NZ 300ZX Owners Club Forum

[MikeC]

A lucky break meant I got my hands on a close ratio OS Giken gear set in a 300ZX box. For those of you who remember patriot you will know what I am talking about.

For the younger folks, Patriot was a 300ZX that came into NZ heavily modified from Japan many years ago. TD06 turbos and custom manifold etc etc.

It ran occasionally but at the moment it needs some engine work so the gearbox was sold to me hopefully to fund that. The owner being the good guy he was wanted to make sure I was happy with the deal so Glenn (Mungy) pulled the box apart so we could check it was what was expected.

Good news and Bad news



Good news was it was an OS Giken close ratio kit. It changes the ratios as follows
Stock OS Giken
1 3.214 2.695
2 1.925 1.703
3 1.302 1.236
4 1 1
5 0.752 0.752

Bad news was two things

Firstly a broken Shift fork


and secondly worn slide hubs.

We think this is what also caused the broken shift fork, because it is difficult to get into gear with the worn slide hubs, we think an 'over keen' mechanic forced it into gear and broke the shift fork.

Now worn slide hubs are what cause the notorious fourth gear grind we all hear about.

What it actually is the teeth on the slide hub getting worn and making it harder to go into gear – to line up all the necessary teeth.



This is the slide hub

This shows (sorry about the crap photo) the worn points.



So no big deal you say just buy a new slide hub and shift fork – bolt it in and away we go.

So I contacted all the major US firms and the local Nissan dealerships and Courtesy Nissan and everyone else I could think of and they all said the same thing. This part has been superceded you need to buy the new 1996 (or Series II) version.

Now I had heard this and basically any problem with a 300ZX gearbox you are told to buy the new internals. Well they are pretty much the same cost as a new gearbox so you might as well buy those.

BUT that did not work for me as I had a OS Giken kit and they are made for the Series I gearbox. So even if I bought the new internals it did not allow me to run the close ratio.

So Bugger…..

But then one of the US suppliers (who will currently remain nameless) said they could supply the Series I slide hubs.

I was so excited I bought seven of them. Yes seven of them!!

I knew a few guys that wanted one, I had a couple of gearboxes with the 4th gear grind and of course the Os Giken gearbox.

After waiting very impatiently while their gearbox supplier fluffed around, and then NZ Customs mucked me around even more they finally arrived.

WOO HOO – but no they were not the same



Turns out they were the series II slide hubs. Which by the way are the same as the Nissan Terrano (or appear to be based on the parts numbers). But as you can see from above the widths are different and ridges are different and basically they don’t fit at all.

And I have seven!!! Sure they did offer to take them back and they have been good about it, and the person who did not pay attention to my request no longer works for them.

But I still have the same problem.

So we decided to modify them and try to make them work.

First we did a hardness test. Turns out Series II hubs are a lot harder than Series I.
Then we got them milled down to the right width. Then we had to trim every notch to put back the points. Then we hardness tested them again. They were not as hard as before, but still harder than Series I.



Then we had to send them off for spark eroding so the Series I clips would fit. Took ages and lots of money.



After all that gears which originally cost $175 each are now up to $500 each and that’s doing all seven at the same time to save costs.

Just today went for a quick drive in Z with the OS Giken kit and it shifts smooth as silk. The ratios are great and you always seem to be on boost. Will be testing it in anger at a race track soon.

If someone wants to fix the fourth gear grind in their gearbox, I have a few of these for sale refer business classified.
http://www.300zx.co.nz/phpBB2/viewtopic.php?t=5368

[Mad Mike]

Exellent post Mike - good info and good story, thanks for spending the time! Be keen to hear how you go "in anger". Cheers, MM.

[Zeeman]

any chance you could let us know when you are going to give it a go in anger? if it happens to be at Hampton downs or Pukekohe I would be keen to come and watch for a bit. always nice to see your race cars in action
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it is surprising how well things bounce at 50kph

[fome dome]

That pic with the broken selector look familiar Brett?
brings back memories
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If there's a bird behind me Murphy its going to bite me on the prickle!

[Zeeman]

[MikeC]

[MikeC]

Very wet day at Hampton - but car and gearbox ran flawlessly.

[Heretic]

When are you running at Taupo next? Its a bit closer to home for me LOL
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My kit car is not a 300ZX, but it does use a 300ZX steering column - does that count?

[MikeC]

17 october at taupo for the ford muscle car club day