Chronic Valve Body Wear

Transcription

1 Chronic Valve Body Wear by Larry Frash Every penny I ve earned in my life has been from the automotive industry. For that, I am thankful. If the manufacturers made a perfect vehicle, all we could hope for is to be somewhere in the auto-body repair industry. People will never stop crashing cars! But let s face it; there are certain transmissions that put food on our tables every day. We all know which ones I m talking about. But chronic valve body wear is where I draw the line between thanking the engineers, and blaming them. I think most of us already know a handful of transmissions that, with more than 50,000 miles on them, will have a worn valve body! I know that someday I ll read an extended warranty, and at the bottom of the page there will be a notation saying: To honor this warranty, the spare valve body (located in the trunk) must have been installed at 45,000 miles. Come on ref throw the damn flag! I m okay with broken planetary gears and stripped drive shells. Driver abuse causes a lot of this. But when a car with 50,000 miles comes into a shop, setting a code P1870 due to a worn valve body, there s something wrong at the engineering level! With that said, let s discuss some theories of why certain valve bodies wear in certain areas and others don t. Theories may seem useless when trying to understand and/or solve problems, but keep in mind that some of Einstein s theories weren t proven for years after his death. The intention of To this article is to open your eyes to a problem that is plaguing our industry, and point out the common valve bore types that wear the most. For something to wear, it must experience friction, which needs motion. The more a valve moves in its bore, the more chance it has to wear. This is why shift-valves rarely wear, and regulating valve bores do so, often. But why are some regulator valves prone to wear and others aren t? To begin, let s review how two basic types of regulator valves work. Mainline Regulator Valves For this example, we will assume the regulator spring is calibrated for a desired mainline pressure of a constant 70 psi. If pump volume cannot keep up To Figure 1 with this demand, the regulator valve would be in what we ll call the stage one position (figure 1). In this position, the regulator valve is in the deepest part of the bore, supplying oil to the mainline circuit only. You ll also notice the valve is not supplying oil to the converter/lube circuit. Once pump volume is high enough, and mainline pressure exceeds the desired 70 psi, the balance oil pushes the valve into what we ll call the stage two position (figure 2). As the valve moves into this position, pump volume is supplied to the torque converter/lube circuit. This use of pump volume will reduce mainline pressure. If this is not enough to reduce mainline pressure to the desired 70 psi, balance oil will push the valve into what we ll call the stage three position 24 GEARS April 2004

2 COMPLAINT: Also: Shift timing concerns Throttle buzz Poor kickdown Late 2-3 upshifts Oversensitive 3-2 downshifts CAUSE: Original equipment downshifts prematurely and takes engine out of the torque band. CORRECTION: This hardened steel valve and spring reduces throttle sensitivity and lowers downshift points. LATE 3-2 DOWNSHIFT IN DIESEL & TOWING APPLICATIONS Valve Body HEAVY DUTY THROTTLE VALVE KIT Balance Spring Heavy Duty Throttle Valve Alternative Throttle Valve Spring 42/46/47RH/RE, A904-A727 Shims Sleeve Also available from Sonnax : RENAULT DPO P/N: PUMP BUSHING Part No HDK COMPLAINT: Also: No forward or reverse Burned low/reverse clutch Harsh 2-1 downshifts CAUSE: Grooves worn into aluminum case by steel clutch plate lugs interrupt smooth clutch apply/release. CORRECTION: Thin hardened spring steel inserts fit into the damaged case channels. The steel plates included with the kit have unique lugs that are narrower than OE to allow clearance at the installed inserts. Part No K STEEL PLATE LUGS WEAR GROOVES IN CASE CLUTCH CHANNELS LOW-REVERSE CLUTCH CHANNEL INSERT KIT Friction Clutch Plates Insert Ring Channel Inserts Throttle Plunger Chrysler A604/A606 Steel Clutch Plates 4R44E, 4R55E, A4LD P/N: 56412RK FRONT PLANETARY REBUILD KIT FORD SOLENOIDS MULTIPLE YEARS & APPLICATIONS P/NS: 56842B-01, , , See your nearest Transmission Specialties distributor & ask for Sonnax quality engineered products. VISIT OUR WEBSITE FOR SONNAX REAMERS & OTHER TOOLS. Automatic Drive P.O. Box 440 Bellows Falls, VT USA 802/ / fax: 802/ info@sonnax.com Sonnax

3 Chronic Valve Body Wear To To To To Figure 2 Figure 3 Accumulator Pressure Exhaust Line Pressure Accumulator Pressure Exhaust Line Pressure To Accumulator To Accumulator Figure 4 Figure 5 (figure 3). In this position, the valve will open an exhaust circuit back to the pump intake. This will essentially create a large enough leak to reduce mainline to the desired 70 psi. In a perfect world, with non-varying pump volumes and demands, this regulator valve would tend to find a position somewhere between stage one and stage three and simply stay there. However, as we all know, this couldn t be further from reality. Varying engine RPM, and constant mainline pressure adjustments by the computer or throttle cable keep this valve very busy. Other Regulator Valves For this example we ll use a simple accumulator regulator valve with a desired pressure of 30 psi. Unlike the mainline regulator, we don t want to exhaust pump volume to control a separate circuit like accumulator pressure. If we did, mainline pressure would also drop to 30 psi. So this type of regulator valve works a little differently. In the stage one position, the valve is deepest in the bore, supplying mainline to the accumulator circuit (figure 4). Once the accumulator pressure rises above the desired 30 psi, balance oil will move the valve into the stage two position (figure 5). In this position, the valve cuts Accumulator Pressure To Accumulator off the mainline pressure that supplies the accumulator circuit. Cutting off this feed will lower the accumulator pressure. Just past the stage two position is the stage three position (figure 6). Here, the valve opens an exhaust to leak accumulator oil from the regulated circuit. The valve will float back and forth to maintain the desired pressure. Exhaust Line Pressure Figure 6 Boosting Regulating Valves Many regulating valves are used in such a way that they provide varying pressure. For an example of this, we can simply add a boost valve to our mainline regulator valve (figure 7). As throttle pressure or EPC pressure rises to the boost valve, the boost valve increases pressure on the spring side of 26 GEARS April 2004

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5 Chronic Valve Body Wear the regulator valve. This makes it harder for the balance oil to move the regulator valve, and is how line rise is created. Throttle Pressure On a 700-R4, the mainline regulator boost valve is controlled by throttle pressure. As the throttle cable is pulled, the TV plunger compresses the spring, making throttle pressure rise. Because throttle pressure rise is obtained by mechanically compressing a spring, the pressure will smoothly rise with no pulses in fluid pressure. Electronic Pressure Control When a computer controls the boost pressure, it does so by pulsing a solenoid on and off at a very fast speed, called a pulse-width modulated signal. The frequency by which this happens is measured in hertz (pulses per second). This can be anywhere between 20 and 900 hertz, depending on the year, make, model and application. The main thing to keep in mind is that the computer doesn t change the frequency to change pressure. It changes the duty cycle, which is the percentage of time the solenoid is on, versus the time it is off. Most EPC solenoids are calibrated to use 50%-60% duty-cycle for minimum pressure, and 0%-10 % for maximum pressure. However, for ease of explanation, we ll use the following hypothetical example. Let s say you supplied battery-voltage directly to the EPC solenoid making EPC pressure zero psi and if you turned the solenoid off, EPC pressure would be 100 psi. In this example, if you turned the solenoid on for exactly 1/10 th of a second, and off for exactly 1/10 th of a second, and repeated this over and over again, EPC pressure would average 50 psi. This is because it would be on for 50% of the time, and off for 50% of the time. If the solenoid was on for 25% of the time and off 75% of the time, EPC pressure would average 75 psi. However, unlike the throttle valve in the 700-R4, the constant pulsing of the EPC solenoid causes the EPC pressure to oscillate at the frequency that the computer is using to operate the solenoid. Although it is next to impossible to measure these pressure pulses, they do EPC Pressure EPC Pressure To Converter/ Lube exist. But what does this have to do with valve bore wear? These pressure pulses, if large enough, can make the related valves oscillate. For example, if EPC pressure is oscillating, the boost valve being controlled by the EPC pressure will try to oscillate. Remember, the more a valve moves in its bore, the more chance it has to wear. Which causes more damage low frequencies or high frequencies? Low frequencies tend to cause fewer but larger pulses, while higher frequencies tend to cause more but smaller pulses. Because larger pulses in pressure tend to move valves easier than small pulses, the lower frequencies cause more damage. In fact, newer vehicles are using much higher frequencies to control solenoids than earlier models. Maybe we re on to something. All pulse-width modulated solenoids work like the example cited above. However, some supply maximum pressure when turned off, while others supply minimum pressure when turned off. For example, many PWM lockup solenoids supply minimum pressure when turned off, so that lockup is disabled in the event of a power failure. Valve Material Many of the newer valve bodies are using hardcoat anodized aluminum valves. The valves themselves are very durable. But does the material that these valves are made of cause the bores to wear? Well, I m sorry to X To Figure 7 say we just don t know yet. However, what we do know is that these valves are extremely light in weight. Logically, lightweight valves are more easily moved than heavier ones. This means that the pressure pulses can oscillate the aluminum valves easier than the steel valves. Valve Support Some valves are too short, and wear due to a lack of support in the casting. A good example of this is the isolator valve located in the bottom of the 4L60E TCC regulator bore. This poor valve is controlled by a PWM solenoid, is made of the lightweight hardcoat anodized aluminum material, and has very little support. And wouldn t you know it it wears a bunch! Valves To Look At Whether the valve body wear is being caused by the electronics, valve material and weight, or just poor design, the fact remains that there are a lot of valve bodies from all makes that are wearing faster than they should. The important thing to remember is to always remove the valves from the valve body and inspect any valve bore that is subject to wear. Whether you install an aftermarket repair kit, or buy a new valve body, it s always best to find the problem before the customer is given the final estimate. It means the difference between them paying for it, or you paying for it. 28 GEARS April 2004

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