Ba Falcon diffs

[alffie]

Has anyone ugraded or had problems with the BA XR8 diffs

[Beejay]

Alffie,

The guys here are putting down some good track times with the standard AU diff.

If you were thinking of changing this to something stronger I would imagine there are better options than the BA unit. You could probably get some dish on the rear wheels too.

Ben

[alffie]

To late now to change the rear set up my rims are already here. I wanted to see if anyone had a 9 inch center conversion like you can with the commodore rear end. Iam a bit worried the LS7 will distroy the center.

[Philm]

Hi Alffie,
You have uncovered the achiles heal with the CR.

The BA or AU rear struggle to cope with the power we are putting thru them. Ratrace has broken his along with CV joints with a power launch at the drag strip.

We have no real options hear as a 9 inch is physically to big to fit in the space we have.

With 470RWHP and 650plus with N02 , it will break for sure. The only solution is to drive the car to look after the diff, no hard launches, get it rolling then nail it.

If anyone has a solution for this i would live to hear.

Phil

[alffie]

Ive been told you can fit the hydratrak out of the commodore. But that wont solve the cv issue. The LS7 has 484 RWHP so looks like I will have to come up with something. Although with 650hp in a cobra it would runs 10s easy and with that comes the cost of safety gear that ANDRA make you have. Steady launchs will save my clutch to I guess.

[alffie]

How long does the LSD last?

[Philm]

Alffie
The LSD is not the problem , the Hydratrack is still an 8inch crown wheel. Mike has fitted one of these to his car and while better still a bit away from a traditional 9 inch.

We have a fully aprooved ANDRA cage installed in our car and all nessesary Andra equipment, licences etc.

Hoping to run a 10.99 without the gas.

Have run a 11.7 at 120MPH, with a very slow 60 foot time, we have a new clutch and 3.9 gears in the car now so looking forward to the next drag day.

Phil

[Aussie Mike]

Hi Alffie,

I'm the one that did the Commodore diff conversion. Who mentioned it to you?

The AU ford diff is a BTR-75 center which has a 7.5" crown wheel. At the time when I was building my rear end there were only 2 ratios available for it. 3.23:1 and 3.54:1 I wanted 3.7:1 or 3.9:1 so I bought a BTR-80 center from a VU GTS Commodore. This center comes equipped with a stronger 8" crown wheel and 3.9:1 gears and a Hydratrak LSD center.

The BTR-75 and BTR-80 share tha same back cover bolt pattern. I used the Ford AU back cover on the Holden center so I retained the standard rear chassis mounts. I machined the back cover to add a fill bung as the Commodore housing has the fill plug in the back cover where the for has the fill plug in the housing. I also welded a tube through the rear cross member so I could get to the fill plug.



I cut and boxed the cross member in front of the diff as the front mounts on the diff housing hit on it. I then fabricated and welded in a new front moung to suit the Commodore housing.



I made up some nolathane front mounts for the diff but If I did it again I'd probably solid mount it as the extra vibration would probably go un noticed with side pipes and everything else going on.



I'm using the Commodore axles as well. I never liked the Ford axle design since to remove an axle was a major pain in the arse requiring stripping down most of the rear end. I can undo the 6 bolts one each end of the axle and drop it out almost without turning a bolt on the rear suspesion.

I also plan on fabricating some tubular molly upper and lower control arms that will be 2" narrower each side. The commodore axle setup makes life easy for shortening the rear with the way I've done the drive flanges at the wheel hubs (unfotunately I don't have any pictures of them).

The 6 ball CVs seem to be a bit stronger than the 3 roller style used by the Falcon (Going by the punishment the Commodore guys dish out). There are also aftermarket CVs available in this pattern that are much stronger. The standard Commodore axles are also 2mm larger in diameter than the Ford units.

Cheers

[sambo]

That is some serious effort and know-how on your behalf Mike - well done. If/when my Cobra's power outgrows the Skyline diff I might need one of these conversions too. In fact I think Harrison now offers a Commodore-based IRS, albeit at a price.

[Aussie Mike]

I think the Skyline has the same 8" crownwheel and pinion as the Commodore. I believe thats where some people have been sourcing 4.11:1 gears from.

It's not going to be as strong as a 9" set up but at the time a 9" IRS center was going to cost me more than $5K. I did the conversion more with getting the ratios I wanted in mind. I also liked the idea of the viscous coupled LSD with it's more progressive engagement.

I should also mention that the standard Ford axles will work with the commodore diff setup too as long as you use a regular LSD (Hydra trak has a special axle with an extra splined section on the end).

Cheers

[alffie]

Thanks for the pics Mike. Harrop make a alliminium 9 inch conversion for the Commodore rear end. Did you use the Commodore hubs or keep the Ford hubs?

[Aussie Mike]

I machined down the ends of the Ford axles and kept the spline where it plugs into the Ford hub. I then machines a drive flange for the Commodore axle and welded it to the flange I had machined on the end of the Ford splined section. I welded it all in the lathe to keep it concentric true much like the way they weld drive shafts together.

Unfortunately the Harrop 9" center section wont fit without major mods to the rear cross member.

Cheers

[Aussie Mike]

The Harrop 9"center section is also about $7500 and you still need to buy a set of gears and an LSD for it. I reckon it's close to $10K for that setup.

I could probably drop the harrop axle setup into my rear end setup without too much work.



Cheers

[alffie]

Geez I hope my rear end holds up, thats a lot of work, I wish I had of looked into the Ford rear end a bit more before I got Chassis with the BA rear.
The problem with the BA rear is know one is racing the Falcon so there is no demand for upgrades like there is for the Commodore.
Ian told me one of his customers had gone to the Commodore rear.

[alffie]

What about the Kratzman diffs? Theres a guy in Melbourne with a VP that has one. Harrop are way over priced, always have been. I think there is another mob that do a 9 inch conversion.

[Aussie Mike]

Did Ian build your chassis to suit the BA diff rather than the AU diff? Id like to se a pic of that if you've got one handy. I hear the BA falcon went way from the BTR center and are using a DANA rear end. My wifes friends hubby works for DANA on the supply of suspension and differential components to Ford for the Falcon and Territory.

I believe the BA center is significantly stronger than the AU center but I'll have to do a bit of research to make sure.

The thing to remember with these cars is that they weigh nearly 700KG less than a Falcon or Commodore. That adds up to a lot less strain on the diff which means we can safely throw more HP at it. I think a 9" is probably overkill for what we are doing.

Cheers

[Philm]

I am not real sure but the center in my diff is from a comodore, not the Hydra like Mike and has 3.9 gears which are from a skyline, probably the strongest you are going to get.

I think we are ok but you have to treat them with a little respect.

[400TT]

I'm really not sure how strong the Skyline rear-ends are but we've had some big HP Cobras giving them years of abuse at Drags, Sprints etc. No breakages yet, amazing.

It's the same story as those Porsche G50 transaxles in the DRB GT40's. A lot of serious power gets put through them and they cop a lot of abuse from drags, sprints etc. Peter Ransom has also had a few of the GT40's doing burnouts for display at a few race meets up here.

[alffie]

It has Ford and BTR all over it so it isnt a Danna. Ian refused to put a Commodore center in my kit.

[Tenrocca]

There was a car at nationals (Mark from Grenfell), with a 545? BB - he has the AU rear end, shortened axles and a jag centre. Not sure if he has driven it in anger yet though.

(oi Mizzi - nice signature )