Part 2
VSS and Options
As many of you have heard, yes, the VSS is located in the differential, rather than the transmission.
Some of you have speculated that some 6MTs have a plug covering what looks to possibly accommodate a VSS. This is true and false. Yes, the whole is the right size and shape. No, because the plastic gear that turns the VSS is absent from the output shaft. One would need to purchase the plastic gear (and a ball that locks the gear in place) and dissemble the transmission to install it.
Some 6MTs don't have a plug. They may be cast molded shut.
Here we see one 6MT has a plug and the other does not.
So what are the VSS options?
1) Purchase and install the plastic gear (as mentioned above) and use the pertaining S13 or S14 VSS.
2) Install a differential that has a VSS in it. This is not limited to the S15 differential. From what I've seen, a Q45 differential has a VSS and may be used.
3) Custom magnetic pick up or gear tooth pick up and sensor attached to the driveshaft.
So what are the signal modifier options for the speedometer to read appropriately?
If option 1, then you won't need anything. If you're using a S13 cluster, then use a S13 VSS. Likewise for the S14.
If option 2, you can either use the S15 ABS control unit (located next to the ECM) or use an aftermarket signal modifier such as the Dakota Digital box or Innovate DL-32.
If option 3, you will need an aftermarket signal modifier.
Neutral Position and Reverse Switches
Wiring the transmission to continue using the reverse lights is very easy. No explanation should be needed here.
Gearing and Specifications
Gearing Comparison to the 5MT
Necessities to Use a 6MT
For the SR engine ONLY.
- S15 Transmission Cross Member. The 5MT and AT cross members will not work.
- Transmission Mount. The 5MT and 6MT mounts are all the same.
- 6MT Flywheel. The 5MT flywheels will not work.
- Clutch Disc and Pressure Plate. If one is using the OEM S15 Dual-Mass Flywheel, then feel free to get an unsprung clutch kit, but this may be costly. Sourcing a new OEM replacement clutch kit is rather difficult to find. You can use a sprung clutch kit, but the dampening will be overkill and shifting between gears may feel sloppy.
- Clutch fork, Release Bearing and Holder, pins, and slave cylinder. I am not 100% here, but they appear to be the same between the 5MT and 6MT.
- Driveshaft with S15 output. (Unsure, but the OEM S15 driveshaft may be used as long as the S15 or similar differential with VSS is used.)
- Shift knob with M12x1.25 threading. The 5MT shift knob won't fit because it is thinner, M10x1.25.
Aftermarket Options
- Driveshafts. Driveshaftshop.com seems to be the place to go.
- Flywheels & Clutch Kits. This may get costly, but one can either source a used Autech flywheel (~$400), purchase a new JUN flywheel (~$700), or purchase a clutch kit that includes a new flywheel (~$1100+). The benefit of getting the Autech or JUN flywheels is that you can continue using a 5MT clutch kit, whereas a complete clutch kit such as the Nismo Coppermix may force you to stick with the same disc.
- Gears. Nismo, OS Giken, and possible others make gearing kits for this transmission. These kits are rated to withstand more power.
- Transmissions. Nismo and HKS make complete replacement transmissions. The Nismo transmission costs ~$3500, but only guarantees quality up to 298lb-ft. The HKS transmission costs ~$10500. Both, however, have different gear ratios compared to the S15 MT.
Comparison between the Nismo 6MT, S15 6MT, and 5MT.
Miscellaneous
- Nismo 6th Main and Cross gear swap
I swapped out the 6th gear on one of my 6MTs for track use. It brought the gearing much closer to 5th. (Gear Ratio changes from 0.764 to 0.8624)
- Closer look at Autech Flywheel
If I recall correctly, the OEM Dual-Mass Flywheel weighs about 28lbs, and the Autech Flywheels weighs about 17lbs. Also, the Autech flywheel was engineered by both Nismo and Exedy. Both of their stamps are on the flywheel. (The clutch disc pictured is the Fidanza 3.2 Clutch Kit).
Final Notes
Some of you guys jump the gun by saying, "forget the 6 speed, its weak anyway.." but most of you guys never used, touched, or seen a 6 speed in your life. Please don't continue making this your automatic response when the 6MT is mentioned.
How come this guy with 400WHP hasn't destroyed his 6MT when I only have 340WHP and destroyed mine in weeks???
Assuming you know how to shift, it just depends on two things.
- How much TORQUE are you putting out? Not horsepower... One guy may do 340WHP and have 280WTQ while another may have 340WHP and 320WTQ...
- What are you using the transmission for? Drifting??? Drag???? This transmission is not good for that.
Nissan designed and guaranteed the quality of this transmission when torque input is no more than 209lb-ft. This is because Nissan (as well as any manufacturer) designed the transmission with a Factor of Safety or Margin. So, under normal conditions or even if one were to push an unmodified Spec-R to its limits, the transmission will not fail.
I estimate Nissan has a margin of 1.333. So one can expect an actual limit to failure at about 260-270lb-ft. The gears are very fragile to impulse. I figure one could shear some teeth with an impulse of 250lb-ft. To create an impulse, one could simply clutch kick. If one were to transition smoothly, no impulse is made, and the oil used effectively fills the gaps between the teeth of the gears, then this transmission may be capable of 310WTQ.
Keep in mind that the OEM S15 flywheel is a Dual-Mass flywheel. This flywheel significantly reduces an impulse, making engagement incredibly smooth and allowing the gears to withstand more torque.
Fitment On Other Engines
- No.
Hahaha. This just isn't the transmission to bother with that. The amount of work it would take to re-center the input shifter of the transmission to a KA engine, create a sandwich plate to marry the engine to the transmission, make sure the clutch fork will pivot in the correct range to release the clutch disc, and align the starter to line up with the flywheel, is just too much to bother.
Sources- 1999-2002 Nissan Silvia S15 Factory Service Manual
- 1991-1994 Nissan 240SX Factory Service Manual
- Nissan S15
- Nismo (Source Not Found)
- Review
