E30 325i manual swap to 6-speed GS6-37DZ

A typical E30 325i automatic transmission swap to manual with the Getrag 260

A typical manual transmission swap uses the 5-speed Getrag 260 transmission from a manual E30.
Here is the list of the parts that are required for a swap:

  • Transmission input shaft seal
  • Engine rear main seal
  • Transmission
  • Transmission oil
  • Transmission crossmember 23711176574
  • Transmission mounts 23711175939 x2
  • Transmission mount nuts 07119905515 x4
  • Washer 33311108205 x2
  • Washer 07119904115 x2
  • Shifter assembly
  • Selector rod | Shift link w/washers and clips
  • Shift handle
  • Shift knob and emblem
  • Nylon cup and bushing
  • Shift lever insulating rubber boot
  • Shift lever leather boot
  • Lock pin for support arm
  • Bushing mounting nut
  • Transmission to block bolts (set, you can reuse the bolts that came off your auto)
  • Giubo bolts
  • Giubo
  • Manual driveshaft
  • Center bearing assembly
  • Reverse light switch
  • M/T reverse lamps wiring harness BMW 23141220263
  • Clutch cruise control switch and wiring
  • Flywheel
  • Flywheel spacer plate
  • Flywheel bolts x8 (need new)
  • Throwout bearing
  • Clutch/Pressure Plate assembly
  • Clutch fork
  • Clutch fork bearing
  • Clutch master cylinder
  • Clutch master fluid line connector
  • Clutch slave cylinder
  • Clutch hardline
  • Firewall grommet
  • Clutch soft line
  • Brake pedal 35211154729
  • Clutch pedal 35311156838
  • Clutch and brake pedal rubber pads 35211108634
  • Hex bolt for the pedals M10x175 07119912721

The most expensive parts are the Getrag 260, manual driveshaft, shifter and selector rod, flywheel, and clutch. It’s very difficult to find a Getrag 260 that doesn’t need a rebuild. BMW sells a refurbished one for $3,500.

If you have to change so many parts, isn’t it better to install a newer 6-speed transmission with its driveshaft, shifter, clutch, differential, and linking parts?

GS6-37DZ transmission

A newer one can be the European diesel transmission GS6-37DZ. This swap was pioneered by Wanganstyle.

This article describes only the Project Research stage. I’m trying to collect as much information as possible. I don’t know what will work and what won’t.

The GS6-37 is a 6-speed manual transmission manufactured by ZF Friedrichshafen AG and Getrag. It is designed for longitudinal engine applications and is rated to handle up to 370 newton metres (273 lbf⋅ft) of torque.

Gear ratios

Gear ratios for Getrag 260
1 2 3 4 5 R
3.83 2.20 1.40 1.00 0.81 3.71
Gear ratios for diesel GS6-37DZ
1 2 3 4 5 6 R
5.14 2.83 1.79 1.26 1.00 0.83 4.64
Gear ratios for gasoline GS6-37BZ
1 2 3 4 5 6 R
4.350 2.496 1.665 1.234 1.000 0.851 3.926

Differential

Which differential ratio is the best?

  • The acceleration in the 2, 3, 4 gears should be similar to the Getrag 260 + a 4.10 or 3.73 differential.
  • The 6th gear should be good for low-RPM freeway cruising.
  • The 1st gear should be usable.

The Getrag 260 with a 4.10 differential compared to the GS6-37DZ with a 3.15 differential:

Differential ratios 4.1 3.15

The Getrag 260 with a 3.73 differential compared to the GS6-37DZ with a 3.07 differential:

Differential ratios 3.73 3.07

It’s possible to find Z3 3.07 and 3.15 medium 188mm differentials. They have Torsen LSDs and require little maintenance for regular driving. They are more modern and have few miles as the regular Z3 was a weekend car. The Z3M had a 3.23 clutch-type LSD differential.

Getrag 260 and GS6-37DZ bellhousing comparison

Looking at the different variants of the GS6-37DZ transmission, only the earlier variants GS6-37DZ — THES (23007562730) and GS6-37DZ — TJEM (23007565194) can be used.

The main advantage of the GS6-37DZ (D – diesel) over its sibling GS6-37BZ (B – benzin, petrol, gasoline) is the slant(tilt) degree of 20°. The slant degree of the M20 engine in the 325i is the same. The engine doesn’t stand vertically to save on the height. The GS6-37BZ has the slant degree of 30°.

Getrag 260 and GS6-37DZ bellhousing comparison

As you can see, the GS6-37DZ has more bellhousing holes than the Getrag 260: 2 at the bottom and 1 pin at the top.

The transmission will be mated with the BMW M20 engine. The top pin interferes with the starter. But the M20 starter won’t probably work with the GS6-37DZ flywheel, so it’ll be replaced anyway.

BMW M20 engine rear

The bottom part of the M20 engine can be disconnected. It’s called the Bowl reinforcement (11141286342). An additional hole can be drilled and tapped in it, but there is no casting for it in the back of the reinforcement. Maybe, a nut can be used.

bowl_reinforcement

Transmission drive shaft differences

The driveshaft in the Getrag 260 has 10 splines, the driveshaft of the GS6-37DZ has 22 splines. So, a clutch disk should have 22 splines too.
The driveshaft in the Getrag 260 is longer and its pilot bearing is inserted into the crankshaft of the engine.
The driveshaft in the GS6-37DZ is shorter and its pilot bearing is in the flywheel.

Rear transmission mount brace (cross member)

The GS6-37DZ is mounted differently. The top (22316760303) E90 Transmission supporting bracket is available. Then, the mounting style and dimensions should be similar to the 6-speed Getrag 420G, for which some companies create braces.

GS6-37DZ rear mounting brace

The transmission cross member can be sourced from Bayside Fabrication.
Bayside Fabrication crossmember

Available crossmember products

Reboot Engineering E36 GS6-37 6 Speed Conversion Transmission Bracket.

This part is used when converting an E36 to a 6 speed when using a ZF GS6-37 transmission that is commonly found in an E46 330. This adapter raises the rear trans mount 30mm and eliminates the need to run spacers with a E36 auto cross-member. Components are constructed of 6061 Aluminum.

E36 GS6-37 6 Speed Conversion Transmission Bracket

Zionsville BMW E36 6 Speed Conversion Transmission Mounting Bracket.

Kassel Performance BMW E30 Swap Custom Transmission Mounting Kit.

Drive Shaft

The GS6-37DZ is 635 mm long. It is 120 mm longer than the Getrag 260. The automatic transmission ZF HP4-22 is 685 mm long.
As the length of the manual transmission Getrag 260 drive shaft for the E30 is 1,489 mm, then the length of the drive shaft for the GS6-37DZ must be close to 1,370 mm.

gs6-37bz dimensions

The E36 M3 automatic drive shaft (26112228212) should be compatible with its length of 1,346 mm. It’s about 25 mm short.

M3 auto drive shaft 26112228212

Also, the European E36 automatic drive shaft (26111227441) should be compatible too with its length of 1345 mm.

It seems that many 4-bolt E36 drive shafts have the same rear half. It’s only the front half that has different lengths. Both u-joints are located in the rear half, and they wear out. The front half is just a pipe with connectors.

The manual Z4 front part(26117514468) can be used with the rear E36 part.

The giubo (26112226527) is 96mm in diameter, 35 mm wide, and it is connected using M12 bolts.

The drive shaft center support mount must be from the E30 (26121226723). Probably, it should be mounted backwards.

Shifter

The shifter carrier and selector rod for this conversion must be custom.

Shifter carrier and Selector rod

Reboot Engineering http://rebooteng.com/parts/e36-gs6-37-6-speed-conversion-shifter-carrier/.

This part is used when converting an E36 to a 6 speed when using a ZF GS6-37 transmission that is commonly found in an E46 330. The part is necessary for the conversion to ensure that the shifter correctly aligns with the hole in the transmission tunnel. This part only works with 6 cylinder cars. This kit requires front carrier bushings (BMW Part Number 25117519670). The machined components are constructed of 6061 Aluminum.

Includes
1- Aluminum Carrier
1- 304 Stainless selector rod

Reboot Engineering shifter carrier

Adam from Reboot Engineering:

the shift carrier works in an E30 and we have also sold the trans bracket to a few customers with E30’s. I believe they also use the E36 auto crossmember but cant
confirm that 100%. You also should not need any risers after its installed.

The selector rod is straight, won’t it interfere with the giubo?

Zionsville BMW E36 6 Speed Conversion Shift Arm Support Bracket.
Zionsville shifter carrier

A longer shifter carrier can be shortened and welded.
gs6-37 Shifting carrier welded

Flywheel and Clutch

The flywheel and clutch are from the E46 330i: the twin-mass flywheel(21207533868) and the clutch(21207531556).

The LuK DMF053 twin-mass flywheel.
LuK DMF053 twin-mass flywheel

The original M20 flywheel.
M20 flywheel

The LuK 6243575000 clutch kit.
LuK 6243575000 clutch kit

Clutch Slave Cylinder

The master clutch cylinder is from the E30. The slave clutch cylinder is from the E36 325i(21521159045). There should be other compatible clutch cylinders.

Starter

The starter from the E46(12412354693) is compatible with the E46 flywheel.

The Bosch SR0448N from the E46 has the threaded holes for the bolts, no E30-style nuts will be needed.

The E30 starter(12411726504) specifications:
Rated Power [kW]: 1,4
Voltage [V]: 12
Number of Teeth: 9
Rotation Direction: Clockwise rotation
Number of mounting bores: 2
Flange Ø [mm]: 76
Number of Thread Bores 0
Plug Type ID: M6
Clamp: M8
Length 3 [mm]: 25
Length [mm]: 184.21

The E46 starter(12412354693) specifications:
Rated Power [kW]: 1,4
Voltage [V]: 12
Number of Teeth: 9
Rotation Direction: Clockwise rotation
Number of mounting bores: 3
Flange Ø [mm]: 76
Number of Thread Bores: 2
Plug Type ID: M6
Clamp: M8
Length 3 [mm]: 23
Length [mm]: 173.21

Reverse Switch

The E30 reverse switch(23141354071) has a correct connector.

Lube and Oil

The transmission splines must be lubed.

Rebuilding the GS6-37DZ transmission

The transmission bellhousing can be opened using this crude technology.
It seems that the bellhousings of the GS6-37DZ and GS6-37BZ can be exchanged to get the gasoline engine gear ratios.

gs6-37bz bellhousing open

In addition to the new seals and new bolts, these bearings are required for a rebuild:

  • 2 bearings for the input and main shafts NSK 35TM10-A-1CG28U01 35x80x20mm
  • 1 bearing for the lay shaft SKF BA2B 633910 C(23111224808) 29.8x67x31mm
  • 1 bearing INA 712 0613 10 (INA F-223773) 27x44x23.2mm

gs6-37bz rebuild

Schematics of the GS6-37DZ

gs6-37dz schematics

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