Shift Pointers
- Author: David Chalker, ATSG Technical Consultant
Ruptured damper plug in ZF 5HP19 FL/FLA can cause neutralizing in 1st or 2nd
The ZF 5HP19 FL/FLA automatic transaxle has had its share of problems during its tenure, fitted in the Audi A4, A6 and A8 and the Volkswagen Passat. One concern we have been dealing with recently on the tech line at ATSG is the complaint of neutralizing under a heavy throttle in first or second gear.
Under light or moderate throttle positions, the vehicle appears to function correctly and upshift OK; however, under heavy acceleration either from a standstill or being driven in first gear, when the transmission shifts into second gear or is being operated in second gear, it feels as if it goes into neutral. When the transmission is removed and disassembled, it is apparent that the G clutch has been slipping, because the frictions normally are quite burned.
The root cause of the burned clutch may not be apparent during initial inspection, especially if the technician does not take the time to disassemble the valve body. In the channel-plate section of the valve body are three rubber damper plugs. These damper plugs act as accumulators for the pulse-width-modulated solenoids EDS 2, EDS 3 and EDS 4. The damper plugs must be removed from the valve body and inspected carefully. The reason they must be looked at carefully is because of their tendency to “rupture” or “burst.”
If you experience a similar neutralizing effect during heavy acceleration, the EDS 3 damper assembly will be the suspect you want to investigate. The EDS 3 solenoid is pulsed on in reverse, neutral, and 1st and 2nd gears. The partial hydraulic drawing in Figure 1 shows that modulator pressure is fed to solenoid EDS 3. With the solenoid on, modulator pressure flows to the EDS 3 damper-piston assembly and then strokes the G-clutch shift valve and G-clutch accumulator control valve, allowing line pressure to apply the G clutch.
During heavy-acceleration conditions, increased modulator pressure can cause a “rupture” or “burst” hole to occur in the plug, allowing oil to exhaust through the channel plate. When this occurs there will not be sufficient pressure to stroke the G-clutch shift valve or accumulator control valve, which will lead to a partial apply of the G clutch and a neutralizing condition.
The photo in Figure 2 shows the channel plate with the EDS damper-plug locations and the exhaust holes in the channel plate. These rubber damper plugs were used in ZF5HP19 models through 1999. During model year 2000, ZF introduced an updated damper assembly. The photo in Figure 4 shows the early-style damper plug and the later damper piston.
Now take a look at the partial hydraulic diagram in Figure 3, which illustrates the same partial hydraulic circuit except that it shows the new-design EDS 3 accumulator piston. Notice the top of the accumulator piston. There is no orifice as in the previous plug; instead, the surface is solid and in the bottom of the plug is a rubber insert that provides the cushion, or accumulation. The solid top obviously prevents rupturing, and these new pistons eliminate the problem.
Take a look again at Figure 4. In the photo you will notice the updated piston shown on the right with no top orifice and the rubber damper insert at the back. You will also notice the piston is aluminum in contrast to the earlier rubber plug. A difference not as obvious is the outside diameters of the old rubber plug and the new aluminum piston. The outside diameter of the rubber plug is about 0.458 inch, whereas the outside diameter of the aluminum piston is 0.471 inch. Since the accumulators differ in diameter, the bores in the two channel plates must have different diameters. The bore in the channel plate to accommodate the early rubber damper is 0.315 inch, whereas the bore in the later channel plate for the aluminum piston is 0.471 inch.
Figure 5 shows the new-style channel plate. Since the accumulator-piston bore’s diameter is larger, the aluminum pistons cannot be used in the early channel plate; therefore, if you have a rubber damper that is ruptured, you will have to use a new rubber damper.
If you want to use the later-style piston to prevent a future incident, you will need to buy a new channel plate, separator plate and pistons from a ZF-authorized distributor. Most overhaul kits will come with both the rubber plugs and the newer pistons, so if you have a kit you will need to buy only the new-style separator and channel plates. The ZF part numbers for these items are:
These updated parts cost about $100 or so, which, in my opinion, isn’t a lot to spend to prevent a costly comeback, and after you’ve updated to the later parts, we hope this unit won’t “burst your bubble.”