The 10L1000 was introduced in 2020. It replaced the Allison LCT 1000, which has been around for more than 20 years. The LCT 1000 is an excellent transmission with an excellent reputation, rooted in the customer’s belief that they own the best transmission on the market. Unfortunately, very few customers know which transmission is in their vehicle. However, customers that drive a 3/4 or 1-ton Chevrolet/GMC happily identify their vehicle not as a Silverado or Sierra but as a Duramax-Allison application.
The 10L1000 is a 10-speed heavy-duty transmission that shares some design features with its smaller light-duty 10-speed cousins. However, although the 10L1000 looks much like a 10L80, it is much larger with a higher torque capacity. In addition to being a more robust unit than the 10L80, it is much heavier, weighing in at over 360 pounds. The transmission has 6 or 7 multiple disc clutches, four planetary gearsets, an off-axis gear-driven vane style oil pump, and a remote-mounted TCM.
Shops are starting to see the units coming in for repair. If it is a 4wd application, my words of wisdom are to get someone to help you to remove and install the transfer case on this application. The transfer case is heavy and quite large, so it is cumbersome to manage. In addition, the cross member cannot be removed, so you will need to maneuver the transfer case around the cross member.
The transfer case has a cutout on the top of the case and a rubber plug that will need to be removed when removing or installing the unit (figure 1). The transfer case requires that you tip the unit at about a 60-70 degree angle to allow the transfer case to clear the transmission output shaft. There will be very little clearance between the output shaft and the top of the transfer case. Since the transfer case is so large and heavy, this is not a “one-man show.”
You may be wondering why one would need to remove the transfer case. The simple answer is we are starting to see some issues with one of the clutches in the 10L1000 transmission. As I explained in an earlier gears article, the 10L1000 utilizes 6 or 7 multiple disc clutches, depending on if the unit is equipped with a PTO. If the unit does not have a PTO, the transmission will be fitted with six clutches. In PTO applications, the case is a different design, and the PTO and its clutch are housed in the offset portion of the PTO design case.
Since so many gears are available, four clutches are used to change the ratio from gear to gear. Which four clutches are in operation will determine which gear ratio the transmission produces. The 10L1000 clutches include:
- 1-2-8-9-10-R (C1)
- 1-2-3-4-5-6-R (C2)
- 2-3-4-5-7-9-10 (C3)
- 1-2-3-4-6-7-8-10-R (C4)
- 4-5-6-7-8-9-10-R (C5)
- 1-3-5-6-7-8-9 (C6)
- PTO
The 1-3-5-6-7-8-9 clutch is connected to the input shaft and housed in a drum as a rotating clutch (figure 2). The backing plate for the clutch is built into a support. A snap ring holds the drum and clutch together. If you see a clutch issue with this unit, it will typically be the 1-3-5-6-7-8-9 clutch.
The support design lends itself to the clutch failure issue you may be experiencing, as the integral backing plate does not fully support the clutch components (figure 3). The minimal support leads to clutch “flex” issues which leads to a burnt clutch (figure 4).
I am sure it will not be long before GM redesigns the support, as this is a common issue. However, the aftermarket recognized the problem early on, so ask your parts distributor about available components.
When working on the 10L1000, remember that the components are heavy, so take care so that you do not injure yourself. Until next time, remember, “Good cars get you from point A to B, while great cars just get you in trouble.”
