Ok, in the next few weeks I'm gunna have a crack at chopping down a Commodore Borg Warner (BTR Engineering) LSD diff to fit in my ute. An irrelevant bit of information but it will be a four link setup with Watts Link lateral movement control.

Apart from "Get the diff shop to do it" (boring) I'd love some advice from guys that have had a crack at it and failed or suceeded.

I've stripped the diff (and a large chunk of my finger with the angle grinder in the process!) so I'm ready to measure it all up and chop it down to suit.

The plan is to make and use an aligning jig that I've seen on a few modification forums to get it all square to the diff centre. It's basically a steel rod that runs through a set of dummys that go into the where the carrier bearings sit and then there are more dummys that go into the end of the axle tubes to line the ends up prior to welding.

Love to hear any other methods of making it all square. And photos of the process if you have any.

Cheers!

I'm not sure but I have a whole r31 LSD rear end here, minus LSD and gears if you'd rather use that so you can have 4 x 114 stud pattern - or convert it for me lol

I had a Race shop do my first one and they did a terrible job all square, but saddle mounts were terrible, the caliper position was all wrong ( even though I had specified where I wanted it) so I am doing the next one myself. I used a HD tube cutter to cut the tubes down and then I machinched up some sleeves that were a press fit and welded into place this way I could rotate the caliper position so the handbrake should work a lot better.

First cab off the rank - run the steel bar and collars through the unshortened diff (if the bar is long enough to do so) and check to see if it is square to start with. It's not uncommon to find 1-2 degrees of angularity (well 2 would be rare, 1 isn't) in the existing axle tubes. If this is the case, you should consider heating and straightening it (often just heating it on one side then letting it cool can alter it back)

In stuff like ford 9" diffs where the whole housing is sometimes re-inforced with extra RHS steel, you have to straighten them a few times during the process.

Beyond that, take your time. measure twice cut once, sort of thing. And don't be in a rush to weld the tube ends back on, short bursts then allowing it to cool will tend to avoid distortion.

Some places 'cheat' and use the short axles from one side of a diff to be the new 'long one' on the shortened diff (sometimes the measurements just happen to work out like that, and it's one less axle to re-spline.

If at all possible, try and avoid that, because if an axle has been 'stressed' in one direction all its life, it won't tend to last long if put in 'reverse'

There was a thread on performance forums about a bloke going it all by himself from scratch, and the results were good, I'll try and dig up some pics if you like (though there was a server crash a few years back and a lot of stuff was lost)

Another thing I'd maybe suggest - is that in general, being a very light car, you can get away with the 25 spline version of these diffs for most apps in a 1200 (even probably an sr20det, for anything short of massive high hp drag racing with super sticky tyres). Which means the housings might be able to be had cheaper from earlier model cars vs (for example) the 28 spline vl turbo spec one, which tends to fetch a bit of money

People have gotten into the 12s and below with one of the 25 spline units in valiant chargers (the aussie ones) - which probably weigh over 1.5 times what a full bore 1200 would.

Thanks guys, that's some good info.
John- my diff is out of a VS Commodore so it's a 28 spline anyway (it was only $250!). I'd imagine I'll be busting trannies before axles (unfortunately!). The Borgies can cop some serious punishment.
If you did track down some photos/links that would be great.