GM 6L80 Transmission Early Failure Issues & Fixes - Transmission Digest

GM 6L80 Transmission Early Failure Issues & Fixes

Sponsored by Reman Transmission

The application use of the 6L80 transmission has been extensive over the years. General Motors originally manufactured this transmission. It was designed for both AWD/4WD and RWD General Motors applications. The 6L80 has unique operations, such as an advanced computer controller constructed into the valve body and a direct clutch to clutch shifting.

The gearbox was created to manage a maximum torque rating of up to 650 lb-ft from some of the most significant engines GM had to offer. However, some design flaws of the GM 6L80 led to various transmission issues which have been presenting themselves over the last 5 years or so. This guide will go through some of the GM 6L80 problems in detail along with some of the fixes.

What Are Some of the Common Issues with 6L80 Transmission?

The 6L80 has had a load of transmission problems, some of which directly inhibit drivability. Some of the most common issues include:

  • Cracks in the 1-2-3-4 pistons
  • Slipping 2nd and 3rd gears
  • Cracked drum
  • Skipping 2-3 gears
  • Clutch Failure
  • First Gear Slipping
  • Reverse gear engagement failure
  • Cracked clutch drum
  • Stator support issues

Cracks in the 1-2-3-4 Pistons

Issues with the 1-2-3-4 pistons are common in 6L80 transmissions. The piston typically gets cracks that result in clutch failure. However, GM updated the piston. Therefore, it will be wise to update the piston to the latest designs. 

Also, the piston housing may crack. This is, however, not as common as the cracking of the piston itself. The housing’s inner diameter develops a crack and may break away from the accommodation. This will result in 1-2-3-4 application problems. Transmission remanufacturers like Reman Transmission will correct the problem by installing updated versions of the 6L80 1-2-3-4 pistons and the housings with them. General Motors also updated the housing to resolve the issue but this is only on the most recent version of the gearbox.

Cracked Drum

Another significant problem is a crack that affects the drum weld. The result of the crack is usually a 3-5-R clutch issue and failure. Typically, rebuilders weld these cracks. This becomes a short-term solution for a long-term problem as more problems will arise later on when the welds slowly weaken and fail. If that doesn’t happen first, another crack somewhere else on the clutch typically does. 6L80 transmission rebuilders will now install an updated version of the 6L80 clutch drum to resolve the problem accordingly.

Stator Support Issues (Failed Seals and Cracking)

You should pay close attention to your stator tube cracks and sealing rings, but that’s pretty hard to do considering they’re on the inside of your transmission. On the back of the stator support, there are seal rings. These cover the feed oil circuits for the 3-5-R and 1-2-3-4 clutches. The units that came out earlier had issues with the ring’s design, resulting in leaks mostly during cold operation. The result was mostly a slipping or delayed engagement that went into reverse.

General Motors came up with an update for the seal rings on the support to curb the problem. However, the updated design does not fit the earlier design pumps. Therefore, you may be required to replace the pump entirely. Alternatively, you could have the pump machined, which would allow you to fix the updated rings.

Depending on where the crack develops, the crack may lead to clutch failure, mainly to the 4-6-5 clutches. Also, there are problems with the stator support tube or the liner developing cracks. These issues are not common, but they may occur. Therefore, it will be good to take a minute to examine your stator support ID if you’re having trouble with your transmission and are mechanically savvy.

Reverse Gear Engagement Failure

The reverse gear is critical for the drivability of any vehicle. It is not uncommon to find the reverse gear of a 6L80 failing to engage, which points to a possible problem with the transmission.

The signs of a reverse gear engagement failure can be; difficulty in engaging the gear or no gear is not engagement. This issue is best solved by heading to a trained mechanic because there are a few mechanical issues that could cause this problem.

Slipping 2nd-3rd Gears

Slipping from 2nd to 3rd with a 6L80 transmission is unfortunately a common experience among Chevrolet and GMC pickup truck owners. This slipping problem results in a difficult time utilizing any of the gears. As a result, the vehicle will consume a lot of fuel.

In some instances of slipping, you will hear a sound indicating there is a slip. This will be a good indication of a slip. If you use a diagnostic tool, an error code will be displayed. The most common error code for this problem is P1870 which indicates a slipping transmission component.

To curb this problem, the solenoids of the two gears will have to be repaired or replaced. This is because the problem primarily stems from worn-out solenoids. Though fairly rare, there are instances of total mechanical failure with this problem.

Inadequate Torque and Acceleration from the First Gear

Slipping in the first gear can result in poor acceleration and torque. Typically, you will feel a sense of loss of acceleration on pressing the throttle pedal in first gear. Also, the diagnostic tool will indicate the P1870 code when you connect it with the transmission control unit.

To diagnose and possibly fix this issue, you will need to check the condition of the transmission fluid in the system as well as the solenoids. As non-synthetic fluid and worn-out solenoids are often the reason for the problem.

Clutch Failure

Clutch failure is relatively easy to diagnose. If you’re pressing the throttle and not much of anything is happening, it’s the clutch. When there is a complete failure, the car will not move entirely.

The 6L80 has a friction type of clutch. Therefore, you must examine the friction plate in the clutch assembly of the 6L80 transmission. Necessary repairs should be conducted if there are any problems detected. Most of the time an updated clutch assembly installation will clear this problem but not always so it is imperative to always let a professional take a look.

Low Sprag Problems

6L80s with high mileage will have problems akin to the 1-2-3-4 clutch operation. However, these problems will have no relation to the operation of the clutch.

A sprag with issues will have the L/R clutch holding the output carrier at first when driving. After the vehicle gets to 2 MPH, the L/R clutch releases. When the spag doesn’t hold, the car drops to neutral. This creates the impression that the 1-2-3-4 clutch has failed.

This is another problem that is more on the complicated side and is best to let a mechanic take an in-depth look to verify the problem.

How Transmission Remanufacturers Address GM 6L80 Issues During The Rebuild Process

Some of the problematic parts of the 6L80 are replaced or upgraded by transmission manufacturers. For example, some of the upgrades Reman-Transmission performs include:

  1. Boost planetary covers and sleeves are replaced.
  2. Prevention of cracking at the welds by updated drums.
  3. They have detailed the fluid pump with machined pump body mating surfaces and resurfaced pump rotor mating surfaces to keep fluid pressures at the right point.
  4. Installation of a low sprag 38-element in the units to boost the holding capacity.
  5. Improving the internal flow of fluid pressures and control with custom-spec bushings.
  6. Elimination of seal leakage by late style stator support shaft with modified seal rings.
  7. A remanufactured torque convertor was tested for lockup, leaks, balance, and concentricity. The upgrades remove the possibility of early bushing wear and eliminate the risk of front seal leaks.
  8. Prevention of weld cracking by updated drums.
  9. Proper transmission testing includes a filtration system and fully synthetic automatic transmission fluid.
  10. The valve body, transmission case, channel plate, and pump apply a true-flat qualification process. They prevent pressure losses and cross leaks.

Apart from significantly modifying your 6L80 to curb all common issues, Reman-Transmission also has lower 6L80 transmission prices than all the big box stores. Buying a 6L80 for sale from Reman-Transmission, will save you money on the transmission and down the road since all the common issues have already been fixed. 

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