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[Datsun 1200 encyclopedia]


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Categories: Transmission Modifications | Transmission

6-speed transmission gives you two (count 'em 2) overdrive gears. Or some have a close ratio direct-5th with overdrive, which is better for performance. 6-speeds can be modified to fit Datsun 1200. Just cut the bellhousing and weld on a fragment of A-series bell housing, then machine the input shaft smaller.


Aisin AZ6

6-speed with A-series bell grafted on
19983.jpgAlbum 19983

R30A  81-series gearset 285 Nm
R31A  85-series gearset 450 Nm

The basic Aisin AZ6 gearbox was made in several versions, with front cases for these engines:

  • Nissan FS6R30A (source: Nissan pickup 2004-)
  • Nissan FS6R31A for SR20DET (source: S15)
  • Nissan FS6R31A for VQ35 (source: Z33 "350Z")
  • Nissan FS6R92A for VQ35 (source: G35) 130 lbs weight
  • Nissan FS6R92A for SR20 (source: S15)
  • Mazda Renesys (RX8 rotary)
  • Mazda Y16M-D F & B (1999-2005 MX-5)
  • Toyota J160 for 1G & 3S (E10 Toyota Altezza/Lexus IS200)
  • Toyota 86/Scion FR-S
  • Subaru BRZ


A limited run was produced of custom front cases for Toyota T-50 bellhousing, so with this gearbox a Dellow kit might work to mate it to the A-series engine.

But other wise, use the Cut-n-Shut method.


Nissan sells brand-new 350Z 6-speeds for $1700-$2000 (MSRP of $2300, so shop around. Your local Nissan dealer may charge the full price, but other dealers are selling for under $1800 as of June 2022).

Nissan RWD six-speed is plentiful in wrecking yards and inexpensive new ($1800) or used ($900). Use an adapter plate and bob's your uncle. Reportedly 3x stronger than an SR20DET 5-speed. It is a true direct-fifth gearbox + overdrive.

  • Z33 "350Z" 2003-
  • 2005- six-cylinder Frontier, Xterra, Pathfinder

7054.jpgAlbum 7054

FS6R31A    F5C56A
1st 3.794  3.757
2nd 2.324  2.374
3rd 1.624  1.659
4th 1.271  1.291
5th 1.000  1.000
6th 0.794  --
Rev 3.446  4.046

S15 6-speed

The 1999-2002 Nissan Silvia S15 Strawberry with SR20DE/SR20DET had an optional close-ratio 5-speed + overdrive (6 forward speeds total). In AUS, the six-speed was in the Nissan 200SX Spec-R model.

S15 modified; A-series bell grafted on
19983.jpgAlbum 19983

  • FS6R92A
  • only 16kg heavier than a standard 1200 4spd
  • Close ratio 1-5, with overdrive 6th. It is perhaps the best ratios for an A-series engine

Gear Ratio

Comparison with A-series 5-speeds

.model. First. Second Third. Fourth Fifth. Sixth. Reverse
FS6R92A 3.6264 2.2000 1.5412 1.2132 1.0000 0.7674
F5C56A. 3.757. 2.374. 1.659. 1.254. 1.0000 ------ 4.04 
F5C56Ac 2.676. 1.691. 1.398. 1.181. 1.0000 ------ 2.877
FS5W60L 3.513. 2.170. 1.378. 1.0000 0.846. ------ 3.764
FS5W63A 3.382. 2.013. 1.312. 1.0000 0.854. ------ 3.57

Comparison with S14 5-speed

.model. First. Second Third. Fourth Fifth. Sixth. Reverse
FS6R92A 3.6264 2.2000 1.5412 1.2132 1.0000 0.7674

Comparision of various Aisin AZ6 models:

FS6R92A First. Second Third. Fourth Fifth Sixth. 
Silvia. 3.6264 2.2000 1.5412 1.2132 1.000 0.7674
RX8.... 3.760. 2.269. 1.645. 1.187. 1.000 0.843. 
MX5 99. 3.760. 2.269. 1.645. 1.257. 1.000 0.843.
RS200.. 3.874. 2.175. 1.484. 1.223. 1.000 0.869.

Pilot Bushing

S15 5-speed FS6R92A

  • used on L, Z, VG, VQ, SR, KA, and CD engines (same as 71C bushing)
  • Pilot Bushing Inside Diameter: 0.626 to .6300 inch (Length: .689")
  • Pilot Bushing Outside Diameter: .814 to .815"

Since this is much larger in diameter than the A-series, machining is needed.

A-series crankshaft bore is for a bushing with 0.671" O.D., length .723"

  • The FS6R92A input shaft end can be turned down to ~.671 O.D.
  • Could the A-series crank pilot hole be bored out to .814" so the 71-Series bush can be fitted?

Input shaft end turned down to smaller diameter

Clutch Disc

FS6R92A clutch disc [all 240mm]

  • 30100-85F00 9901-0011
  • 30100-85F14 0011-
  • Spline O.D.: 1'
  • Spline: 24 teeth

There is an A-series clutch disc that is 1' x 24T: 30100-K0500.

Input Shaft Length

How far does the FS6R92A input shaft extend past the transmission face?

  • 5-speed: about 17mm past the flange
  • 6-speed: about 10mm inside the flange


S15 6-speed does not have a speedometer gear.

Clutch Release

How to connect up the clutch?

Gearshift Location

Comparision of Nissan 6-speed with long-5-speed and short 4-speed. The location of the shifter is close to the location of stumpy gearbox shifter.

top.jpg side.jpg

Rear Crossmember

Use a generic crossmember to fit a 6-speed.

See Main Article: Wide gearbox crossmember

Propeller Shaft

The 6-speed overall length is greater than a stumpy gearbox, but not as long as a a longtail Nissan transmission.

6-speed vs 71C long vs 71B long vs F4W63 stumpy

Toyota J160

A limited run was produced of custom front cases for Toyota T-50 bellhousing, so with this gearbox a Dellow kit might work to mate it to the A-series engine.

Aisin AZ6 with custom front case for T-50 removable bell housing. A custom input shaft is used.

Toyota J160 dimensions

overall length: 740mm (not counting shifter)
* including shifter: 870mm
length front case: 270mm
length gear case: 190mm
length tail housing: 28mm 

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