Ok guys, as changing the diff gears in your car is one of the best ways to increase acceleration, and is a very common thing to do, I thought I would do a bit of a write up for the people that would rather source the different gear ratio’s themselves, rather than just buy them off eBay or brand new from a performance shop, as it can get quite expensive that way.
This will basically only apply for the people that own a VL – VTs1, as the later models use bigger gears and aren’t cheaply available from the wreckers.
I would also like to get a list happening of what gear sets are available from what models, which will fit the VL – VTs1 diffs.
The gears are exactly the same in live axel and IRS diffs so that’s no problem.
This is what I have so far, will add more if there is more to be added.
3.08:1 – VL V8’s, and 99% of VN-VTs1
3.27:1 – VP GTS
3.45:1 – VL 6cylinder models
3.73:1 – R31 skyline (Very rare, need conformation on exactly what models they are in, I was told they are in all manual R31’s, that is not the case, I have also heard they are only in ’91 and ’92 models but cannot back this up)
3.91:1 – R31 Skylines, auto R31 Pintara
4.11:1 – Manual R31 Pintara
I would also like to chuck this link in as immortality has done a great write up and will answer many of your diff related questions.
diff, all you need to know
Anyways, back on to it. What I did was just head down to the local wreckers and pulled a diff out of an R31 with a 3.9:1 ratio diff.
Firstly I took the diff cover off and inspected the gears as best I could, as I didn’t want to buy a diff and realise the gears are all worn and chipped and what not.
The diff really isn’t hard to get out, just basically look at what is holding it up, and undo the bolts that you see, there will also be a brake line and what not attached to it, as you don’t need any of this just cut it off. Also take off the brake callipers and rotors as you may get the diff cheaper that way and you don’t need that crap for anything.
I find it easy if you undo everything holding it up except the 2 bottom shock bolts, that way you can get everything ready to come up but the diff will stay supported by the shocks, then finally knock the shock bolts out and the diff will drop out.
The diff I got cost me $110, which im sure a lot of places you can get it a bit cheaper.
Some of the bolts are quite large, 24mm if I remember correctly so take plenty of decent tools with you, make sure you take a good sized breaker bar; they are the best things ever.
When it was home again, I started taking the gears out, really not as hard as I was expecting either.
Step 1 – Undo the pinion nut…
This nut is huge (27mm) and took a bit of effort to get it off.
Its tricky because when u turn the nut, the whole pinion moves with it.
What I did was get a scrap bit of steel I had lying around, drilled 2 holes in it to match the holes on the pinion flange and bolted it to that, refer to the pic.
And then had it lying on the ground with my foot firmly on it, had it set up so when I put force on the nut, the steel plate would hit the ground and not allow the pinion to spin, therefore letting the nut come off, refer to the second pic.
It does take a bit of force, but nothing crazy, unless you’re a girls dick, but you will need a decent sized breaker bar to get it off.
Step 2 – Remove Axles
Pretty simple, you will see 4 nuts that hold the axles in, basically just undo them; you will have to get a screw driver or something on the other side of them to stop the bolt from spinning around.
Once all 4 bolts on each side are off, just get a crow bar or something similar and just wedge it in there and lever it so it pulls the axles out, they come out with hardly any force needed. Then remove them completely and put them aside.
Step 3 – Remove diff cover and diff centre
Pretty simple once again, just undo the 9 bolts holding the diff cover on and remove the cover. Once inside, you will see 4 bolts holding in the bearings that hold the centre in place. Remove those bolts as well.
Take the little brackets off and then its time to pull the centre out, what I did was get my crow bar in there and just lever it to pull them out, once again, not much force is needed.
Step 4 – Remove pinion gear.
Firstly you will need to remove the pinion flange; this is a bit of a prick, as is pressed onto some splines which mine was on there damn tight.
I still had the steel bar on there from the start, so basically all I did was hold that tight and smack it with a hammer from the under side about 200 times and it came off
.
Once that is off you will see the pinion gear is only really sitting in there snugly with a bearing, all I had to do was smack it out with a hammer, but I put the pinion nut back on the top so I didn’t damage the thread or anything, and it came out easy enough after a few hits.
Step 5 – Removing crown wheel from diff centre
Place the diff centre in a bench vice nice and tight, and remove all of the crown wheel bolts.
*Note: These bolts are left hand thread (Reverse to normal)
The crown wheel won’t just fall out now; you will have to ease it out.
I used a hammer and a cold chisel and just lightly tapped away, moving in a circular motion around the crown wheel so I didn’t damage it, after a few laps around it, it should just drop out.
And there you have it… Crown wheel and pinion gear are out!!
Should save you a bit of cash in the long run, now you just have to put these gears in your diff, I wasn’t keen on doing it myself as there is a fair bit to adjust and get perfect and I don’t wont something to go wrong in this diff.
For a reference it’s costing me $330 to swap the gears over and replace all the bearings and seals.
Hope this is some what of a help to some one, and I should also add that this is just the way that I did it, I’m sure there is many better ways to do it, but this worked for me.
Also…. I take no responsibility for anyone that stuffs anything up or hurts them selves in the process lol.
If you have anything you would like to share, just post away, any useful info I will add to this post.
Cheers,
Geoff
How to: Source your own diff gears and remove them yourself
- A good sign its well aged