The GM 6T70 and 6T75 are six-speed front-wheel-drive automatic transmissions that GM has used in a massive number of vehicles since 2007. The Chevrolet Traverse, GMC Acadia, Buick Enclave, Saturn Outlook, Chevrolet Malibu, Chevrolet Equinox, GMC Terrain, Buick LaCrosse, and Cadillac SRX all use some version of this transmission. The 6T70 is the lower-torque variant and the 6T75 is rated for higher-torque applications, but internally they are very similar. If you work on GM vehicles, you will encounter these units frequently.
The 6T70/6T75 is a chain-driven transmission, which is unusual for a passenger car automatic. Instead of a traditional gear train, the 6T70 uses a drive chain to transfer power from the input to the gear sets. This design choice gives the transmission a compact packaging envelope for FWD applications but introduces a wear component that conventional transmissions do not have. The chain, the wave plates, and the valve body are the three areas where problems concentrate.
For more GM and Chevy transmission resources, visit our GM hub page and Chevy hub page.
Problem 1: Drive Chain Wear and Stretch
What Happens
The drive chain in the 6T70/6T75 transfers torque between the converter housing and the gear sets. Over time, the chain stretches. A stretched chain changes the timing relationship between the input and output sprockets, which affects shift quality and can cause codes related to gear ratio errors. The chain also generates noise when worn -- a whining or droning sound that increases with vehicle speed and is present in all gears.
Symptoms
Whining noise from the transmission area that is proportional to vehicle speed. The noise is present in all gears and does not change with shifts. Gear ratio error codes -- the TCM detects that the actual gear ratio does not match the commanded ratio because the chain stretch has changed the effective ratio. In advanced cases, the chain can skip on the sprockets, which causes a sudden and alarming bang or jerk.
Diagnostic Steps
Chain wear is best confirmed with the pan off. There is a chain deflection specification -- with the pan removed, push on the chain at the midpoint between the sprockets and measure the deflection. If the deflection exceeds the service specification, the chain needs replacement. On high-mileage units (over 150,000 miles), chain wear is almost guaranteed regardless of maintenance history.
What to Do
Chain replacement on the 6T70/6T75 is an internal repair that requires transmission removal. The chain, sprockets, and chain tensioner should all be replaced together. The sprocket surfaces wear along with the chain, and installing a new chain on worn sprockets accelerates the wear rate. Most shops replace the chain assembly as part of any rebuild.
Problem 2: 3-5-Reverse Wave Plate Failure
What Happens
The 3-5-reverse clutch assembly in the 6T70/6T75 uses a wave plate (also called a Belleville spring or apply plate) to provide the clamping force for the clutch pack. The wave plate is a stamped steel disc that flexes to apply pressure. On the 6T70/6T75, this wave plate is prone to fracturing, especially on higher-mileage units and vehicles that are driven aggressively. When the wave plate fractures, the 3-5-reverse clutch loses apply force.
Symptoms
Loss of third gear and fifth gear. The transmission shifts from second directly to fourth, skipping third. Fifth gear may be absent or may engage and then immediately slip. Reverse may be weak or absent entirely. The check engine light is on with codes for 3rd gear ratio error or 5th gear ratio error. This is one of the most common internal failures on the 6T70/6T75.
What to Do
This is a rebuild-level repair. The wave plate, clutch pack, and apply piston all need to be inspected and replaced. Sonnax makes an upgraded wave plate kit that addresses the OEM design weakness. This should be standard practice on any 6T70/6T75 rebuild -- the stock wave plate is a known failure item and there is no reason to reinstall one during a rebuild.
Snap Ring Pliers Set (Internal and External)
The 6T70/6T75 uses snap rings extensively throughout the clutch pack assemblies and chain housing. A quality set of internal and external snap ring pliers in multiple sizes is essential for any work inside this transmission. Cheap snap ring pliers flex under load and launch rings across the shop.
Check Price on AmazonProblem 3: Valve Body Wear and Solenoid Issues
What Happens
The 6T70/6T75 valve body contains multiple pressure control solenoids and spool valves that manage shift timing, pressure, and converter lockup. The valve body bores wear over time, and the solenoids degrade from heat cycling and fluid contamination. The most common valve body issue is the pressure regulator valve bore wearing out, which causes erratic line pressure and unpredictable shift quality.
Symptoms
Harsh or erratic shifts that vary from one shift event to the next. The 1-2 shift may be smooth one time and harsh the next. Delayed engagement from park to drive. TCC shudder at lockup speeds. Multiple solenoid performance codes stored in the TCM. In some cases, the transmission goes into limp mode (third gear only) due to the TCM detecting inconsistent pressure responses from the solenoids.
What to Do
Valve body repair on the 6T70/6T75 is viable. Sonnax produces bore repair kits for the most commonly worn valve bores, including the pressure regulator valve bore and the TCC regulator valve bore. These kits include oversized valves and sleeves that restore the bore to specification. For shops doing 6T70/6T75 work regularly, stocking Sonnax valve body repair kits is a good investment.
If the valve body damage is extensive, a remanufactured valve body is a better option than trying to repair multiple worn bores. Remanufactured valve bodies from reputable suppliers come with new solenoids and reconditioned bores, and they carry a warranty.
Problem 4: Torque Converter Clutch Issues
What Happens
The torque converter on the 6T70/6T75 uses a multi-plate lockup clutch that is prone to shudder when the fluid is degraded or when the clutch material has worn. The GM Lambda platform vehicles (Traverse, Acadia, Enclave) are particularly susceptible because they are heavy vehicles that spend a lot of time at highway speeds with the converter locked -- the lockup clutch sees sustained load for extended periods.
Symptoms
Shudder at 40 to 60 mph at light throttle. The vehicle feels like it is driving over rumble strips. The shudder may come and go, and it is often worse when the transmission is cold. P0741 (TCC Performance or Stuck Off) may be stored. Fluid that is dark or has a burned odor indicates converter clutch material degradation.
What to Do
Start with a fluid service using Dexron VI. The 6T70/6T75 uses Dexron VI -- not Dexron III, not Mercon, not universal ATF. Fresh Dexron VI with proper friction modifier chemistry resolves TCC shudder in approximately 60 percent of cases where the shudder is the only symptom and the fluid was overdue for service. If a fluid change does not resolve the shudder within 500 miles, the converter needs replacement. A new converter is typically installed as part of any 6T70/6T75 rebuild.
ACDelco Dexron VI ATF (Case of 12)
The correct fluid for all 6T70/6T75 applications. The 6T70 has a fluid capacity of approximately 9.5 quarts total, so you need a full case for a complete drain and fill cycle. Keep cases in stock if you work on GM FWD vehicles -- you will use it constantly.
Check Price on AmazonFluid Service Procedure
The 6T70/6T75 does not have a traditional dipstick on most applications. Fluid level is checked through a level check plug on the side of the transmission case with the fluid at a specific temperature. This is a common source of problems -- shops overfill or underfill the transmission because they do not follow the correct level check procedure.
Correct Procedure
- Warm the transmission to operating temperature -- 185 to 195 degrees F, monitored with a scan tool reading the TFT sensor.
- With the engine running and the transmission in park, remove the level check plug on the side of the transmission case.
- Fluid should drip slowly from the check plug hole. If fluid flows freely, the level is too high. If no fluid comes out, the level is too low.
- Add or drain fluid as needed to achieve the correct level at the specified temperature. The level check is temperature-dependent -- checking at the wrong temperature gives a false reading.
The drain plug is on the bottom of the transmission pan. Drain capacity is approximately 6 to 7 quarts. The internal filter is accessible with pan removal and should be replaced at every other fluid service or at any rebuild. The total fluid capacity is approximately 9.5 quarts, so a single drain and fill exchanges roughly two-thirds of the fluid. For a more complete exchange, two drain and fill cycles with driving in between is the standard approach.
6T70/6T75 Transmission Filter Kit
Includes the internal filter, pan gasket, and hardware for a complete 6T70/6T75 filter service. Replace the filter at every other fluid service or any time the pan is removed for inspection or repair work.
Check Price on AmazonRebuild Considerations
The 6T70/6T75 is a complex transmission to rebuild compared to older GM units like the 4L60E or 4L80E. The chain drive, the multiple clutch packs, and the electronic controls all add complexity. A 6T70/6T75 rebuild typically runs $2,800 to $4,500 depending on what is found inside and the labor rate in the market. The chain, sprockets, and tensioner should be replaced on any rebuild regardless of their apparent condition -- they are wear items and the labor to access them is already included in the rebuild labor.
The Sonnax upgrades for the 3-5-reverse wave plate and the valve body bore repairs should be standard on every 6T70/6T75 rebuild. These are known weak points with known aftermarket solutions. Installing stock components in a rebuild when upgraded parts are available is doing the customer a disservice.
Bench Stock Jumpstart Pack — $37
The 6T70/6T75 has a lot of small components that need to be tracked during a rebuild. The Bench Stock system keeps your parts inventory organized and your warranty documentation clean.
Get the Pack →