Understanding ’19-Later GM 10-Speed Clutch Regulating Changes

In the past, we have had lots of discussions about clutch regulating valves, their relationships with clutch latch valves on many 6-speed transmissions and how they spilled into the 8-speeds. Now those parts have spilled into the 10-speed applications that are now hitting the shops.

For context, the clutch regulating valves and latch valves in 6- and 8-speeds, specifically the Ford 6R80 and ZF8, are controlled by solenoid pressure. At the beginning of the process, the solenoid amperage begins to increase (Figure 1A). But at a low amperage, this allows the regulating valve to be connected to an input from line pressure, which is routed to the latch valve, making a connection to the spring side of the regulating valve to help control the initial apply. When solenoid amperage is at its peak (Figure 1B), we see that solenoid pressure is at its peak and moves the latch valve to the right, cutting off connection to the spring side of the regulating valve. When this happens, the clutch is fully applied and connected to line pressure.

Figure 1 – 6R80 Forward Clutch: Regulated Apply vs. On

The Ford and GM first generation of 10-speed transmissions stuck with the latch valve for clutch control. But as we know it, these solenoids do not have a solenoid feed circuit for the clutch regulating solenoids. The 10-speed family uses a linear-force-type solenoid with an individual pin that contacts the regulating valve to control valve position and clutch regulation. Clutch apply begins as the LFS solenoid moves the regulating valve behind it, and pressure from the regulating valve is fed to the latch valve in between spools B and C (Figure 2A). The spool diameter of C is larger than B, so it begins to stroke the valve to the left, which regulates the feed pressure to the clutch apply through a narrow passage to the left of spool B. Figure 2B shows inlet pressure high enough to fully stroke the latch valve to the left, allowing full line pressure to be connected to the clutch apply.

Figure 2 – 10R80 Clutch Control: Beginning of Apply vs. Full Apply
During the beginning of apply, inlet pressure is fed to the clutch between spools B and C. Once the clutch begins to apply, that same pressure backs up and acts on spool C, which is larger than B. This begins to force the valve to the left, regulating apply pressure through the narrow passage to the left of spool B.
Once pressure from the inlet has built enough force to overcome the spring, the valve is fully pinned to the left. This connects line pressure to the clutch apply between spools A and B.

The Ford 10-speed family of transmissions, including the 10R140, stuck with the latch valve for clutch apply and control. The GM 10-speeds stuck with the latch valve until late 2019. Sonnax refers to this change for GMs as the second generation. These Gen. 2 valve bodies do not have the latch valves, but incorporated two new valves: the feed limit low and the feed limit high. These new valves work in conjunction with a new hydraulic clutch control circuit incorporating checkballs, which are referred to as “boost balls.” These checkballs act as a bathtub-type checkball, but fit into a normal pocket (Figure 3).

Figure 3 – ’19-Later GM 10-Speed: Feed Limit Low/High Valves & Boost Balls

Observing the clutch “A” control in relationship with the #5 boost ball, notice the boost ball is connected to the regulating spool of the “A” regulator valve. The new feed limit low valve output is fed below the #5 boost ball, seating this checkball against the separator plate when line pressure is below 120 psi (Figure 4A). When line pressure is above the limit spec of 119 psi and the #5 boost ball is unseated (Figure 4B), the clutch control regulating valve position will move to the right quicker since clutch apply pressure connected to the regulating spool behind the triple orifice is connected to the feed limit low circuit, which is limited to 119 psi.

Figure 4 – Clutch “A” Control in Relationship to #5 Boost Ball

Hopefully, this information will help in future diagnoses of clutch regulation issues. Knowing the different types and controls can give you the tools for a quick diagnosis.

Jim Dial is a Sonnax product line manager. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Transmission Company technicians.