Differential Ratios

[sambo]

Thanks Warren. I'll hunt around for an S15 diff and won't get the tailshaft made until this is done. Excellent info, thanks.

Merv, KAZ is just an aftermarket manufacturer and there are quite a few due to the popularity of Nissans for drifting. Nismo is another one and a quick search found this. I don't know enough about it and I suspect that a complete S15 rear end can be bought from a wrecker for less, when you consider freight, GST, etc from Japan.

I'll make a few phone calls around Melbourne tomorrow if I get a chance and see what turns up. As Mike's numbers showed on the other page, it's well worth it for highway cruising.

That's it Merv. I left out an 'A' in their name. I spoke to a Jap tuning shop down here last year and they could get them a lot cheaper. Just need to find them again.

[Merv and Sharon]

Thanks Sambo. I would be interested in how you go: Not keen on removing the whole rear suspension but replacing the differential internals and using the same shafts (on the R33) seems possible with the S15.

Merv

[WKB]

Merv,
You don't need to remove the suspension to remove the diff. Unbolt the axles, remove a few bolts holding the diff in and it drops out from cradle. The complete diff you choose to use fits back in the cradle( after any mods). There is no reason to pull out the internals.

Warren

[sambo]

Merv, after reading forums and speaking to a few wreckers around Melb/Syd I've decided to go with the S15 diff conversion. You need the complete diff and half shafts (outer CV joints) from a 6 spd manual S15 200SX, which is a straight swap with the R33 diff/shafts into your existing housing and gives you a 3.692 ratio. We may need to swap the diff backing plate too but that's easy. Mine's coming from Sydney and I should have it fitted over the weekend.

[Merv and Sharon]

Thanks Sambo. So one changes the diff (internal) and the half shafts and outer CV joints as well? I have already called one place with no luck, but will start soon in earnest. Can you send me a PM with an approximate cost range - so that I have a starting point with these guys?

Merv

[sambo]

Merv, you just pull out your axles (half shafts / CVs), unbolt the R33 diff from the cradle and replace the whole assembly with the S15 assembly including half shafts. If backing plate mounts are not the same you may need to swap that, as mentioned.

Speak to Bill at On Boost Parts in Sydney - 02 9709 2992. $225 for the diff, $100 for each half shaft and $100 freight to Melbourne. He left the oil in it and wrapped it up without cleaning - car was written off with only 35,000km - so I could be sure of its condition.

Edit: reason you need half shafts as well is because R33 has 5 bolt flanges and S15 has 6.

[Merv and Sharon]

You are a good one Sambo!

Merv

[Pecal]

Merv,

Sambo's right on the money with the diff change. The only other detail is the forward mounts on the S15 diff housing. You will need to make bushes and spacers as they differ to the R33.

[Merv and Sharon]

OK ... any pics of those around?

merv

[sambo]

Merv I'll post a few photos after I've fitted mine. It ships tomorrow morning and the freight company said 90% chance it'll arrive Melbourne on Friday arvo. Fitting it Saturday with a bit of luck.

Have you made up the tailshaft yet? Might be worth holding off until this conversion is done!

[Merv and Sharon]

That would be good Sambo. I called those guys and they have one aside for me from a 2002 Silvia that was a front end collision (44,000ks) with half shafts and "diff centre" (I will need the backing plate as well I think. Did you get the entire rear suspension?). Is that all I need? Price seems same. I will check mine again tonite to make absolutely sure that it is an R33 and then order the S15.

Merv

[sambo]

Merv, the backing plate comes off your R33 diff, since it is matched to the mounts on your R33 cradle. Put that onto the S15 centre if it does not mount straight up.

No need to buy anything other than the diff and axles as I understand it. The whole family of S13/14/15 plus R32/33/34 diffs use these R200 centres and are interchangeable - sometimes the diff swaps over by itself, other times like ours you need the axles from the donor diff. They vary by no. of splines, shaft length, flange bolts, etc. Checkout the Skylines Australia forum, it's a wealth of info.

I've been reading up on diff oils and you need LSD oil in the helical (6spd manual) version. I'm getting Castrol EPX 80w90. You need 1.5L to 2L.

[Merv and Sharon]

OK and thanks again, I will order tomorrow. I do wonder how the car will drive after this. It is a big change.

Merv

[sambo]

Lower rpms on the highway? Slightly less pickup, but would you really notice it in a Cobra? You'll probably put the power down a little easier if anything!

The viscous (R33) centres were described to me as operating more like an open wheeler when you're corning hard or with one wheel off the ground. These mechanical ones are meant to be better at transitioning torque from side to side and closer to a 1.5 way diff (semi-locking). Plus you get to say the word 'helical' a lot, which sounds really tricky to me.

Merv, even more tricky, check out these high capacity diff casings for when you go drifting in the Cobra!

http://www.driftshop.com.au/diff.htm

[Merv and Sharon]

These look to be good final drives Sambo. I did some calculations using: http://www.mustanggt.org/gttranny.htm

and

http://www.kabamus.com/garage/gears.html

With my tyres 275/40/ 17 and my final drive is 4.1 by the part number

With the standard set up I should do about 2300-2500 at 100km/hr (my iPhone GPS measurement in the car tends to confirm this too).

With the S15 helical final drive that would seem to come down to 2000 rpm.

Of course that could make a hole in acceleration (perhaps the THE key aspect of these cars) unless more power was produced thru engine mods and/or higher rpm (engine life?)

I am thinking that I will buy the S15 diff and shafts to put aside for now in case they become scarce. So I am really keen to see how yours goes. Warren of course has done this already (above). His driving experiences will be interesting to hear, although he has a different motor and transmission.

Merv

Merv

[stumpeater]

Just another point of view, I have a VY SS 5.7 Manual 6 speed, and I find the standard diff way too tall for a big car, (about 3.7, I think), Great on the freeway 100kph in 6th, only doing 1500 rpm and 9lts per 100km's But the problem is towing a 1.5 tonne trailer. Handbrake start on a bit of a slope, I've got to really ride the clutch to get it to move. Not that anyone will be doing much towing in a Cobra, but I am looking forward to my R33 4.1 (.3) If it's too low, I'll just use second gear to start. Should do nice burnouts in first, though!

[WKB]

Originally Posted by Merv and Sharon

Of course that could make a hole in acceleration (perhaps the THE key aspect of these cars) unless more power was produced thru engine mods and/or higher rpm (engine life?)



Merv

Merv,
I have my S15 diff sitting under my bench for about 18 months for the reason you stated. The motor I have is only 4ltrs, but will rev to 6500rpm easily, which makes 1st gear usable with a 4.1:1 diff(and fun to drive). Once I bolt on the supercharger I will be changing the diff over.

The price you were quoted is a very good price and these diffs will only be harder to come by in the future.

That picture Sambo attached looks as though it is a S15 diff. Note the position of the ABS sensor behind the drive flange and the 6 bolt flanges on the drive shafts.

Stumpeater,
The Cobra that I know that has had the S15 has a T56 and did take off in 2nd gear all the time with the R32 diff.
If you are going use Ist gear as you described, replace the front rubber bushes with steel bushes. I have been told that it is not a pretty sight if the bushes rip out under acceleration.

Warren

[stumpeater]

Originally Posted by WKB

Merv,


Stumpeater,
The Cobra that I know that has had the S15 has a T56 and did take off in 2nd gear all the time with the R32 diff.
If you are going use Ist gear as you described, replace the front rubber bushes with steel bushes. I have been told that it is not a pretty sight if the bushes rip out under acceleration.

Warren

Good Point Warren, Thanks, Peter.

[Merv and Sharon]

Thanks Warren. Sounds sensible for me now too. I already have a drive shaft that fits between my T5 and the existing R33 diff. It would not need to be changed I assume?

Merv

[Merv and Sharon]

Exactly how do you calculate a diff/final drive ratio (without counting gear teeth)? I put a mark on the drive shaft near the diff housing and some tape on a rear wheel relative to the edge of the body/sill. So the final drive is the number of rotations of the drive shaft produced by one wheel rotation? I multiplied this by 10 to get some better accuracy and 10 wheel rotations produced 22 drive shaft rotations (in neutral). FD = 2.2 therefore???!!!@@## It has been a long day and the brain is obviously missing something very simple ....


Merv