With a successfully finished STAGE-1 and some trackdays already done with the modified car it is now time to talk about the ‘dark side’ of the new gearbox : its final drive is fuc**** too long !!
The general stepping between each gear is really good but final drive ratio doesn’t help at all to stay in the good power range when driving hard on track. Of course I would have installed directly a shorter final drive equiped ITR S80 gearbox if prices on the used market were lower !
Staying like this is not possible so I started studying the available options to swap a new final drive into this transmission. For a budget reason, I decided to look for a used final drive. Because LSD found into both S9B and S80 gearbox are exactly the same I moved on a classified talking about a ‘JDM ITR S80 4,785 final drive’. Exactly what I was looking for …
… but a big mistake on my side. You’ll see why just a few pictures later.
So first, let’s start the job with my first gearbox opening !
I will not use this article to explain a general rebuild of the transmission as I have no bearings or synchros engagement problems.
So there will be :
- New OEM Honda rear light contactor
- Spoon magnetic oil plug with new seal
- New OEM Honda axles seals
- New FD shaft bearings as the old ones will be removed with the press
And main components removed. On the right is the used final drive purchased and on the left seats shaft and LSD.
Removing pinions from the shaft. Remember : stay organized ! This is really necessary here as you have to follow your workshop manual step by step and take notes of everything :
- how parts were linked together
The shiny machined area just on top of the final drive gear are different :
- Not the same diameter
- Not the same height
- Not the same shape
In fact, the explanation is easy when you don’t make the mistake I made with the 2 differents workshops and transmission views.
On the left, the S9B shaft receives 2 half needle bearings and the first gear just over it. And that’s it, the gear should rotate freely.
On the right, the JDM S80 shaft receives a fully circular parts and ‘then’ receives 2 half needle bearings and the pinion.
All references are different and not compatible. So YES you can install a 4,785 ITR final drive straight into your S9B gearbox but THIS MUST COMES from a EUROPEAN S80 gearbox (not from a JDM ITR S80 gearbox).
So so so … after a few days of searching on the used market and thinking about buying a brand new final drive I decided to move on the second solution. But I need to make a good investment ^^ !
I turned it into an hardcore purchase option and ordered a brand new Mfactory 4,923 final drive ! With like I said new ball bearings for the shaft.
With everything ready time to start the new FD installation. Again, double check EVERYTHING to avoid mistakes !!
You will feel really bad if you forget something with the gearbox already back on the car !
FD shaft finished. There’s a specific control procedure well explained in your workshop manual for the tightening sequence of the top nut with clearance controls between gears.
And something really important : NEVER USE A COMPETITION GEARBOX OIL RANDOMLY BOUGHT SOMEWHERE !! You think it will be better for your transmission but you can really face the opposite effect …
Let’s talk about what I know : Honda. They use a ‘fluid’ oil in their gearboxes because the DESIGN of the internals needs it (guides, oil holes, …). If you buy a quality performance oil which has a higher viscosity for exemple you’ll destroy everything inside as bearings will not be lubricated.
I have an EF civic as a daily drive with OEM DOHC ZC engine and gearbox. This is not LSD equipped but has a normal open differential. I’ve always used new engine SAE 10W40 into both engine and gearbox and it runs smoothly. Same on the CRX when he had the stock engine.
You need to use Honda MTF3 in a LSD equipped gearbox for a simple reason : this oil is close to the 10W40 described just before but it contains the necessary additives for the LSD.
For other brands, models, … check your workshop manual guys or go discuss with your dealership !