ZF9HP48 FWD Nine Speed, Part 2

Technically Speaking

Author: Mike Riley, Technical Editor
Subject Matter: 9-speed transmission
Unit: ZF9HP48
Issues: Noteworthy features

(Is This Fuel Economy or Marketing Driven?)

ZFhas outpaced other transmission manufacturers with the nine-speed ZF9HP48 (Chrysler 948TE) FWD. The unit is extremely compact, considering what it does. Unlike the 8HP family, the 9HP is not a mechatronic design. The 9HP uses a torque converter; however, a hybrid version, the 9P48H, will utilize an electric motor instead. The unit, which weighs in at nearly 200 lbs., can be equipped with a mechanical or electronic pack arrangement.

What makes the 9HP so compact is the nested planetary design. There are actually four planet sets and the layout is uncommon. At each end of the assembly are two rotating clutch drums and in the center is the out-put gear and support (Figure 1). The input shaft runs the length of the assembly. The “C” and “D” brake hubs are also part of the planet section. The end hub is for the “C” brake and the front hub is for the “D” brake.

The first rotating clutch assembly seen with the bell housing removed is the “E” clutch. The drum is steel and has sensor knockouts for the input-speed sensor (Figure 2). The “E” clutch piston is bonded and there is a bonded sleeve pressed onto the drum similar to the 4T40E. The steel retainer compresses a Belleville return spring. The frictions are segmented and the clutch pack uses a cushion spring. The drum is splined to the input shaft and the clutch is applied in 4th through 9th gears.

The “E” clutch hub is steel and the shaft extends through the assembly and splines to the number two planetary (Figure 3).

The output gear support serves two purposes. First, it provides the surface for the output gear bearing and nut for gear rotation as well as the component center line. Secondly, it is part of the apply mechanism that makes the 9HP different from other automatics: the dog clutch. A dog clutch is a form of synchro assembly that provides a mechanical connection (Figure 4). The dog clutch in this position is the “F” dog clutch and its purpose is to anchor the common #1/#2 sun gear to the output gear support. The dog clutch sleeve is splined to the support and when applied meshes with the sun gear. The sleeve has two sealing rings for apply and release and will move quickly. The “F” dog clutch is engaged in park/neutral and reverse as well as 1st through 4th gears.

The first planetary in the set is merely referred to as planet #1, which is a four-gear planet carrier. The #1 planet carrier splines to the output gear and also has an oil dam. The #2 planet carrier contains the ring gear for the #1 planet (Figure 5). The #2 planet is also a four-gear design. Both planetaries share a common sun gear, which can be held stationary by the “F” dog clutch. Note the synchro splines at the end of the sun gear.

The two remaining planetaries are a bit more involved and contain another unique feature that other automatic transmissions do not have. The #3 and #4 planet sets are contained in the same housing, which is aluminum and has splines for the #2 ring gear (Figure 6). The sun gear for the #3 planet and the ring gear for the #4 planet are actually the same part. Beyond that, the center of the sun gear/ring gear has a synchro spline for the “A” dog clutch. In effect, when the “A” dog clutch applies the sun gear/ring gear is locked to the input shaft. The #4 sun gear is made to the aluminum “C” brake hub which is snap-ringed to the “D” brake hub. The “C” brake hub also has splines for the “B” clutch steels.

The remaining friction element is the “B” clutch assembly, which is splined to the input shaft. The clutch pack is inverted, in that the frictions have external teeth and the steels have internal teeth. The clutch drum is aluminum, as is the apply piston (Figure 7a). The clutch pack also uses a cushion plate and the frictions are segmented. The piston-return spring is the Belleville design. The “B” clutch is applied in reverse, 3rd, 5th and 9th gears. The second dog clutch (“A” dog clutch) that the 9HP uses is also positioned onto the input shaft directly in front of the “B” clutch drum. Oil pressure in the center of the input shaft will move a valve that is connected to the dog clutch for apply and release (Figure 7b). The “A” dog clutch is applied in 1st through 7th gears.

Closely inspect both dog clutches for spline wear. The transfer gear and differential assembly are fairly straightforward and resemble many other front wheel-drive applications. Both the transfer gear and differential are supported by tapered roller bearings and the transfer gear/pinion gear has the park gear made to it (Figure 8). The differential carrier can accommodate 2WD or 4WD applications.

The valve body for the 9HP48 can accommodate a couple of basic modes of operation. The transmission can be equipped with either a mechanical or electronic park system. If the transmission merely has a mechanical park, then the valve body contains a total of nine solenoids, (Figure 9). If the transmission is equipped with an electronic park, then the valve body will have 10 solenoids, one extra for the park system. Beyond the multiple solenoids, the remaining aspects of the valve body are pretty basic. When reassembling the valve body halves, ensure that the manual valve is rotated correctly to engage the lineup notches. Mark all solenoids before removing.

Unlike many other transmissions, the 9HP uses a slew of connecting tubes, all of which contain O-rings. The connecting tubes connect the valve body directly to the pump housing as well as the filter assembly. In addition, there are two tubes that connect the valve body to the output gear support and have a unique design (Figure 10). Due to the narrow support design, one end of both tubes had to be elongated to provide proper oil volume. The valve-body end of the tubes is round.

The solenoid connector plate for the valve body is comprised of several components that must be handled carefully. Beyond connecting to the solenoid terminals, the connector plate contains the wiring for the input/output speed sensors as well as the internal mode switch (IMS) and TFT. The main electrical case connector, which extends through the valve body cover, is also wired to the connector plate (Figure 11). The valve body must be removed to gain access to the input/output speed sensors and internal mode switch, therefore use caution to avoid damaging the wires. TD