Don’t Let This Burst
Your Bubble
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 on page 16 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 on page 32 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 ZF 5HP19 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 on page 32, 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.” 
©2005 Transmission Digest
