Which diff for Hotrods these days

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Posts: 100
Joined: Thu Dec 22, 2005 10:20 am
Location: Brisbane

Which diff for Hotrods these days

Post by 34Chev »

Starting to think about a diff for my next project and it seems the good old days are gone
9” is still an option, can buy new housing to right length etc, expect to pay $2.5k then find a centre, might need a bank loan
Centura are rare, saw one recently for $875
Toyota Crown don’t exist anymore
2wd Hilux, maybe if you don’t mind 4.56 ratio
The latest word is Ford Explorer with a 2nd short axle. Can’t even find a one, let alone strip down a second one
Could go Jag again, but after spending a couple of grand reco on the last one, not as fun as it seems

So what is the modern hotrodder using?

Need to start looking at late model IRS, Commodore etc, width is always too wide, so will probably cost a fortune to shorten

Should have snapped up that $875 Centura diff, however that price just seems criminal, bought a couple in the old days for $100 each!

Anyone want to share their secrets?
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Location: Perth, WA

Re: Which diff for Hotrods these days

Post by thatold.chevy »

Chevy 6 stud - KZN165 (2003+) Hilux run a 3.7:1 LSD in the turbo diesel, and a 4.1:1 in the V6 petrol. Great ratio for taller 16x7.50 or so.

4.5in 5 stud -
Ford Explorer is the Falcon diff
ED - AU Falcon diffs are still good, range between a 2.92 single spinner and a 3.36 typically with an LSD. Better for street tyres around 28in.
Jeep Cherokee diffs are also fairly tough, and have a 3.73 ratio for petrol and a 3.07 for diesel too - but have a lot of garbage you have to cut off.

You also look at Commodore and 244 Volvo diffs, subject to PCD of course.

Cheapest and easiest way to shorten any modern diff is buy an extra short axle, and shorten the long axle tube to accommodate the short axle.

Makes for fun times when you start with a landcruiser / patrol diff for a fat tyre combo...!

First I checked the length difference between the long and short axle.

I just drilled out the plug welds for the axle tube through the housing,
removed the long tube,
shortened the end from inside the diff housing it by the measured distance,
reinserted the tube,
welded the plugs first then the tube to the housing.

Of course - you could do the opposite if you wanted to widen a diff, too - but you'd need a second long axle tube (or likely bare diff) too.

Was 99.999% straight and had no issues - measured the run-out to be less than 0.3mm. By shortening the inside, coil or leaf spring perches remain in the right place.

If your tailshaft is short you might have issues with the unis having too much angle, but in a bigger rod / valiant / early falcon etc there's no issue at all.

plus - what's a uni off ebay worth? $40? so you replace one every 10 years instead of every 20 - still a damn sight cheaper than a custom shortened diff.
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