Issue Summary:
- A ZF 5HP24 may exhibit a slipping or delayed engagement into reverse and/or drive before and after overhaul and also may have a flared kickdown shift to 4th.
- A V-8 BMW model with a 5HP24 may have a buzzing or droning noise coming from the area of the bellhousing.
- A Subaru vehicle equipped with the 4EAT Phase II has multiple solenoid codes with erratic transmission operation, which is commanded by the TCM.
ZF 5HP24 transmissions may exhibit a slipping or delayed engagement into reverse and/or drive before and after overhaul. A flare on a kickdown shift to 4th also may occur.
Inside the lower rear valve body there are two hard-plastic damper pistons (see Figure 1), one for the A clutch and the other for the C clutch.
The A clutch is used for forward and the C clutch is used for reverse (see Figure 2).
The original-design pistons have a center pedestal at the bottom that punches out over time, causing a leak in their respective circuits. Damage to the A or C clutch may occur, and if the valve body is not disassembled during the rebuild the original complaint will remain.
In a past ATSG seminar (2003), we noted that the pressure circuit for the EDS-5 solenoid has a rubber damper (bladder) in the channel plate that ruptures, causing a dumping to neutral on medium-to heavy-throttle takeoff and/or neutralizing during a 5-4 kickdown shift (see Figure 3). Many kits come with a new bladder to be installed during rebuilding of the unit.
The punched-out piston will need to be replaced. There is now an updated piston that eliminates the original bottom-center pedestal stop (see Figure 4).
The new-design piston has a split pedestal with a slightly increased thickness and diameter. The original ZF part number remains the same for ordering from an authorized ZF distributor for all models except Audi, for which there is an aluminum version that resembles the first design. Both the updated hard-plastic design with a split-pedestal stop and the aluminum damper piston with a single center-pedestal stop have the same dimensions and will interchange. The major difference is price. The aluminum version wholesales for about $27; the hard-plastic piston is about $4.
- Updated damper piston . .ZF Part # 1058-327-017
- Audi aluminum piston . . . .ZF Part # 1058-327-087
Some V-8 BMW models equipped with the ZF 5HP24 transmission may exhibit a buzzing or droning noise coming from the bellhousing area of the transmission. This noise may sound like a pressure imbalance from the volume-control valve in the pump or may even sound like a torque converter that is about to fail.
The cause of this problem is typically a valve resonance coming from the oil separator, which is situated at the back of the intake plenum, right above the bell-housing. It can be compared with the noise we have had on the 4EAT in the Ford Escort with a dirty PCV valve.
Testing: To verify whether this is the problem with this vehicle, start the engine and wait for the noise to start, remove the oil filler cap and see whether the resonance goes away. If it does, you will need to replace the oil separator.
To correct this condition refer to Figure 5 to locate the oil separator and replace it. Because of the part-number differences for the different models, you will need to contact your local dealer for the replacement-part number.
Multiple solenoid codes with erratic transmission operation, which will be commanded by the TCM.
Refer to the wire diagram in Figure 6 to see the TCM ground circuit, which is inside the transmission and is also the ground for the internal solenoids.
The physical ground point is shown in Figure 7.
It is a typical wire/eyelet through which a valve-body bolt goes. The ground wire then travels through the case connector at terminal 16 (see Figure 8) and continues to terminals 9 and 19 at the TCM, where it serves as ground for the TCM as well.
Make certain this ground is in good condition as well as tight to ensure a good ground. Since it serves as ground for both the transmission solenoids and the TCM, a variety of complaints could arise as a result of this ground being faulty.
May 2008 Issue
Volume 25, No. 5
- ZF 5HP24: Delayed or Slipping Forward and/or Reverse; 5-4 Kickdown Flare
- BMW 5HP24: Buzzing or Droning Noise from Bellhousing Area
- Subaru 4EAT Phase II: Erratic Transmission Operation