fitted, would need to check.)

 

Are there any key measurements I could take to put it to bed for ypou?