In 2019, some Chrysler/Ram/Jeep applications that utilize the ZF8HP transmission moved to a second-generation unit with a new designation and numerous changes for better performance and durability. Gen. 1 units are classified as 8HP45, 8HP70 and 8HP90 and Gen. 2 as 8HP50, 8HP75 and 8HP95. Internally, the Gen. 2 transmission had numerous hard part changes due to a change in gear ratios. Controls also went through numerous changes, as one of the clutch/brake-related circuits was eliminated.
Figure 1 shows a cutaway view of the Gen. 1 “A” and “B” brake assemblies which are located in the back of the pump housing. Note that the Gen. 1 “B” brake piston has an apply circuit “B1” and release circuit “B2” (Figures 2 & 3).
|Figure 1 – Gen. 1 “B” Brake Components|
|Figure 2 – Gen. 1 Pump Housing||Figure 3 – Gen. 1 “B1” & “B2” Piston Identification|
Figure 4 shows a cutaway view of the Gen. 2 assemblies where you can see the Gen. 2 “B” brake piston only has an apply circuit, as the “B2” circuit was eliminated and was replaced with a return spring assembly (Figure 5). The Gen. 2 clutch plate assemblies also had wave springs added between each of the steel plates for both the “A” and “B” brake assemblies to provide quicker clutch/brake release (Figure 4).
|Figure 4 – Gen. 2 “B” Brake Components|
|Figure 5 – Gen. 2 “B” Brake Piston Return Spring|
With the change to Gen. 2, the valve body also went through some major changes with the elimination of the “B2” hydraulic circuit. Refer to Figure 6 for a view of the Gen. 1 valve body. Note the locations of the normally high and normally low solenoids, and also note that there are five valves in the upper valve body casting.
|Figure 6 – Gen. 1 Valve Body|
Refer to Figure 7 for a view of the Gen. 2 valve body. Note the locations of the normally high and normally low solenoids. Notice that the “B” and “D” solenoids have swapped positions with the Gen. 1 locations. These Gen. 2 solenoids have the new-style cream and blue caps on them, but they are not interchangeable with the 845RE solenoids that came out in late 2014 as the snout diameters are different. Also notice that there are no control valves in the upper valve body casting.
|Figure 7 – Gen. 2 Valve Body|
Jim Dial is a Sonnax technical specialist. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of industry technical specialists, transmission rebuilders and Sonnax technicians.
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