xpertsnowcarver

S15 6 Speed Manual Transmission (6MT)

***Sorry if the photos no longer show up. Photobucket turned into a real shitshow of a site and wants me to upgrade to a $400 account. I'll figure out how to host them somewhere else.







Everything you wanted to know about the S15 6MT. A lot of this information is scattered all over the place. I'm just bring it together. I personally know quite a bit about the 6MT. I own and use two of them.

Please do not ruin this thread with a bunch of nonsense. Don't post information unless you are 100% positive that it is correct. Don't post how weak you think this transmission is, especially if you've never used or destroyed one yourself.. Any personal experience with this transmission is encouraged to be posted on this thread. For example, "XXXWHP and XXXWTQ, and I destroyed 3rd gear," or "XXXWHP and XXXWTQ, and she still kicks ass."

THE KA 5MT AND SR 5MT BELL HOUSINGS ARE NOT THE SAME.

I don't know everything, but I do know a lot. I'm not stubborn with what I am presenting to you. If you feel I posted incorrect or misleading information, I would be more than happy to hear you out and further research the issue.

To be covered:
- First look
- Comparison to the '5 Speed Manual Transmission' (5MT)
- Gearing and Specifications
- Gearing Comparison to the 5MT
- Necessities for Use
- VSS and Options
- Neutral Position and Reverse Switches
- Aftermarket Options
- Miscellaneous
- Final Notes
- Fitment on Other Engines
- Sources
- Post Notes

Pre-notes:
- I am strictly providing information regarding the S15 6MT for the SR engine. But, always take information as opinion anyway, and fact-check the information yourself.
- When I say 5MT, it is with assumption that it has a SR bell housing for the S13 and S14 SR engines and not a KA bell housing.
- When I am referring to a specific chassis, I will state so.
- I am strictly referring to OEM parts, excluding the 'Aftermarket Options' and 'Miscellaneous' sections.

Apparently the 6MT sycnromesh was designed by Borg Warner, just as the 5MT.


First Look


Nissan guarantees that this transmission will not fail at or below an input torque of 209lb-ft.

This transmission was designed with a Dual-Mass flywheel in mind. Watch this video for an animation on how the dual-mass flywheel works. The first half shows how it is assembled. The last half shows how it works.



Comparison to the 5MT
Similarities
- Bell housing pattern between the 6MT and 5MT are identical.
- The transmission mount is the same as the 5MT. However, the cross member is not the same.
- The slave cylinder, fork, pivot ball, release bearing, release bearing holder and pin all appear to be the same as the 5MT.
- The starters are identical between the S13-S15 SR engines.
- The 6MT clutch disc and pressure plate are similar to the 5MT. (NOTE: Because the 6MT uses a dual-mass flywheel, the OEM clutch disc is unsprung. The 5MT does not use a dual-mass flywheel, so the OEM clutch disc is sprung.)
- The output shaft to the driveshaft is the same as the 5MT.




Starters may appear different, but seem to mount and operate the same.

Differences
- The 6MT flywheel is much thicker than the 5MT. Consequentially, the bell housing is also deeper by the difference in thickness.
- The copper pilot bearing is located in the 6MT flywheel, rather than in the SR engine for the 5MT.
- The 6MT is divided into three sections, rather than two for 5MT. So, no! You cannot put a KA bell housing on a 6 speed.
- The 6MT shaft is slightly shorter than the 5MT shaft.
- The shifter and shifter plate are not the same between the 6MT and 5MT.
- Shift knob threading is wider, but have the same thread pitch. 6MT = M12x1.25. 5MT = M10x1.25.
- The Vehicle Speed Sensor (VSS) is located on the differential rather than the transmission.
- The 6MT cross-member is opposite of the 5MT. (The AT cross-member is closer to the 6MT, but still will not fit.)


Slight difference in spline thickness.


Thicker Flywheel. (In this picture, both the OEM S15 Dual-Mass Flywheel and Autech Flywheel are shown.)


This is the OEM Dual-Mass Flywheel with OEM Unsprung Disc and Pressure Plate. (If I recall correctly, the OEM Dual-Mass Flywheel weighs about 28lbs.)


6MT Crossmember and Nismo Transmission Mount


The 6MT bellhousing is noticeably deeper than the 5MT.


The shifter plate and assembly are completely different.

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 steel ball and c-clips that lock 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. This only works if you have a 6MT with plugged VSS slot.
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




***This last one I estimated where the Nismo 6MT gear ratio would be. The original can be found below.***

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. Any clutch kit for the 5MT will work, but if one is using the OEM S15 Dual-Mass Flywheel, then feel free to get an unsprung clutch kit, even though this may be costly. Sourcing a new OEM replacement clutch kit is rather difficult to find. You can use a sprung clutch kit on the Dual-Mass flywheel, 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.

Notes: It is best to install the transmission and engine together. With the 6MT mounted on the engine, it will not touch hit the chassis. But, because it is still fatter than the 5MT, there is less room to muscle the 6MT on or off with the engine already mounted. Don't forget, the flywheel is about an inch thicker, which means you need to pull the transmission about an inch further back. That's never going to happen... I've tried; there is no room for removing and installing the 6MT separately from the engine.

Everything else is straight forward and no different than the 5MT. Be sure to torque all bolts down to spec. They will shear if you over tighten them.

Parts to Reference


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.





Here are some more individual comparisons.

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 never used, touched, or seen a 6MT in your life. 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... (If the engine has a GT2871R, bigger intercooler, and injectors, then it should be fine. If you put a rebuilt the engine from scratch and/or put a 2.2L stroker kit, why didn't you buy a stronger transmission anyway? Even a 5 speed is a shitty tranny to mate with a built SR..)
- What are you using the transmission for? Drifting??? Drag???? This transmission isn't good for smashing gears like a mad man, especially with a very abrasive clutch. If you're engagements are smooth, the transmission will do fine. Most of you, and I mean 95% of you, aren't even close to 300whp. So destroying a 6MT transmission would be the last of your worries.

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. (Assuming the tranny is well maintained.)

I estimate Nissan has a margin of AT LEAST 1.333, so one can expect an actual limit to failure to be a least 270lb-ft (emphasis on "at least", because I personally know someone with 270WTQ and has no problems what so ever). The gears are fragile to sudden impulses. To create an impulse, one could simply clutch kick or drop the clutch from a stand still, but you'd need some very sticky tires and a very abrasive clutch. If one were to transition smoothly between gears, no severe impulse made, and the oil used effectively fills the gaps between the teeth of the gears, then this transmission would be capable of at least 300WTQ. (These are all ball park estimates.) Anything after that, beyond me. Have heard of someone with 340WTQ and not having problems... but this is second/third hand information.

Keep in mind that the OEM S15 flywheel is a Dual-Mass flywheel. This flywheel significantly reduces an impulse, making engagement very smooth and allowing the gears to withstand more torque. The Dual-Mass flywheel is quite nice, especially with the unsprung clutch disc. I honestly cannot tell the difference between a dual-mass flywheel with an unsprung clutch kit versus a regular flywheel with a sprung clutch kit (aside from the difference in rev response). I think the dual-mass flywheel with, for example, with the Fidanza 5.4 unsprung clutch kit would be an awesome combination. With the OEM unsprung clutch kit, there is ZERO clutch chatter.

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 shaft of the 6MT to a KA engine, create a sandwich plate to marry the engine to the 6MT, 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... you might as well do this for a sequential tranny, or some other heavier duty tranny.

Sources
- 1999-2002 Nissan Silvia S15 Factory Service Manual
- 1991-1994 Nissan 240SX Factory Service Manual
- Nissan S15 Specifications
- Octane Report - Nismo 6MT Conversion
- Dual-Mass Flywheel assembly and functionality - Youtube
- NISMO | Silvia•180SX Reinforced Cross 6-Speed Transmission
- Gearing and Assembly Prices and Comparison
- Parts List and Prices per Chassis

Post Notes
I think this transmission is a lot of fun to have, but not for drifting or drag racing. I use the transmission for road racing, and it has performed exceptionally well.

Again, please do not ruin this thread. Ask legitimate questions. Post solid facts and experience. If you have not used and/or destroyed this transmission, you're post/claim may not be valid to me.

Hope this helps a lot of you guys.

__________________

My YouTube Channel

onehundredoctane

Good info! Thanks for sharing!

Pure_JDM

Thanks for sharing...

anton1o

Amazing write up we don't even have this much info in AUS about the gearbox.

Thank You

Sent from my GalaxyS using Tapatalk

__________________

datsunnazi

finally some reliable info... i was tired of just hearing, "those trannys are weak! just use a z32..." ghey...

slider2828

Awesome write up! Always wondered about these nice little guys... I would love to have one...... Did you do the 6th gear yourself?

__________________
Turn and Burn!

MisawaJason

WOW, thanks for putting this out there in one place!!!

__________________
1 year tour in Korea = no car. FML.

xpertsnowcarver

No problem. There are some details I left out. I'll add them whenever I can recall them.

Edit: Holy fuck... Completely misread your post.

Yes, I do have the Nismo 6th gear installed on one of my 6MTs.

__________________

My YouTube Channel

xpertsnowcarver

Finally found the other graphs. These are much better illustrations.




Edit: I added a line for the Nismo 6MT in the original post.

__________________

My YouTube Channel

sidewaysil80

THANK YOU! i just picked up a 6sp/s15 spec r motor and have been searching and searching for info. i do have a few questions for you though...

-do you know the part number or where to buy the s15 cross member?
-will the s13/s14 transmission mount fit on the s15 crossmember?
-does the 6spd use the same transmission fluid as the 5spds?

xpertsnowcarver

1) 3137S-RRS50

2) Yes

3) Yes

~~~~~~~~~~~~~~~~~~~~~~~~~~~

Added a lot more information. More gear ratio comparisons and sources to reference.

__________________

My YouTube Channel

dorkidori_s13

i seriously <3 this thread...like A LOT!!!

awesome find in information man, threads like this should be made PERMANENT stickies!!! (ill recommend it for one actually)

__________________


Bought something from me??? POST A REVIEW HERE!!!

ManoNegra

Great info, props yo
I think an S15 SR w/ 6-speed tranny and mild boost upgrades would
make a killer daily


btw, how is the hand?

xpertsnowcarver

Thanks

Hand is doing much better. It was a clean cut, so it healed very fast.

~~~~~~~~~~~~~~~~~~~~
Started using the dual-mass flywheel instead of the Autech flywheel. I must say, this flywheel is pretty cool. With the OEM clutch disc unsprung and letting the flywheel dampen the engagement, there is ZERO clutch chatter. I highly recommend it for daily driving. It may play a major roll in extending the life of your transmission.

If you increase your horsepower to +300whp/+240wtq and are still using the dual-mass flywheel, I would recommend the ACT 6 Puck unsprung clutch kit as a good replacement of the OEM unsprung clutch kit.

__________________

My YouTube Channel

West

Thread stuck due to pure awesomeness.

__________________
West - Zilvia.net - Toyobaru.net - NapkinSketch.com

Om1kron

dope ass post Joel.

__________________
Wayne

Vatche

i agree thread is overkill. haha.

__________________
The Ultimate For Sale Thread <> Review Thread

xpertsnowcarver

Awesome! Thanks for the sticky Mark.

Wayne, Vatche, thank you too.

__________________

My YouTube Channel

BoostFiend510

Great thread with great info! I have one of these bad boys if anybodys interested hmu!

DreamN

No 6 speed to KA. You killed my dreams Joel. lol


Great tech thread. This is more of what Zilvia needs.

__________________
- Jimmy

Wanted:
TBD

For Sale:
TBD

srkid50

Really nice post. Had all the information I needed to hear. I am just curious..... if you have the time, you think you can research the HPI transmission? I hear that company took the NISMO tranny and made it stronger with less noise on the higher RPMs. I was reading it under RHDjapan.com.

Again, great job.

Oh, don't have a car yet but will be buying an S15 around April. Got to finish paying off debts first . Driving a freaking Honda Accord for the time being just incase anyone was wondering what car I drove.

Jacks_s13

So to put a SR20DET from a S15 into a S13 would require a S15 transmission crossmember, driveshaft, and a way to get the speedo sensor to work? and of course all the other usual stuff. I have heard you can use the stock S13 Crossmember.

FLMadness

s14 slave cyl. works on a s15 as well. figured id add that since i just found out trying it myself

bornloser_182

thanks for the goog thread

sidewaysil80

any options to tighten up the shifter? i know the hks springs arent compatible or the cusco shifter collar. are their any similiar options for the 6mt shifter? also, i noticed you said the oem clutch should be upgraded once you go above 300whp, but just how durable is it? i know thats a relative question but from what i gather you're still using it so i was just wondering for how long and what kind of driving you were doing with it?

xpertsnowcarver

I'm still not certain on the options to tighten/shorten the shifter on the 6MT. I've seen a few modified/aftermarket shifters on the Upgarage website, but there wasn't enough info in the ads for me to bother buying one.

I may have jumbled my words but generally speaking, the 6MT is going to fail due to an impulse/jerk. So, getting a clutch kit with harsh engagement, such as a hyper single, is going to significantly increase the odds of shearing teeth. This transmission can handle at least 300WHP, but if you're not smooth with your clutch engagements, completely letting off the throttle at 7500RPMS in second gear, clutch kicking like its 2012, then you're 6MT is going to fail. On full deceleration, the weakest gears are 1st-3rd, which usually fail at high RPMs. (The engine is trying to slow down while the momentum continues to drive the car forward. Bother gears become drivers, and you end up with two opposing forces that meet at the teeth in the transmission.) Clutch kicking with this much horsepower and very sticky tires will shear some teeth. Using the hand brake and powering the car through a drift should be fine. It's possible to drift, but generally its not ideal for +300WHP.

On my track car, I use the Autech (Nismo/Exedy) flywheel and a Fidanza 3:2 Clutch Kit. Been using this setup since 2009 and still have yet to replace the clutch. On my daily, I use the OEM Dual-Mass flywheel and an unsprung clutch kit (currently an OEM Nissan kit). The flywheel and clutch kit were used when I bought the swap, but I've added another 5000 miles to it and still feels great.

I use my track car for road racing. Currently, the engine is only doing 200WHP. I've fooled around with a friend's S13 with 6MT (270WHP and about 250TQ) and drifted around a few corners. Transmission felt fine. I believe he is also using the OEM Dual-Mass flywheel and an unsprung clutch kit (unsure of brand).

__________________

My YouTube Channel

Big Zee

I try not to let the blonde come through to often, but reading this thread I so far only have one question sir.

on the graphs with grey and black lines, which one is the nismo gears and which one is the factory gears?

thank you, and I apologize if I missed that part.

xpertsnowcarver

Light Grey is OEM Transmission gearing. Bold Black is the aftermarket comparison.

__________________

My YouTube Channel

HPKMotorsports3

How much to these trannys go for?

__________________

xpertsnowcarver

A bit hard to answer. Here in the state, they usually sell for $400-450 for the transmission alone. Maybe $1000 if the flywheel, clutch kit, crossmember, and driveshaft (new, steel) are included. But, I'm no one to say what they should cost. I'm just posting what I've seen them go for.

In Japan, the 6MTs still sell for about $650, but shipping is an arm/leg.

__________________

My YouTube Channel