Audi A8 Quattro - Transmission Digest

Audi A8 Quattro

If you have ever driven an Audi A8 or any other high-end car using a ZF 5HP19 or 5HP24 transmission, you know these units are pretty smooth shifting and lockup is almost undetectable. This particular Audi came in with a customer complaint of a clunk or bump when the vehicle slowed. Initially, the car was diagnosed, and the unit was removed and rebuilt.
Audi A8 Quattro

TASC Force Tips

Authors: Bob Warnke & Brian Workman

ZF 5HP24 TCC Cycling Bang

TASC Force Tips

  • Authors: Bob Warnke & Brian Workman

ZF 5HP24 TCC Cycling Bang

One of the benefits of being a part of the Sonnax TASC force is the sharing of information and ideas that goes on between members. Knowing that someone else has been down the road you are on and may have learned about or at least worked on the same problem you are facing is always reassuring. It is not uncommon for members to share their hard-earned knowledge with each other and with other industry contacts as well.

In this case, knowledge shared between European and U.S. TASC members reached outside the group to help a non-TASC member. Brian Workman does hotline duty and other technical chores for Cottman Transmissions. Not one to forget a favor, Brian shares with you what he learned.

If you have ever driven an Audi A8 or any other high-end car using a ZF 5HP19 or 5HP24 transmission, you know these units are pretty smooth shifting and lockup is almost undetectable. This particular Audi came in with a customer complaint of a clunk or bump when the vehicle slowed. Initially, the car was diagnosed, and the unit was removed and rebuilt. The converter was cut open, inspected and welded back together. The unit was reinstalled, bulk fluid was used to refill it and then it was road-tested. Unfortunately, the problem was still there. When I received the call, it was described to me as going in and out of lockup while slowing from 80 to 60 miles an hour and then, magically, it stopped.

The easiest thing to check first is the nose switch on the throttle-position sensor; it tells the computer when you are at closed throttle. If it were malfunctioning, the computer might see the switch opening and closing, causing the problem. The technician tested the nose switch and said the contacts opened and closed perfectly.

At this point, we had to answer the following question: Is the transmission shifting the way the computer is commanding it to or is there still a problem in the unit or the converter? Hooking up a DVOM to the ground lead of the TCC solenoid will let you watch the TCC command from the computer. If the computer is commanding the TCC on and off, you should see voltage go up and down. That is exactly what was happening. Why would the computer command the lockup on and off while the vehicle was slowing? Many imports pulse their lockup on and off when slowing, but this one you could actually feel. You could compare the feeling with stepping on and off the brakes fairly hard. In addition, there was another problem present. The unit had a clunk when coming out of third gear. It was staying in lockup until it downshifted into second.

In this situation, the shop had a SOLUS Pro with the VAG Com software. This made it possible to do some thorough diagnostics before attempting any further repair. Watching the data on the scan tool, nothing jumped out at as being wrong. Throttle position, mass air flow, the nose switch all appeared good. With this particular problem, what you need to watch is trans temp, TCC slip and TCC-solenoid amperage. The scan tool will have the TCC solenoid labeled as DCSV 4. That stands for damper-clutch solenoid valve. These particular parameters are found under Trans Data Logs. There are many log files, so you will have to do some searching to find the right ones. Remember to set your scan-tool view to 4 graph mode.

Watching those three parameters during the road test, you will see that TCC-slip rpm and solenoid amperage are inversely proportional. As TCC amperage goes up, the lockup piston is applied more and TCC slip will go down. Figure 1 is a snapshot of the recorded data. Where TCC slip is high, the amperage is low, 0.144 amps. At 0.744 amps, maximum TCC apply is being commanded. Watch the amperage as the vehicle was slowing. It was being toggled down 0.736 amps, then right back up to 0.744 amps. That is a clear indication that the computer is commanding lockup cycling. Where you see the sharp spike is where you would feel the bump.

Amperage should not change unless the computer picks up a slip. Just as with a GM or Ford, when you see TCC duty cycle go to 100%, you know the unit is commanding full lockup. Could the clutch be slipping? Could the valve body be worn like those on a GM or Ford? The graph in Figure 1 shows that there is TCC slip. You replace the valve body first and see whether that makes a change. With the replacement valve body installed, the second road test proved there was a problem with the original valve body. The unit now shifted more smoothly and lockup was better (not as hard), but still not right.

Figure 2 shows the same parameters that were graphed in Figure 1. The difference is that the amperage spikes are not as sharp. You can see the small ramps as TCC amperage is increased and then drops off. What was seen on the scan tool matched what could be felt on the road test.

After making a few phone calls to get some feedback on these units, I learned from contacts at Sonnax that these ZF units are known to have converter problems, and this complaint is very common, according to the builders in Europe. In fact, these converters are so problematic, the builders recommend using a tested ZF or a ZF rebuilt converter with synthetic fluid. The shop I was helping ordered a high-end remanufactured converter. The unit was expensive, but the results were worth it! Installing the converter and using synthetic transmission fluid gave us phenomenal results. Not only did the transmission shift more smoothly than before, but also lockup engagement was undetectable. The only way you knew it was in lockup was to look at the scan tool.

Figure 3 shows the data from the final road test. On TCC command you see amperage go to 0.744 and you are in full lockup. TCC slip is 0 rpm. On closed throttle you can see TCC desired amps drop to 0.416 and remain steady. TCC slip is minimal. No more spikes, no more ramping of the TCC solenoid and, most important, no more TCC thump or bump. When the vehicle is slowing to a stop, desired amperage will remain at 0.416 until the transmission is commanded into second gear. At that point lockup is turned off and desired amperage drops to 0.144. Again, you won’t feel any thump or bump.

With this type of torque converter and programming, the computer tries to control TCC slip on deceleration. If it can’t get the transmission input speed in line with the engine speed, the computer will keep increasing the amperage until it reaches full lockup. There is the bump. At that point, it saw that the ratio between the two speed sensors was not what the program intended, and it immediately reduced the TCC-amperage command. In this case the computer’s inability to control the slip was caused by a worn-out lockup-clutch lining. In the transmission, when frictions wear, clutch-pack clearances and piston travel increase. The same thing happens with torque-converter lockup clutches and linings. This added piston travel resulted in the thump or bump you felt going in and out of lockup. These ZF units use a captive-clutch design. Two characteristics of this design are the critical importance of piston travel on lockup function and the difficult disassembly, inspection and rebuild process. This could be why the converter was not repaired or replaced when it was initially cut open.

Another factor that contributed to the problem we experienced was a worn pressure-regulator-valve bore, which resulted in higher line pressures. Since main line has an effect on all pressures in the unit, high line causes high converter-charge pressure.

Remember that all ZF 5HP19s and 5HP24s have this captive lockup clutch. If you happen to get a car in with this transmission and complaint, use a good converter, check the pressure-regulator-valve bore for wear, and always use a good full-synthetic transmission fluid.

For more information on captive clutches, see technical articles by Joe Rivera in December 2005 and Ed Lee in March 2007 Transmission Digest.

Bob Warnke is Sonnax vice president of technical development and a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.

Brian Workman is technical trainer and consultant for Cottman Transmissions LLC. In addition to his technical-hotline duties, Brian is a technical instructor, speaker and author of newsletter and magazine articles.

You May Also Like

Trying to Stop the Wheel Hop on Ford Edge with 6F50 Transmission

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a viscous coupling assembly controlled by an Active Torque Control (ATC) coupling solenoid. The system is designed to monitor vehicle conditions continuously and seamlessly adjust torque distribution between the front and rear wheels. When it is functioning correctly, there should be no perception of this taking place when launching or driving the vehicle. 

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Related Articles –

ab60
GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – TASC Force Tips: Hydraulics Fundamentals: Check Valves – Shift Pointers: Mazda Sensitive to Pressure – Transmission Testing & Repairs:

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

Other Posts
GM 9T series: Critical wear areas, vacuum test locations

Sonnax has provided the following guide on critical wear areas and vacuum test locations for the GM 9T series of transmissions. Technicians working on these models should find this guide helpful. Related Articles – Solving a 4L60E acceleration shudder puzzle – The transmission repair industry: Globally integrated – Shift Pointers: A 10R140 with a classic

TASC-Tip-1400
The torque converter can of worms: Lockup and aftermarket programming

Lockup torque converters have been around now for some time. They came into production around the time when fuel mileage demands were put into effect by the government, and the auto manufacturers needed to do something to better connect the fluid coupling (torque converter) of the automatic transmission to the motor. By doing this, OEMs

tascfeature-1400
Watch out for high pressure in GM 8L45, 8L90 valve bodies

Hey now! Oh boy, do I have a fun failure to share with you and warn you about today! Related Articles – Shift Pointers: Where’s that fluid leak coming from? – Multitasking: Sorting out multiple issues with the same vehicle – Chrysler RH/RE late shifts and high pressure Have you encountered a crack in the

Shift of the shaft: Diagnosing Chrysler 48RE manual shaft issues

The TorqueFlite transmission has been around since mid-to-late 1950s. There have been many changes surrounding the manual shaft and rooster comb through the years. This transmission shaft controls the position of the manual valve that directs oil for the gear ranges, but it also is used for a Reverse light control as well as Park/Neutral