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.
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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. GM took the failure seriously enough to issue Special Coverage bulletin 14404A, extending warranty to 10 years or 120,000 miles specifically for a "cracked or fractured wave plate, resulting in a loss of 3rd, 5th and reverse gears" on many 2007-2009 6T70/6T75 vehicles [1]. On an affected VIN, check GM's warranty system for eligibility before you quote the job.
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 3-5-R Drum Saver kit that replaces the failure-prone factory geometry to prevent comebacks on these units [2]. 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.
Problem 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. The bore to check first on a Gen. 1 unit is the AFL/solenoid pressure regulator. Sonnax explains the mechanism: the OE valve has a large reaction area and is heavily side-loaded, so it wears its bore, and as the bore wears the oil pressure feeding the shift solenoids drops. The result is solenoid performance codes, wrong-gear starts, low line pressure and eventually clutch failure [5]. That is why a unit throwing several solenoid codes at once often has nothing wrong with the solenoids themselves.
The Sonnax 124740-32K kit for Gen. 1 6T70/6T75 (it also fits the Ford 6F50/6F55) is a drop-in fix: a wear-resistant billet sleeve that seals the worn bore and gives the new valve an unworn bore to ride in, plus a .062" drill bit for rerouting balance oil at the separator plate [5]. Sonnax also offers oversized main pressure regulator valve kits for Gen. 1 and Gen. 2 valve bodies. For shops doing 6T70/6T75 work regularly, stocking these 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 -- which GM confirms in its published transmission capacities and fluids reference [3]. Fresh Dexron VI restores the friction modifier package the converter clutch depends on, and when shudder is the only symptom and the fluid is overdue, a fluid exchange is the cheap first step. In my experience it fixes a good share of these, but not most of the high-mileage ones. If a fluid change does not resolve the shudder within a few hundred miles, the converter needs replacement. A new converter is typically installed as part of any 6T70/6T75 rebuild.
Fluid Service Procedure
The 6T70/6T75 takes DEXRON VI, and the level check is temperature-dependent. This is a common source of problems -- shops overfill or underfill the unit because they read the level cold. ATRA's 6T70 product-issues seminar gives the procedure [6]:
Correct Procedure
- Park level with the parking brake applied.
- Start the engine and move the gear selector through the ranges, then idle for one minute.
- Confirm TFT is 180 to 200 degrees F on the scan tool. Driving in 2nd helps bring it up to temperature.
- Read the level on the dipstick, and if the fluid was changed, reset the transmission oil life monitor.
Per GM service information for the 6T70/6T75 [7], a fluid change through the drain plug takes approximately 4.0-6.0 L (4.2-6.3 qt), removing the valve body cover takes 5.0-7.0 L (5.3-7.4 qt), and an overhaul takes 7.0-9.0 L (7.4-9.5 qt). A single drain and fill therefore exchanges only a little more than half the fluid; two drain and fill cycles with driving in between is the standard approach for a more complete exchange. The filter is not a maintenance item on this unit: ATRA lists it as non-serviceable, replaced only after an internal repair because it sits inside the case, and gives a fluid-only service at 100,000 miles for regular service and 50,000 miles for severe service. GM's owner's manual for the 6T75-equipped Traverse lists no fluid change on the normal schedule through 150,000 miles and three on the severe schedule [8]. For a full breakdown of the three service types and what each costs, see our 6T70 fluid change cost guide.
Towing and Heat: 6T70 vs 6T75
Before you sign off on a towing customer, confirm which unit is in the vehicle. ATRA's 6T70 introduction course lists the 6T70 at a 1,000 lb (454 kg) towing rating and 280 lb-ft maximum engine torque, and the 6T75 at 4,500 lb (2,041 kg) and 299 lb-ft. The 6T75's extra capacity comes from hard parts, a shot-peened output carrier, a 5-pinion carrier, a wider transfer gear, a heavier differential carrier and a heavier ribbed case, so no cooler turns a 6T70 into a tow unit [9]. The same course describes the family as built with reduced sump volumes and reduced cooling capacity, and warns against 3rd-gear starts while towing because they can overheat the transmission [9]. It also notes the studded side cover bolts must be re-torqued whenever the cooler lines are removed, and that the TEHCM bracket that holds the module against the valve body heat sink must be installed or the TCM will go into thermal shutdown [9]. Our 6T70 towing upgrades and cooling guide covers the V92 trailering package, auxiliary coolers and severe-service intervals in detail.
Rebuild 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.
Sources
- NHTSA / General Motors — Special Coverage Adjustment Bulletin 14404A, "Transmission Clutch Wave Plate," 10 years / 120,000 miles coverage for cracked or fractured wave plate causing loss of 3rd/5th/reverse on 6T70/6T75 vehicles. static.nhtsa.gov
- Sonnax — "GM 6T40 & 6T70 Drum Saver Kits: Protection Against 3-5-R Failures & Comebacks," the upgraded replacement for the failure-prone factory 3-5-R waved plate. sonnax.com
- GM TechLink — Transmission Capacities & Fluids reference (2025 model year). Confirms DEXRON VI as the fluid for GM's current front-drive six-, eight- and nine-speed transaxles and gives their fill volumes; the 6T70/6T75-specific capacities are in source 7. gm-techlink.com
- GEARS Magazine (ATRA) — "6T40/45 Diagnosis and Fixes," family diagnostic procedure covering solenoid functional testing, sensor locations, and fluid-level temperature windows shared with the 6T70/6T75. gearsmagazine.com
- Sonnax — AFL/Solenoid Pressure Regulator Valve Kit 124740-32K, product and tech page. Backs the mechanism of AFL/solenoid pressure regulator bore wear in Gen. 1 6T70/6T75 units (large reaction area, side-loading), the resulting low solenoid feed pressure, solenoid performance codes, wrong-gear starts, low line pressure and clutch failure, the 6F50/6F55 and Gen. 1 6T70/6T75 applications, and the kit contents (billet sleeve, valve, .062" drill bit for separator plate balance oil reroute). sonnax.com
- ATRA — "6T70 Product Issues and Updates," Steve Garrett. Backs the fluid level check procedure (level surface, parking brake, idle one minute, TFT 180-200 degrees F, read dipstick), resetting the transmission oil life monitor, the non-serviceable internal filter, and the 100,000-mile regular and 50,000-mile severe fluid-only service intervals. atracom.blob.core.windows.net
- General Motors service information — "Fluid Capacity Specifications," Automatic Transmission 6T70/6T75 (2011 Saab 9-4X workshop information). Backs the 4.0-6.0 L drain plug, 5.0-7.0 L valve body cover removal and 7.0-9.0 L overhaul capacities. saabwisonline.com
- General Motors — 2017 Chevrolet Traverse Owner's Manual. Backs DEXRON VI as the specified fluid and the Normal versus Severe maintenance schedule transmission fluid change entries. chevrolet.ca
- ATRA — "6T70 Introduction" technical course. Backs the 6T70 (1,000 lb, 280 lb-ft) and 6T75 (4,500 lb, 299 lb-ft) towing ratings, the 6T75 heavy-duty hard parts, the reduced sump volume and cooling capacity design notes, the warning against 3rd-gear starts when towing, the side cover re-torque after cooler line removal and the TEHCM heat sink bracket. atracom.blob.core.windows.net (PDF)
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