The 6T75 transmission is a 6 speed automatic gearbox that was co-developed by General Motors and Ford for use of their mid-to-full-size FWD and AWD vehicles. Although the architecture is largely shared, the individual components and tuning are unique to each automaker. But regardless of the application, both the Ford 6F and GM 6T transmissions benefit from a space-saving design and advanced clutch-to-clutch shifting functionality.
What Transmission Do I Have?
If you’re wondering is the 6T75 transmission any good, the answer depends on several factors. First of which are the design flaws. The GM 6T75 transmission had a number of problems ranging from the infamous 3-5-R wavefront plate failures, to 6T75 TEHCM and valve body problems. If those myriad of issues have been properly addressed, then then this gearbox may actually perform quite well for you.
Common 6T75 Problems
6T75 wave the plate failure
Problem – The most commonly known issue with the 6T75 transmission is the failure of the 3-5-R wave plates. These metal discs provide both a cushion and gripping surface for the clutch discs during engagement of 3rd, 5th and reverse. Failure of the 6T75 transmission wave plates can cause those gears to initially engage harshly, followed very shortly by the complete failure of those gears.
Solution – Unfortunately, this is a very serious issue, and often results in the replacement of not only the waveplates, but the clutch drum as well. But that’s the best case scenario, as the broken metal discs often cause catastrophic damage to other transmission components, requiring a complete rebuild or replacement of the 6T75 transmission.
Problem – If the torque converter clutch/TCC solenoid fails to release as the vehicle is coming to a stop, the engine speed will be reduced below idle speed, causing the engine to stall. This solenoid is often damaged due to debris inside the transmission.
Solution – The valve control solenoid should be replaced, and the transmission control module will have to be reprogrammed in order to correct the problem.
One of the most common 6T75E transmission problems is overheating. This happens when the moving parts inside the transmission are creating more friction heat than the ATF can remove. The most common cause of this condition is towing heavy loads, driving in stop/go traffic, or on mountain roads where the transmission has to shift a lot.
Overfilling the transmission with too much ATF can also cause 6T75E transmission overheating, which can lead to ruptured seals, and damaged torque converters, valve bodies, bands, and clutches. An auxiliary transmission cooler can do a lot to help keep the temperature down.
Another common issue with the GM 6T75E transmission is broken waveplates. These metal discs help to lock gears together during a shift. If they break, the metal fragments will get hurled through the gearbox, causing catastrophic damage to other internal components. There isn’t a lot that you can do to prevent this problem, but a remanufactured GMC Acadia transmission can ensure that it won’t happen again.
6T70 / 6T75 TEHCM Problems
- 6T70 / 6T75 pressure control switch failure
- 6T70 / 6T75 solenoid failure
- 6T70 / 6T75 torque converter engagement and disengagement problems
- Slipping
- Limp mode
- Unusually harsh shifts
- Failed shifts
- Loss of gears
Common Causes of 6T70 / 6T75 TEHCM Problems
- Debris contamination due to poor maintenance and dirty transmission fluid
- OE component design flaws
- High mileage
- Extended severe use (towing, driving in the mountains etc.)
Common 6T70 / 6T75 Transmission Problems
Pressure loss from worn hydraulic circuits
Problem – As the various valves, pistons and checkballs move around inside of the 6T70 valve body and 6T75 valve body, the metal casting can wear out and allow hydraulic pressure to be a lost. This can lead to a number of valve body problems including:
- Loss of line pressure
- Burnt clutches
- Erratic shifting behavior
- TCC clutch function issues
- Torque converter clutch related DTCs
Solution – Repair or replace the valve body and self and install new pressure switches, accumulators, valves, checkballs, springs and other internal components.
4-5-6 accumulator piston failure
Problem – Another one of the common 6T70/6T75 valve body problems is the failure of the 4-5-6 accumulator piston. This is extremely important transmission part is responsible for smoothing out the engagement of the 4-5-6 clutches. However, excess wear in the bore, and to the piston itself cause a number of transmission problems including:
- Harsh and/or delayed 3-4 shifts
- Slipping
- Burnt clutches
- Gear ratio DTCs
Solution – Repair bores or replace both the valve body casting itself and the accumulator pistons.
Excess bore wear
Problem – Yet another common issue with the GM 6T70 valve body and 6T75 valve body, has to do with excess bore wear inside of the casting causing pressure leaks, which then leads to a number of transmission problems including:
- Unusually harsh shifts
- Unusually soft shifts
- Premature clutch failure
- Solenoid DTCs
Solution – Repair the bores or replace the valve body itself, then install upgraded internal components to compensate for the wear characteristics of this transmission.
Click here for a more in-depth look at 6T75 TSBs/technical service bulletins, 6T75 DTCs/diagnostic trouble codes and more.
Options to Solve 6T75 Transmission Problems
Buy a Used 6T75 Transmission
If you wanted to save some money, you could go down to the local junkyard and buy a used 6T75 transmission. But keep in mind, it’s coming out of a wrecked otherwise totaled vehicle. This means you don’t know how it was maintained, if it was abused or what the condition of the internal components really are. So you have no way of knowing if you are going to get 30 miles or 30,000 miles out of it. And that replacement warranty you get from the junkyard isn’t going to cover the labor cost that you’ll have to pay a mechanic to install a replacement transmission if the first used 6T75 breaks.
Buy a Rebuilt 6T75 Transmission
If you don’t want to risk future problems from a used transmission, then you might consider buying a rebuilt 6T75 transmission from a mechanic or transmission shop. In this scenario, they basically take your existing transmission and replace all of the main seals clutches and other “wear parts”. A rebuilt 6T75 transmission is obviously better than a used one. However, most mechanics and repair shops don’t have the experience and equipment to inspect every single component for signs of damage, warping and any other condition that might cause the parts to fall below the original manufacturer’s specifications. Plus that rebuilt transmission warranty may only be honored by a few local transmission shops.
Buy a Remanufactured 6T75 Transmission
Unlike a rebuilt 6T75 transmission, a remanufactured 6T75 transmission has been completely disassembled and then re-engineered on an assembly line. Each component is inspected, cleaned, and reconditioned by a technician that specializes in that particular stage of the process. All of the critical elements including the case, gears, valve body, shafts, pumps, and the torque converter are tested to ensure that they meet original equipment (OE) tolerances and standards. And any part that doesn’t meet the original specifications is either machined until it does or replaced with a brand new part.
Once all of the components meet specification, they’re sent down an assembly line and the transmission is reassembled. The reman 6T75 transmission is then put on a dyno machine which simulates real-world driving through a software program called C.A.R.S. This allows any leaks and imperfections to be discovered and dealt with before the transmission leaves the factory.
Another benefit of a remanufactured transmission are the updates and upgrades it receives. Once a certain vehicle model has been in production for a few years, small issues with the design are discovered and solutions are implemented. It may be more robust friction materials, stronger seals, stiffer springs, or number of other things. These changes are immediately applied to the new models still in production, and Technical Service Bulletins (TSB’s) are sent to dealers so they know how to deal with problems that may arise. Transmission remanufacturing companies like Street Smart Transmission also get these TSB’s, and implement the changes on their assembly line as well.
Warranty
We’ve already touched on it above, but given the complexity of this gearbox, it is extremely important that you consider what kind of 6T75 transmission warranty you’re going to get. Fixing a transmission is an extremely expensive affair, and should be treated like an investment. So let’s recap the ways that your investment will be protected:
Buy a used 6T75 transmission: This option has the lowest upfront cost, but it typically only comes with a 30 day – 6 month replacement warranty, which may or may not cover the labor charges if a mechanic has to remove and replace the transmission.
Buy a rebuilt 6T75 transmission: Depending on the competency of the mechanic rebuilding the transmission, this may be a more sensible option. However, a rebuilt transmission warranty is usually honored by just the repair shop/franchise that rebuilt it. So if you’re traveling far from home and suddenly have transmission problems, you might have to pay to fix your transmission yet again.
Buy a remanufactured 6T75 transmission: If you’re serious about keeping your vehicle on the road, then investing in a remanufactured 6T75 transmission is the way to go. If you buy one from Street Smart Transmission, then your investment will be protected with a 3-year/unlimited mile warranty. It covers all parts and labor, and can be used at any licensed repair shop in the continental United States. It’s also transferable should you decide to sell the vehicle. So if you don’t want to worry about unexpected transmission repair bills sneaking up on you again, this is definitely the way to go.
What Transmission Do I Have?
