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Discussion Starter · #1 ·
It's about time for me to remove my original gearbox. The 5th gear grind and bearing whine are beginning to get the better of me.

The present gearbox is an FM54-501 with 200k miles. Still shifts great except for grinding into 5th when cold.

I've found several good deals on low-mileage FM55-505 gearboxes. I know the gear ratio of these will be different. That being said, If I were to consider putting a 9-3 gearbox into an early ('94) 900S, what might I need to consider? Do the car's share the same inner driveshaft splines/diameters? The 9-3 uses a hydraulic clutch but I'd likely back-convert it to a mechanical.

Any ideas? Any hints on gear ratios between the two boxes?
 

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Discussion Starter · #2 ·
Okay, did a bit more research. The gear ratios are as follows:

Original Gearbox (FM54-501):
1st: 3.38
2nd: 1.76
3rd: 1.12
4th: 0.89
5th: 0.70
FD: 4.05

9-3 Gearbox (FM55-505 or FM55-507):
1st: 3.38
2nd: 1.76
3rd: 1.18
4th: 0.89
5th: 0.66
FD: 4.05

The 9-3 gearbox is nearly identical in gear ratios with the differences being a wider 3rd to 4th split and a higher 5th gear ratio. This out to give me slightly better highway economy.

And comparing gear speeds:
FM54-501:


FM55-505/FM55-507:


It looks like about a 400 rpm drop at interstate speed. Not bad, though, passing power at anything under about 65, in 5th, might suffer.

So that being said, it looks like gear ratio isn't a problem. I'm sure the gearbox will bolt up to the 2.3 block. Can anyone confirm that the input shaft splines are the same? Also, can anyone confirm that the '94 driveshafts will work with the newer gearbox? Thanks.
 

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well i recall Dimitry using a 9-3 gearbox in one of his cars. he also retrofitted the hydraulic clutch in his car. you'd need the pedal and other parts, and then have to drill to mount the pedal, but there's already a nipple on the bottom of the brake fluid reservoir to attach the lines for the cylinder on the new clutch pedal.
 

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Dimitri's install looks pretty straight forward. I would ytake the extra step of adding the hydraulic clutch too. I think the reliability of it outweighs the extra time/cost.

I wonder why 3rd and 5th are different. What did they gain there?
 

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First off if your going to scale your graph's for comparison make sure you scale them the same way so that it is easier to compare slight differences. The 9-3 gearbox has updates that make it a little more stronger.
 

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Discussion Starter · #6 ·
Nahum; I used a little dos program for quick comparison of speed based on ratio, Car Test. It auto-scales the axis without my control and, being an OLD dos program, I cannot change the axis to suit my needs. The point was to show the changes in speed with the gearing; anyone looking at the graphs can see that there is a difference in 3rd and 5th gear. I didn't think I needed to spend any time loading numbers into Excel to generate new graphs. What you're seeing here are screenshots from Car Test.

Do you know if the shafts are the same spline diameter, etc? Looking at Demitri's site, it looks like his shafts slipped right in without trouble. Does anyone know of any differences in sizing between the early and late NG900's?
 

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Sorry no insult meant. Differences in axis labeling when graphing the same data families is a pet peve of mine; my apology for how it came out.

As to any knowledge in differences in splines I do not think there are any to my knowledge.
 
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