Fine spline diff for FC

[Tortoise]

Hi guys,

I was wondering if anybody can assist me with some knowledge about fitting a fine spline diff into an FC?

I own an FC with a red motor in it and an HR rear end & course spline diff.  I want to run a fine spline diff and axles.  Is there any easy method fitting a fine spline rear end?  Does any other Holden have fine spline axles the same length axles as an HR or FC?

I know that some LH, LX & UC Torana rear axle housings had fine spline diffs, but I have heard the housings are wider than an FC or HR by about 6cm.  Does anyone know if this is the correct difference in width?   Is there any other Holden rear end that uses fine spline axles that is the same as, or narrower than the HR/FC housing?  Does anyone know how wide an LC or LJ rear end is?  Do LC or LJ rear ends have fine spline axles?

Tortoise.

[EffCee]

Tortoise,

A common swap is to fit LC-LJ Torana housings under FC's as the torana housings are about 25mm narrower, (Cant remember if it was 25mm per side or 25mm overall) allowing for a deeper dish wheel to be fitted. LJ GTR XU1 were all fine spline and were limited slip diffs. They are available, might cost a penny of two to get hold of a pair.

Simply cut off the existing mounts and weld on spring saddles, bolt it up and away you go!

Keith

[CraigA]

LJ GTR XU1 were all fine spline and were limited slip diffs

The LC/LJ all had coarse spline except the 150 '73 Bathurst LJ XU1's which had fine spline.

They are available, might cost a penny of two to get hold of a pair.

Spot on. With not many more than 150 sets ever made the price for a good second hand set (if you can find them) will be well over $1000.00.

I have a 260+ HP Red motor in my XU1 and use either 3.55 or 3.08 coarse spline LSD's. No issues with broken axles EXCEPT when I fitted a 3.55 CIG locker. Lasted one pass at the drags  

If you are looking for outright strength and aren't concerned about originality then why not fit a B/W diff? Lots of ratios and stronger than any banjo.

[fb delivery]

DON'T TELL ANYBODY
butt HZ used fine spline bang go's
 
  Rob

[FCRB26]

13 bang goes later i fitted a centura running commodore brakes.

[Tortoise]

Thanks for the posts. 

Craig A, your Torana sounds like a pretty wild ride.  I didn't realise course spline axles would handle that sort of power.  I have been told the Borg Warner rear ends handle plenty of punishment, but as you indicated, you like to change between 3.55 and 3.08 - that's not something you can do with a B/W, well not without pulling the whole rear end out, or setting up a new diff with the rear end still in the car.

EffCee, thanks for the info on the length of the LJ rear ends.  You mention cutting off the existing mounts and welding on FC mounts - will this cause distortion?  Would I have to get the housing set up on a jig to align it back straight? 

fb delivery mentions that all HZs have fine spline rear ends.  Even though HZs are way too wide, it got me thinking about how much it would cost to get one cut down, FC mounts added, and axles shortened and re-splined.  The other benefits would be that they come with tapered bearings, and HZ brakes.  I don't know if HR brake backing plates are interchangeable with the HZ housing ends, or whether I would have to use HQ to HZ brakes after that.

fchoon, you mention a Centura rear end - are they a B/W?  Or are they completely different?  Are they a lift-out centre?  How wide are they compared to a standard FC rear end?  What ratios are available?

Tortoise.

[EffCee]

Tortoise,

To cut off the mounts on LC LJ Torana diff, you would use an angle grinder, or an oxy. the housing would get hot, but not enough to cause distortion. When welding  mounts back on, use new mounts preferably, either self fabricated or Pete (fchoon) on the forum that can fabricate them for you. When  welding the mounts to the diff housing, use short welds that are diagonally opposed. Once the barckets are tacked in place to ensure that the location is correct, weld approximately 25mm then move to the other end and do the same. If you are welding with the front of the diff housing facing you, you would weld the front outer LHS first, the the RHS outer next, then the rear of the opposite side of the LHS then the opposite side of the RHS. You would then weld the other side front of the LHS and so on until you had all the brackets fully welded on. This minimises heat buildup and prevents distortion.

Have read through Pedro's build of his FCRB30 he does the same to a commodore diff. Page 30 I have included the link below:

http://fefcholden.org.au/forum/index.php/topic,13258.580.html

The Centura Diff are the same width as HR, and are a Borg Warner diff, which are slightly wider than that of an FC. Replace the centura backing plates with those from an XA-B-C Falcon (IIRC) and this will reduce the width further to that of an FC. You will need to have the Falcon axles resplined though to allow them to travel inwards enough.

Keith

[EffCee]

fb delivery mentions that all HZs have fine spline rear ends.  Even though HZs are way too wide, it got me thinking about how much it would cost to get one cut down, FC mounts added, and axles shortened and re-splined.  The other benefits would be that they come with tapered bearings, and HZ brakes.  I don't know if HR brake backing plates are interchangeable with the HZ housing ends, or whether I would have to use HQ to HZ brakes after that.

Sorry Tortoise I missed the above. To fit a HZ fine spline centre you would use a HR housing, this has the same brakes as the HK-T-G. This will give you a 10" drum and you can run 14" wheels. IIRC you can opt to use the HQ Drums with the same backing plates and have the axles plined to suit the fine spline diff. You could even elect to get an axle custom made if you want, the weakest point is always going to be the centre.

If you were to go to the HQ type pattern, you could always fit stubs from any HK-WB, they are all the same. Calipers interchange, tracks are altered slightly with ventilated discs from HQ onwards. Wheel bearings are the ame all the way through. Don't fall into the trap of trying to fit commodore rotors with HQ-WB calipers. The commodore rotors have less minimum thickness on the rotor, which will cause the HQ-WB caliper to possibly pop out as the pads wear down.

Keith

[FCRB26]

I ran centura with original drums redrilled
  originally with 13x7 ROH rims
before i went to commdore brakes on my centura diff.
 they are B/W 28 spline 2.92 auto and 3.23 manual but any B/W gears fit other than 2.78 which dont fit.

[FC427]

I ran centura with original drums redrilled
  originally with 13x7 ROH rims
before i went to commdore brakes on my centura diff.
 they are B/W 28 spline 2.92 auto and 3.23 manual but any B/W gears fit other than 2.78 which dont fit.

Hoon weren't Centura  25 spline from factory  I know that they can be changed to 28 spline ....FC427.....

[FCRB26]

Your probably right i might have drunk that brain cell away.

28 rang a bell thats all???

[Tortoise]

Thanks everyone for your help. 

I spoke to a diff modifier recently and he told me that once you get an axle re-splined, the result is not as strong as an orginal Holden fine spline axle because you've cut away the hardening treatment on the factory splined end.  He said that very few modifiers will give the ends a hardening treatment as good as the factory treatment.  He suggested that re-splining defeats the purpose of swapping to fine-spline axles, because a factory course-spline axle will generally be stronger than a re-splined fine spline axle anyway.

A shortened 9" would be nice, but the strength is probably overkill, and I don't really want the weight.

So its back to the drawing board for a bit more thinking.  Maybe after what Craig A said, I'll just stick with the diff I've got.

 

[FCRB26]

Brand new billet axles $230 each  solid as a rock with a borg warner no soft ends...

[2door350]

yes, centura are 25 spline, plenty strong, kept busting axles in my bango fc housing, after 6 or 7 broke i changed to the BW 2.92 and have never had a problem since...It has survived 4 engines, 3 gearboxes and two cars so far without one problem, recently updated centre to a 3.23 4 pinion LSD for some extra traction...

money very well spent i think....

[FCRB26]

And some chryslers came with 3.70s which arent that common but a good ratio