So.... My Diff Is F***ed

[Kinkstaah]

Also, I don't know much (anything) about Diffs other than that they make wheels spin. Or in a bad case, wheel.

My diff makes a pretty hilarious high pitched whine at any speed (only on throttle) at 40kmh or higher. I have read a lot of diff whine threads here via search but mine is so loud that driving around at 8k RPM with a 5in exhaust and atmo bov would not come close to drowning out the sound, at least from perspective of the driver.

Going on that alone (correct if wrong) I assume this diff is most likely going to die shortly. Thus a new one is in order, as it was on the plans to upgrade "eventually". However I've found that there appears to be about a billion different options which seem rather confusing to the novice. In short, Kaaz or Nismo 1.5 ways do not appear to be a one size fits all item. I don't really even mind about brands, but couldn't find any info on compatibility anywhere other than for Nismo..

The car started life as an AUTO R34 N/A Series 2 Sedan. (long story, but the car is no longer N/A and definitely requires some sort of LSD, and it is still auto)

According to this chart -> http://www.nismo.co.jp/en/products/competition/lsd/pdf/lsdpro_price.pdf

The diff that is compatible is the 38420-RSS15-B5, with final ratio of 4.083

Is there anyone who can possibly confirm or deny this, or am I way off track? Wanted to be sure before ordering anything, as they cost a fair amount to find out that they don't fit/won't fit/can't be returned/can't be swapped/can't be made to fit and so on. I do realise that this is probably the most unlikely start car to ever go shopping to replace a diff in with a performance LSD - but figured if anyone would know it would be here.

[34GeeTeeTee]

Diagnose the problem first, could be as simple as a wheel bearing or pinion bearing that could save you $$$

If you WANT to upgrade the Nismo and Cusco are good

[GTSBoy]

Your first problem is that the noise is probably coming from the crownwheel and pinion. Any aftermarket diff that you buy is only the differential gearing pumpkin itself. You have to bolt a crownwheel onto it....usually the one from your old diff.

So you're going to need to consider getting some other diff first anyway. If I were you I'd just hang out for an R34 turbo diff in housing from a wreck and put that it. Consider buying a good mechanical centre for it later.

[Kinkstaah]

Is there any feasible way to determine what the problem is? I mean ultimately the 'want' to uprgade the diff is there, but my knowledge of everything is pretty shaky.

So step 1 is obtain a second hand diff that is not entirely destroyed to rule out the pinion/crownwheel? If that is then OK, that combo is used for an aftermarket diff center down the track then?

In the meantime, can I just use 'any' GTT diff?, Is there a list of things that are actually compatible? The current diff isn't a LSD of any kind, I wasn't aware if the turbo skylines of any kind came with a completely open diff from the factory.

[GTSBoy]

Take it to a mechanic, or preferably a diff specialist for diagnosis.

The manual GTTs had a 4.11 viscous LSD. The auto GTTs had (I think) a 4.08 viscous. There were supposed to be some manual GTTs with a helical centre the same as the S15 helical, but obviously with the 4.11 gearing. But I've not found anyone who actually has one.

Viscous LSDs are not really a proper LSD. They work for light power levels for a few 10s of thousands of kays and then they suck terribly.

Helicals are the ducks nuts for a street LSD unless your car is stupid low and you have to turn into funky driveways (in which case if you get a rear wheel off teh ground they go open and you get no drive at all).

And no R32 onwards turbo didn't have at least a viscous diff. The NAs were (mostly) open.

[Kinkstaah]

Yep that matches what I've read but thanks for the confirmation, I'll guess I'll have to check with a diff specialist in regards to what is actually compatible with other versions of the car (and potentially upgrading the middle down the track)

[donut_kng]

Having mucked around with a few of these in a 33 im assuming the shafts and tailshaft bolt (which I'd imagine they do) up - go for an auto turbo diff which would be a 4:3 ratio - easy enough to find in half decent condition out of a wrecked car. When your ready you can then do a centre as previously reccomended, trying to repair your diff will likely cost you more than buying a second hand one! Plus the noise is probably coming from outside the centre. Note if your car has Abs you'll have to find an Abs diff.

[89CAL]

Check your diff bushes as well. Mine has been much louder since I went polyurethene bushes everywhere around the diff, especially 60kmh or above. Might have a worn bush etc

As others have said check everything before just going out and buying a new diff

[Kinkstaah]

Thanks for the advice - Will post up here with results (if I remember) so anyone searching for a "what will actually fit my r34 gt" will actually get a result.

I imagine the upgraded center will have to fit whatever 2nd hand diff goes back in, at least I'll know whats going in so I know what to get

Thanks y'all!