The 6T40 and the 6T70 get lumped together because they share a name pattern, a fluid, a control philosophy and even a clutch-naming scheme. GM's own engineers say the small unit borrows the big unit's powerflow. But put the two cases on the bench and the differences show up fast: torque capacity, pump drive, solenoid count, generation changes on different years, and failure points that do not line up. Order 6T70 parts for a 6T40 (or the reverse) and nothing fits.
This guide puts the factory numbers side by side, from GM's own SAE paper, launch release, OBD tables and capacity data, with hardware and failure detail from Sonnax and ATRA's GEARS Magazine. Sources are numbered at the bottom.
Quick Answer: 6T40 vs 6T70
- Size class: The 6T40 (and the stronger 6T45) is GM's small front-drive six-speed for compact cars and small SUVs. The 6T70 (and 6T75) is the mid-size unit for V6 cars and crossovers.
- Torque: GM rates the 6T40 up to 240 Nm (177 lb-ft) of gas engine torque [1]. GM rated the 6T70 for 280 lb-ft engine torque and 462 lb-ft gearbox torque [2].
- Powerflow: The same six-speed layout on both: three simple planetaries, three brake clutches, two rotating clutches and a one-way clutch [1][3].
- Shift solenoids: The 6T40 has one on/off shift solenoid. The 6T70 has two, SS1 and SS2 [3][4].
- Fluid: DEXRON-VI in both. In the 2012 Malibu, which offered both, a drain and refill is 5.3 qt for the 6T40 and 6.3 qt for the 6T70 [6].
- Generations: The 6T40 Gen 2 change hit in 2012. The 6T70 Gen 2 change rolled in over the 2013-2014 model years [3][4]. Gen 1 and Gen 2 parts do not cross over on either unit.
Where Each Unit Came From
The 6T70 came first. GM's May 2006 release announced the 6T70 and 6T75 as new for the 2007 model year, built in Warren, Michigan, with the Saturn Aura and Pontiac G6 getting the 6T70 and the Saturn Outlook getting the 6T75 [2]. Over the next decade the 6T70 family spread across the Equinox, Malibu V6, Impala, Traverse, Acadia, Enclave and others.
The 6T40 followed for the 2008 model year. In SAE paper 2010-01-0857, GM engineers Tejinder Singh and Richard Olenzek describe the 6T40/45 as the replacement for the four-speed 4T40/45 in small cars up to small SUVs [1]. GEARS Magazine notes it first went into the 2008 Malibu, was added to the Saturn Aura in 2009, and was standard on a range of GM cars by 2010 [4]. Later it showed up in the Cruze, Sonic, Trax, Encore and the four-cylinder Equinox and Terrain. GM still lists a 6T40 (RPO MNH) in its 2026 Trax and Envista capacity charts [6].
The 2012 Malibu is a good example of how close the two units sit in the lineup. The 2.4L four-cylinder got the 6T40 (RPO MH8). The 3.6L V6 got the 6T70 (RPO MH2) [6]. Same car, same fluid, different transmissions, different parts.
Same Powerflow, Different Hardware
GM's SAE paper says outright that the 6T40/45 uses "a six-speed powerflow common with" the 6T70/75: three simple planetary gear sets, three brake clutches and two rotating clutches [1]. The clutch names carry over too. Sonnax lists the 6T70 packs as the 1-2-3-4 (forward), 2-6 (intermediate), low/reverse, and the two rotating clutches, 3-5-R and 4-5-6 [3]. If you know which clutches apply in which gear on one unit, you know it on the other.
The hardware around that powerflow is where they split:
- Packaging. The 6T40 was designed "on-axis," with most of the content on the engine axis so it packages more like a manual gearbox. It uses an output chain transfer, a planetary final drive, a one-piece case and 197 mm between the engine axis and the output axis [1]. The two rotating clutches are stacked radially to keep it short.
- Pump. The early 6T40 has an on-axis pump [1]. The 6T70 uses a remote-mounted, off-axis, chain-driven vane pump [3]. GM moved the 6T40 pump off-axis for the Gen 3 update, which GEARS covers in the 2013-2015 Malibu 2.5L and 2016 Encore 1.4L turbo [5].
- Final drives. The 6T70 family came with several final drive ratios. Sonnax lists GW5 = 3.16, F07 = 3.39, D70 = 2.77 and F71 = 2.44 [3]. GM's launch release listed 2.77 for the 6T70 and 3.16 for the 6T75 [2].
- Mass. GM listed the 6T70 at 102 kg (about 225 lb) wet [2]. The 6T40/45 came in 1-3 kg lighter than the four-speed 4T40/45 it replaced [1].
Specs Side by Side
Torque capacity
The SAE paper rates the 6T40 for up to 240 Nm with a gas engine and 280 Nm with a diesel. The 6T45 takes 315 Nm gas and 380 Nm diesel [1]. GM says the 6T40 and 6T45 use the same component radii, with the lengths changed to get the extra torque capacity [1]. GM's launch release rated the 6T70 at 280 lb-ft of engine torque (about 380 Nm) and 462 lb-ft of gearbox torque, with a maximum validated GVW of 4,850 lb. The 6T75 was rated for 6,384 lb [2].
In plain terms, a 6T70 is built for 1.5 times or more the engine torque of a 6T40. That is why a 6T40 sits behind four-cylinders and small turbos, and a 6T70 sits behind the 3.0L, 3.5L and 3.6L V6.
Gear ratios
GM's launch release lists the 6T70 at 4.48, 2.87, 1.88, 1.47, 1.00 and 0.74, with 2.88 reverse and an overall spread of 6.04:1 [2]. The SAE paper gives the 6T40 an overall spread of 6.1, with a deeper first gear and a taller top gear than the 4T40 it replaced [1]. GEARS lists it at 6.11:1 [5]. Both are direct in fifth and overdrive in sixth. The small unit runs a slightly wider spread to help the smaller engines it sits behind.
Fluid and capacity
Both use DEXRON-VI. The 2012 Malibu owner manual lists the 2.4L with the 6T40 (MH8) at 5.0 L / 5.3 qt for a drain and refill, and the 3.6L with the 6T70 (MH2) at 6.0 L / 6.3 qt [6]. GM's 2026 capacity chart lists the 6T40 in the Trax and Envista at 4.0-6.0 L (4.2-6.3 qt) for a fluid change [6]. GM's 2006 release gave the 6T70 a total fluid capacity of 9.0 L [2]. A drain and refill only replaces part of the fluid on either unit, so check the level hot, the way the owner manual says to.
Controls: One Shift Solenoid vs Two
Both units have the control module bolted inside the transmission. GM calls it the TEHCM. The 6T40 SAE paper says its controller and control system are "similar to" the 6T70/75 [1]. Both use pressure control solenoids to run each clutch regulator directly, which is what allows clutch-to-clutch shifts. But the solenoid count is different.
6T40 (seven solenoids). Per GEARS, there are six pressure control solenoids (line pressure, PCS2 for 3-5-R, PCS3 for R-1/4-5-6, PCS4 for 2-6, PCS5 for 1-2-3-4, and TCC) plus one on/off shift solenoid that drives the clutch select valve. The pressure control solenoids read 3-5 ohms and the shift solenoid reads 16-20 ohms [5].
6T70 (eight solenoids). Per Sonnax, there are two on/off shift solenoids, SS1 and SS2, plus the same six pressure control solenoids, PCS1 through PCS5 and TCC. SS1 runs clutch select valve 2. SS2 runs clutch select valve 3 and is listed as "6T70 only" [3]. The TEHCM is a Bosch 32-bit unit, and Sonnax points out the spring-loaded bracket that holds it against a heat sink on the valve body. Leave it out and the TCM shuts down from heat [3].
That extra solenoid shows up in GM's own diagnostic tables. In the 2011 OBD document covering both units, the 6T70 section has P0756 (shift solenoid B stuck off), P0976/P0977 (shift solenoid B circuit) and P1751 (shift valve 1 performance). None of those is in the 6T40 section [7]. If a scan tool shows P0756 on a 6T40, check what the vehicle really has before you order parts.
The thresholds differ even on shared codes. Both units set P0716 when input speed drops 1350 RPM or more, but the 6T40 needs that for 0.8 seconds and the 6T70 for 1.5 seconds. For P0751 (shift solenoid A stuck off), the 6T40 looks for 400 RPM of slip with 5 fail counts. The 6T70 looks for 200 RPM with 8 fail counts [7]. Diagnose each unit from its own table.
Generation Changes Hit in Different Years
Both units got a Gen 2 redesign. The changes were made in different years and the parts are not interchangeable, so the generation matters as much as the model when you order.
6T40: 2012
GEARS lists nine items GM changed in the 2012 6T40 update: valve body, valve body solenoids, TEHCM, pump, case, friction material and piston return springs in every pack, wave plates removed, and the 4-5-6 clutch drum [4]. The Gen 1 ring tower uses four sealing rings and Gen 2 uses three. The Gen 1 4-5-6 pack is four frictions and a wave plate. Gen 2 is five frictions and no wave plate [4]. Gen 1 has pressure switches and Gen 2 has none. PCS2 changed from normally high to normally low, and PCS5 from normally low to normally high [5]. To tell them apart, check the 8th digit of the TEHCM number: 1, 2 or 3 is Gen 1, and B, C or D is Gen 2 [5].
Dennis Madden's GEARS write-up shows how this goes wrong. A Gen 2 ring tower and 4-5-6 drum fitted to a Gen 1 case can pass a road test. But Gen 2 lacks the inner fluid-dam seal and the fourth ring, so the Gen 1 compensator feed regulator stays wide open. That leak can later show up as low line pressure and the transmission falling out of gear at a stop [4]. His verdict is that the swap is a non-starter.
6T70: 2013-2014
Sonnax says the 6T70 (RPO M7W/M7U) and 6T75 (M7V/M7X) got a major controls update for the 2013 model year, phased in over two years. Both Gen 1 and Gen 2 units were built in 2013-2014 [3]. Gen 2 dropped the four pressure switches and uses clutch pulse learning instead. The solenoids changed from variable bleed to variable feed, and the valve body, spacer plate, several wave plates and frictions changed too. The 1-2-3-4 pack went from seven to nine thinner plates with a notched piston, and the 3-5-R/4-5-6 housing was recast with its holes moved 30 degrees [3]. Gen 1 RPOs are MH2/MH4 (6T70) and MY9/MH6 (6T75). Sonnax states that the Gen 2 RPOs are "NOT designed to be interchanged" with Gen 1 [3].
Earlier 6T70 updates are worth knowing on a Gen 1 rebuild. Updated wave plates for the 1-2-3-4 (24259063), 2-6 (24259816), 3-5-R (24254103) and low/reverse (24259817) clutches came in for 2012 and fit earlier years. The cooler lines changed in mid-2008 because of leaks, and the new line will not fit the old case [3].
Where Each One Fails
6T40: The well-known Gen 1 failure is the ring tower and the 4-5-6 wave plate, per GEARS [4]. Gen 1 units also carry the normally closed pressure switches in the TEHCM, so a switch or switch seal problem can set codes that look like a clutch problem. On any 6T40, confirm the generation before you buy a drum, a solenoid body or a TEHCM.
6T70: Sonnax's list of 6T70 problems centers on the valve body and wave plates. A worn actuator feed limit valve can cause solenoid codes, clutch failure and wrong-gear starts. Pressure regulator wear can cause erratic line pressure, burnt clutches, low converter and lube flow, and overheating. 4-5-6 accumulator piston problems can cause a 3-4 flare, a harsh 3-4 shift and a burned 4-5-6 clutch [3]. On Gen 1 units, Sonnax lists the pressure switches as open at 8 psi and closed at 12 psi [3]. A vacuum test on the valve body is the fastest way to find a worn bore.
Can You Swap a 6T70 for a 6T40?
Not as a bolt-in. Mounts, axle geometry, final drives and calibrations are all vehicle-specific, so it becomes a platform conversion. If a 6T40 car keeps burning up its transmission, the fix is a correct rebuild with the right generation's parts.
Which One Is Better?
Neither is better. They were sized for different engines. The 6T70 has the torque capacity, the extra shift solenoid and the bigger fluid volume for V6 crossovers and towing. The 6T40 is a lighter, more compact unit for engines that make well under 240 Nm. Built with the correct generation's parts and filled with DEXRON-VI, both hold up in the vehicles they were built for. The rebuilds that come back usually have mixed generations, the wrong wave plates, a missing TEHCM heat-sink bracket, or a bore wear problem in the valve body that nobody vacuum tested.
6T40 and 6T70 parts at CoreTransmissionParts
CoreTransmissionParts carries 6T70 master rebuild kits with overhaul gaskets and a 6T40 solenoid kit. Confirm the unit and generation (RPO and the TEHCM number) before you order.
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What is the difference between a 6T40 and a 6T70?
The 6T40 is GM's small front-drive six-speed for four-cylinder cars and small SUVs, rated up to 240 Nm of gas engine torque. The 6T70 is the mid-size unit for V6 vehicles, rated at 280 lb-ft engine torque. They share the same powerflow and clutch names, but the 6T70 has two shift solenoids instead of one, a different pump drive and different parts.
Are 6T40 and 6T70 parts interchangeable?
No. The clutch names and powerflow are the same, but the cases, drums, valve bodies, solenoid bodies and TEHCMs are specific to each unit. Each unit also has its own Gen 1 and Gen 2 parts that do not cross over.
How do I tell a Gen 1 from a Gen 2 6T40 or 6T70?
On a 6T40, check the 8th digit of the TEHCM number: 1, 2 or 3 is Gen 1, and B, C or D is Gen 2. The change came in 2012. On a 6T70, check the RPO: MH2 and MH4 are Gen 1, M7W and M7U are Gen 2. Gen 2 was phased in over 2013 and 2014.
How much fluid does a 6T40 and a 6T70 take?
Both use DEXRON-VI. In the 2012 Malibu, a drain and refill is 5.0 L (5.3 qt) for the 6T40 and 6.0 L (6.3 qt) for the 6T70. GM lists the 6T70 total capacity at 9.0 L. Check the level hot after any service.
Can I put a 6T70 in place of a 6T40?
Not as a bolt-in. The mounts, axles, final drive and control calibration are specific to the vehicle, so it becomes a platform conversion. If a 6T40 keeps failing, rebuild it with the correct generation's parts.
Sources
- Singh, T. and Olenzek, R. (General Motors), "General Motors Small Front Wheel Drive Six speed Automatic Transmission Family," SAE Technical Paper 2010-01-0857, SAE 2010 World Congress. Backs the 2008 MY launch, the 4T40/45 replacement, the 240/280 Nm (6T40) and 315/380 Nm (6T45) ratings, the 6.1 ratio spread, the powerflow shared with the 6T70/75, the on-axis pump and layout, the output chain transfer, the 197 mm center distance, the 1-3 kg mass saving and the controller similar to the 6T70/75. sae.org
- General Motors Powertrain, "GM Launches More Fuel-Saving Six-Speed Automatic Transmissions" (press release, May 18, 2006). Backs the 2007 MY 6T70/6T75 launch, the Warren, Mich. assembly, the Aura/G6/Outlook applications, the 280 lb-ft engine and 462 lb-ft gearbox torque, the 4.48/2.87/1.88/1.47/1.00/0.74 and 2.88 reverse ratios, the 6.04 spread, the 2.77 and 3.16 final drives, the 102 kg wet weight, the 9.0 L capacity and the 4,850/6,384 lb GVW. release text
- Sonnax, "6T70/6F50 Webinar" (technical presentation). Backs the 6T70 clutch names, the off-axis chain-driven vane pump, the SS1/SS2 (SS2 6T70 only) and six-PCS solenoid table, the Bosch TEHCM and heat-sink bracket, the Gen 1 pressure switches (8/12 psi), the RPO and final drive codes, the 2012 wave plate part numbers, the mid-2008 cooler line change, the 2013-2014 Gen 2 change list, and the AFL valve, pressure regulator and 4-5-6 accumulator symptoms. PDF
- ATRA GEARS Magazine, Dennis Madden, "It Worked on the Road Test! The 6T40 4-5-6 Drum Interchange Quandary" (July 2018). Backs the 2008 Malibu / 2009 Aura introduction, the nine 2012 Gen 2 changes, the four vs three ring tower seals, the 4-5-6 pack make-up, the Gen 1 ring tower and wave plate failure, and the low-line-pressure result of a mixed Gen 1/Gen 2 drum swap. gearsmagazine.com
- ATRA GEARS Magazine, Jarad Warren, "Understanding GM 6T40 Solenoids" (June 2017) and Mike Brown, "Generation Gap: 6T40 Gen v3" (July 2019). Backs the 6T40 solenoid list, states and resistances, the TEHCM 8th-digit generation ID, the Gen 2 pressure switch deletion, the 6.11:1 spread, the Gen 3 off-axis pump and the DEXRON-VI fill. solenoids, Gen 3
- General Motors, 2012 Chevrolet Malibu Owner Manual (Capacities and Specifications, p. 12-3) and GM TechLink "2026 Transmission Capacities & Fluids." Backs the MH8 (6T40) 5.0 L/5.3 qt and MH2 (6T70) 6.0 L/6.3 qt drain-and-refill figures, DEXRON-VI, and the 2026 Trax/Envista 6T40 (MNH) 4.0-6.0 L capacity. owner manual, TechLink
- General Motors, 2011 OBD II Diagnostic Tables, "11OBDG08 TRANS Diagnostics" (6T40 and 6T70 Unique Sections). Backs the code lists (P0756, P0976/P0977 and P1751 in the 6T70 section only), the P0716 limits (1350 RPM, 0.8 s on the 6T40, PDF p. 46; 1.5 s on the 6T70, PDF p. 154) and the P0751 limits (400 RPM / 5 counts on the 6T40, PDF p. 59; 200 RPM / 8 counts on the 6T70, PDF p. 167). gm.com PDF
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