What to look for when buying diff

[turbodragon]

Hey,

Finally biting the bullet and looking to purchase a manual 3.45 diff for my Auto SSV (standard 2.92).

Just want to know, when I'm looking to buy, what are the things I need to be looking for and what sort of questions do I need to ask to make sure I'm not buying a lemon? Is there any way of seeing if a diff is really a 3.45 without cracking it open?

I know there are build plates on them but will taking a 3.45 build plate and sticking it on a 2.92 (or 3.27) diff be easy to spot as a dodgy diff?

Last thing I want to do is buy a 2.92 diff, thinking it's a 3.45.


Cheers.

 

[VE_CalaisV8]

I'm assuming you want to buy second hand off ebay or gumtree? Buy off a reputable seller who knows what they are on about. I looked at a 3.45 diff for my car and found one on eBay and the guy selling it was a wrecker and had a great feedback score and he said if I had any issues that he would refund my money. I didn't end up buying it for financial reasons at the time but you need to find someone like that. Otherwise if you buy second hand from any dude who advertises on gumtree or a forum, then you are just taking them at their word, which you'd assume most of the time is good enough but there are risks.

 

[swingn_wasabi]

Buying anything 2nd hand comes with a inherent risk.

As stated above, if you are dealing with a reputable seller / store, then there should be some sort of after sales support.

The only thing that I would mention, is that if you are employing a 3rd party to install (Or you are installing yourself), should something go pear shaped, you are likely to land up playing the "blame game" - IE: Must have be an issue with your installer, not the part etc etc etc.

For reference, I know Walkinshaw Newcastle gave me a price of $1900.00 for a 3.45 ratio diff for my ute supplied & installed... Personally haven't done much reasearch other than that, so I have no idea what they are going for 2nd hand nor do I know how much labor costs to install would be.

 

[mikey-]

When you turn the input flange, both axle flanges should turn at the same time, in the same direction. This should mean it is an LSD.

Next job, turn the input flange 3.45 revolutions (approx 3.5 anyway). This should make the axle flanges do 1 single revolution. That is how to check the ratio.

Hold any of the flanges and check that there isn't a very large amount of backlash.

If he'll let you check the oil make sure it has no metal fragments in it.

And you can do all these checks, but until it's in your car you wont know if it's going to whine like crazy

 

[Yonnee]

When you turn the input flange, both axle flanges should turn at the same time, in the same direction. This should mean it is an LSD.

Just turning the input shaft (pinion) will turn the whole crown wheel, which will in turn spin the whole diff centre and spin both axle flanges in the same direction, irrespective of whether it has an LSD or not.
It's when you turn one of the axle flanges that an LSD centre will spin the opposite flange in the same direction, or the opposite direction for an open centre.

 

[mikey-]

Thanks for correcting me, I knew I did something along those lines when I was buying my last diff.

 

[Turtle2388]

Wondering what's the point of doing this? What's the difference between manual and auto diff and what would happen if you put a manual diff in an auto?

Sent from my GT-I9505 using Tapatalk 2

 

[mikey-]

The manual and auto have different gearbox ratios, so to make them drive similar on the street they have a different diff ratio.

Basically the manual 3.45 diff will liven up his auto car by shortening the gears.

 

[RoaringSky]

Best bet is to bring a mechanic with you to check the diff for backlash and end float on the pinion, then smooth rotation and freeplay on output flanges. They all need to be free spinning but firm and smooth. With minimum end float and 1/4" backlash max.

 

[VE_CalaisV8]

Wondering what's the point of doing this? What's the difference between manual and auto diff and what would happen if you put a manual diff in an auto?

Sent from my GT-I9505 using Tapatalk 2

Currently he has a 2.92 ratio diff. This means its slower acceleration but it is revving lower at highway speeds. Pretty much more comfy and liveable. I have this ratio and at 100kmh im sitting on 1600rpm. If he changes to 3.45 gears, his off the line acceleration will greatly improve but at the sacrifice of top end speed. At 100kmh he will now be sitting on 1900-2000 rpm which is still fine. HSV gears are 3.70. Some people even like to go to 4.11 but then you are sacrificing fuel economy and cruisiness at highway speeds. So 3.45 or 3.70 are spot on if you want that extra kick off the mark.

I know that GM motorsport in Melb do a total diff swap over for $2k.