ashley
knowles.net

Briefly mentioned this on my blog a long time ago, and have had a few people asking me about it.

I own an S15 Silvia, which came with a 6 speed manual gearbox – notorious for breaking. Even the other SR20DET gearboxes in the S13 and S14 are known to break easily when some decent power is pushed through them.

Doing a gearbox conversion is recommended for anyone doing track work – drift, drag or circuit.

As I had fried the clutch in my S15, I was looking into a longer term replacement – I settled with an OS Giken STR Twin Plate clutch. This baby wasn’t cheap, but.

Running this clutch with the 6 speed would surely smash it to smitherines, so the gearbox had to go. I had previously had the circlip, holding 4th gear in place, welded up, to stop it from falling off, as is common for this gearbox. But I wasn’t going to trust it.

So I decided to run with a Z32 gearbox conversion. A mate of mine, Shane Blank, who owns the IDR46 S14 200SX drag car, had done the same conversion with no issues, so it was a goer.

There’s two options in doing the conversion, in terms of the kit you can get, price, etc. Shane chose the kit from Mazworx, a company in the USA who pioneered the conversion kit. I chose to run with a local kit, produced by Nigel Petrie – “Nigel” on the NissanSilvia.com / Hardtuned.net forums. The kits are almost identical, although the Mazworx kit gives you the option of supplying tailshaft etc.

The kit I received from Nigel included:

• An aluminium adapter plate – bolts to your engine, and then the Z32 gearbox bolts to it.
• Gearbox cross member
• Gear shifter bracket
• Gearbox shifter hole cover
• Machined bellhousing – I sent the bellhousing I had back to Nigel in return.

The kit cost me around $1000 AU with the machined bellhousing. I also had to source a gear shifter – a mate of mine had one she wasn’t using so I grabbed that for free.

I sourced a Z32 gearbox from a wrecker in Melbourne, who shipped it up, with a Z32 half tail shaft, for $950 delivered.

The tailshaft was required (sort of) to have a new tailshaft made up to suit my drivetrain. The S13/S14/S15 tailshafts may be different lengths?

Driveline Services Australia whacked together my new one piece tailshaft, for a sum of $650. Turns out I probably didn’t need to grab the Z32 half tail shaft with the gearbox, but oh well.

With the S15 originally running the 6 speed gearbox, the standard clutch is also different to that run in the S13/S14, in terms of it’s size (not so much diameter, but the depth from the engine side of the flywheel to the front of the clutch cover plate). To run the Z32 gearbox, you need to run an S14 clutch on the S15. For S13/S14 this obviously isn’t an issue. My OS Giken clutch is, therefore obviously, to suit an S14. You will need S14 flywheel bolts to run this.

The kit itself is pretty simple to install. Bolt the adapter plate to the engine. Install clutch/flywheel. Install gearbox, tailshaft, etc etc.

The S15 has a speed sensor at the rear of the car, built into the diff housing, so you don’t need to wire up the Z32 sensor, which is installed in the gearbox itself.

You will need to hard wire in the reverse and neutral sensors to the stock wiring. The plugs don’t match up unfortunately.

The gear shifter for the Z32 box requires a hole to be cut in the gearbox tunnel. Using the hole cover plate that comes with the kit, you can mark out where to cut (an appropriately sized hole saw will do the trick). The hole sits in the same position for all the S13 / S14 / S15 chassis’. It’s around 5-8cm back from the centre of the original shifter, if I recall.

In my case with the S15, I had to smash the gearbox tunnel up around the firewall so the Z32 box would fit in the tunnel. The problem was more so installing the gearbox then the gearbox fitting, as you have to “slide” the gearbox in from the back so as the input shaft slides into the clutch. This is next to impossible without bashing the tunnel a bit…