Valve body in automatic transmissions. Principles of operation. Problems and repair procedures. Valve body Testing Equipment

All automatic transmissions are equipped with a valve body, which plays the role of the main control unit. Basically, the valve body is a hydraulic “controller” (also called as a “transmission brain”) consisting of valves, solenoids, sensors batteries and attached to them are passages and channels, which guide the flow of automatic transmission fluid (ATF) to various valves with the purpose to activate required clutch and shift the gear properly according to the driving situation.

The modern valve body is controlled by means of electrical signals from TCM (transmission control module) and distributes/directs the oil pressure from the oil pump to an appropriate clutch drum to shift gears and lock the torque converter. Valves that operate in the valve body serve different purposes and their names reflect what they do. For example, the valve body has a 2-3 shift valve which is responsible for up shifting from 2-nd gear to 3-rd gear. And if there’s going to be a downshift from the 3-rd to the 2-nd gear, then the 3-2 shift valve would perform this operation.

Following videos will give you more insight into automatic transmission valve bodies

Valve Body Positioning

Generally, the valve body is located inside the gearbox and is protected with the cover. But when repair specialists have to check the valve body, it may be a challenging task for them to reach the valve body. The fact is that in some gearboxes (such as 09G and 5hp19) the valve body is positioned at the bottom part of the gearbox and specialists have a direct access to the protection cover (when the car is lifted However, in gearboxes manufactured by Volvo, Peugeot, Opel and SAAB, the valve body (in most cases) is located on the side of the gearbox and a direct access is impossible, therefore specialists have to use special instruments to do that.

Learn how to remove transmission valve body

Classification of valves

The gearbox valve body includes a number of different valves, namely:

Pressure control valves

• These valves are responsible for the pressure control inside the gearbox and in their turn fall into several groups:
• The primary regulator valve, which specifies the volume of ATF transmitted from the gearbox pump.
• The secondary regulator valve, which adjusts the pressure of ATF transmitted to the torque converter.
• The oil cooler bypass valve, which regulates the pressure of ATF flowing to the ATF cooler; this valve locks the oil circuit via the oil cooler when the oil is still cold (it operates as the thermostat in the engine cooling system). This valve provides constant temperature of ATF.
• The pressure relief valve, which controls or limits surges of pressure within the oil pump and prevents any redundancy

Shift Control Valves (Solenoid Operated Valves)

These valves are considered to be a two-position control device which can be in On (Open) and Off (Closed) operational conditions. ATF flows via these valves to spool-type control valves, which open or close channels intended for transfer of ATF to actuators of gear shifting mechanisms. In modern electronic automobiles, they’re controlled by solenoids, while in older models, they’re driven by hydraulic pressure. Control valves open in accordance with the current passing through their windings and change the pressure of ATF in the mainline. These valves are divided into the following subtypes:

• The manual valve, which operates as the main control unit and distributes ATF to different areas of the gearbox
• The 1-2 shift valve, which is responsible for shifting from 1-st to 2-d gear
• The 2-3 shift valve, which is responsible for shifting from 2-nd to 3-rd gear
• The 3-4 shift valve, which is responsible for shifting from 3-rd to 4-th gear

Note: shift valves may perform upshifting and downshifting operations (for example, from 1-st to 2-nd gear and vice versa), but in some transmissions upshifting and downshifting functions are divided between separate valves.

Timing valves

These valves interact with the shift control valves. They are responsible for proper and well-timed gear shifting. In advanced gearboxes, these valves also help to enhance fuel efficiency. They include :

• The downshift timing valve, which hinders random downshifting from overdrive.
• The accumulators, which soften gear shifting operation with the help of spring stiffness to counter ATF pressure

Pressure Modulating Valves

These valves help to adjust the volume of ATF in the gearbox at any time. They include :

• The cut-back valve, which controls throttle pressure as the car changes speeds, ensuring that the pump always provides the right volume of ATF
• The governor modulator valve, which lowers the load applied from the engine to the gearbox at high speeds

Typical Valve Body Problems

Typical symptoms of the valve body failure in automatic transmissions occur in the form of increased vibration and scraping noise when shifting gears. In many cases issues with the valve body become evident because of jolts, kicks and slipping between gears. Frequently, the necessity for valve body repair is caused by ill-timed change of ATF (automatic transmission fluid), usage of a poor-quality ATF and disregard of the main rules of operation by the driver.

Informative videos about problems that may occur in transmission valve bodies

Reasons of valve body malfunctions includes the following:

- clogging of valves, spools, and plungers with mud that prevents springs from moving valves and hinders solenoids from opening valves (proper cleaning solves this problem)

- metal particles scratch surfaces of channels, clutch components, and spools that results in their wear-out and oil leakages

- wear of spare parts: weak springs, damaged paper gaskets or worn metal gaskets, balls and filters clogged with mud, hardened rubber rings (almost all of these problems are solved by replacement of damaged transmission parts)

- fast accelerations lead to wear-out of friction clutches

- failure of solenoids (contacts oxidation)

- issues with sensors (overheating, clogging with magnetized dust from ATF, burning out); usually car transmission repair specialists solve this problem by cleaning or replacement of sensors

- wiring failure, short-circuit, broken wire; usually such issues are easily solved by the wiring replacement avoiding expensive and time-consuming repair processes

- electric board failure which is usually diagnosed according to fault codes; most of electric boards are successfully repaired by replacement of burnt elements (usually it is one of the sensors)

- contamination or wear of the valve body itself, wear of spare parts – valve body gaskets, rubber seals, filters; the most problems are caused by wear or contaminated oil, mainly due to worn out clutches and glue layer which sticks together friction linings and a steel frame

- structural integrity issues caused by hardened rubber, which leads to wrong distribution of oil

- frequent transmission overheating

From year to year, valve bodies become more and more complicated. Nowadays, valve body design includes such new spare parts as paper gaskets with integrated liter screen, filter-nets for channels and solenoids, plastic valves and much more.

Valve body repair

The repair of modern valve bodies usually includes the sequence of following procedures:

- collection of and analysis of computer data (fault codes), diagnostics (vacuum testing)

- valve body teardown/removal

- valve body cleaning/washing

- inspection and performance measurement of solenoid valves

- detection of parts to be replaced

- rebuilding of control valves

- assembly and valve body calibration

- vacuum testing

- installation

Videos about valve body repair

The teardown of the valve body and following cleaning/washing, spare parts replacement and assembly are considered to be a scheduled set of operations. Transmission specialists recommend auto owners to perform these operations together with the torque converter repair and replacement of the filter. It is also advised to clean the valve body with a special cleaning liquid. In addition, transmission repair specialists usually change the sealing gasket before the valve body assembly. Car owners may get off lightly if the problem is detected in the early stage. In this case, transmission specialists limit themselves to cleaning and washing of the valve body, replace its spare parts (and solenoids if needed). Another trivial problem is the failure of wiring which applies power to solenoids and sensors. The solution of this problem usually takes just several minutes and comes cheap.

In most cases, solenoids with a low-level contamination are rebuilt. After rebuilding solenoids can operate for a long time. Strongly damaged solenoids should be replaced, because their rebuilding will be more expensive than buying new ones. To prolong the service life of automatic transmissions and valve bodies experts recommend to perform transmission fluid change and wash the valve body in due time. Solenoids should be replaced after running 80-150 thousand kilometers.

The most problematic valve bodies

The list of valve bodies with issues related to the electronic components (electronic plate/Mechatronic) includes:

• ZF6HP19/21-26 with Mechatronic issues. Usually car owners order Mechatronic rebuilding. ZF company performs rebuilding of these problematic plates.

• Often problems occur in the conductor plate of the automatic transmission 722.9 installed in Mercedes cars. This problem is related to overheating and violation of characteristics (temperature-resistance) of some plate elements.

• Jatco RE5R05A . Transmission specialists have to deal with burnt valve body parts. The problem is related to voltage swings when jump starting a car or switching off accumulator terminals in the started car.

The most frequently replaced valve bodies are the following:

1)TF60SN /09G is considered to be one of the most frequently replaced valve bodies. In most cases problems occur because of improper operation of worn solenoids. Previously transmission specialists simply replaced the whole valve body, but now they replace faulty solenoids. The replacement of faulty solenoids helps to prolong the service life of the transmission for several years when the problem is detected in early stages.

2) AW55-50 is another automatic transmission with valve body issues. Recently repair specialists have started to limit themselves to replacement of solenoids instead of the whole valve body replacement.

3)U660E U660E has the same problems with the valve body as AW55-50, namely solenoids. But if the during testing specialists detect many leakages, it is required to replace the whole valve body.

4) U150F and TF80-SC are also considered to be automatic transmissions with a problematic valve body. Usually valve bodies are replaced when channels are worn out by hot and contaminated transmission oil from the torque converter.

Valve body testing equipment

In case of any problems related to valve body, transmission specialists have to perform diagnostics with the aim to detect the particular source of malfunction and only after that start any repair procedures.

Vacuum testing is the simplest method to detect valve body failures before the repair and to ensure the repair quality before the valve body assembly. Vacuum testing tools are not complicated and inexpensive devices, but auto transmission repair specialists consider this tool to be indispensable in professional activities. The vacuum testing allows specialists to assess the condition of valves (plungers) in the valve body. Worn valves may cause malfunctioning, reduced efficiency or automatic transmission breakdown.

We will review vacuum testing products produced by Sonnax and Cottingham Engineering:

1) Sonnax offers the vacuum tester, which is very helpful in time saving and efficient leakage testing of the valve body channels. Whether you are checking a problematic valve body or examining the rebuilding procedure quality, this vacuum testing kit will be a must-have tool. Features of this device include top-quality brass needle-point valves and an embedded test orifice for uncomplicated calibration .

Sonnax tester includes:

• Vacuum stand
• Test plate
• Quick-detachable connections
• Various connector
• Hoses

2) Cottingham Engineering, in turn, offers a user-friendly bench tool for vacuum testing with attached user’s manual.

This is a useful tool for data-gathering related to the valve body condition. The principle of operation is very simple: adjust the vacuum and record leakages caused by worn or ill-fitting valves. This is a mandatory tool for any workshop wishing to restore valve bodies back to original specification.

Learn how the vacuum testing is performed

Nowadays when automatic transmissions are becoming more and more advanced, transmission repair specialists cannot use only simple tools (like vacuum tester) to provide high quality service in repair of valve bodies. Therefore, specialized companies put a lot of efforts to develop sophisticated equipment for valve body testing. We will review several tools for valve bodies repair offered by SuperFlow, Cottingham Engineering, and Raytech.

HT-VBT Deluxe

HT-VBT Deluxe unit is a great piece of equipment for workshops with different ranges of business. With this technical solution repair specialists get an automatically-controlled electronic pressure regulation, allowing recurring ATF supply to the valve body, as well as all main characteristics of competitive products, which are available on the market. This unit was developed with an improved heating-up controller and double temperature check, so it can withstand high temperatures during the testing process. It also has more powerful pressure pump. HT-VBT Deluxe is equipped with additional work surfaces and devices for proper organization of the workspace. Engineers of Cottingham Engineering constantly develop new test plates and design effective test scenarios, which help to perform detailed diagnostics and compare testing results with master data.

Axiline VBT 8000

Nowadays Axiline VBT 8000 is considered to be one of the most advanced valve body testers, which now also includes Mechatronic valve bodies. So far, there is a limited range of Mechatronic valve bodies which can be tested with this unit. VBT 8000 has an entirely new design and sophisticated software and data-gathering packages also give it the capacity to test transmission solenoids. However, this unit may seem quite complicated in usage for inexperienced specialists. By simulating the most severe driving conditions using the same regulated pressure and heated ATF as seen under normal operating conditions, Axiline tester precisely and effectively confirms your rebuild. SuperFlow engineers constantly develop new adapter plates for VBT 8000 to test a wider range of valve bodies.

Transmission Test Equipment 220V, AC, 4KW Valvebody Tester

The Chinese company RayTech offers its own solution for testing valve bodies. This system has an automatic control program, which performs complicated tests in just a few minutes. The process of testing is monitored by the computer on a real time basis. The system analyzes all data related to the valve body performance during testing, compares this information with master data, detects all deviations, and forms the report. Thanks to this solution transmission repair specialists can detect all valve body malfunctions and solve these problems in a prompt manner.

All in all, valve body fully deserves the name of the automatic transmission “brain”. It is a complex technical element that performs the conversion of the electric signal from the transmission control module into ATF pressure. ATF, in its turn, ensures interaction between transmission actuating elements. Generally, the valve body repair requires high qualification from repair specialists and usage of modern equipment, therefore cutting-edge testing solutions mentioned above serve to workshops as sophisticated tools for diagnostics of such a complex gearbox component as the valve body. Well-timed visits to professional workshops help not only to prolong the valve body service life, but also may postpone the necessity of the automatic transmission overhaul. The neglect of valve body problems may lead to the necessity to restore the whole transmission.