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Courtesy of Brakes & Front End, by Bob Warnke
All transmission models have unique problems that are common to that model; The JATCO CVT unit is no exception. Technicians face an uphill battle when it comes to diagnosing and repairing a CVT if they don’t have the right information. Knowing what the common problems are and understanding the options available to isolate and fix the problems is the key to a successful repair.
First, Do No Harm
Without the right information, we end up making assumptions – often the wrong ones. Generally, when unfamiliar with the transmission, we start by looking for service instructions in newsletters and websites. Sometimes we read a tip and assume that the information matches our complaint. If we are action-oriented and short on time, we may react too quickly and assume it is best to take the unit out for repair. Too often, though, assumptions take the long way – leading to the wrong conclusions.
The following is an example of the “runaway” assumption:
- After towing the pan for routine maintenance service on a unit with 40,000 miles of range, technicians found the magnets heavily loaded when compared to typical automatics. Looks like the unit is headed for failure.
- After cleaning the magnets and refilling the unit with the correct CVT fluid, the car was trialled around the block. Working fine and ready to ship.
- Two days after picking up the car, the owner came back claiming the vehicle had excessive noise and seemed to be slipping. Because of the material previously found in magnets, the decision was made to withdraw the transmission.
Wait, action-oriented enthusiast. Not too fast! If you want to be successful with CVT, you have to know why this assumption is wrong. Once you have that information, you can start learning about some common CVT problems and their causes, all without removing the unit from the vehicle.
The first wrong assumption has to do with magnets. A normal amount of magnetic fuzz in a CVT checked at 40,000 to 50,000 miles. Push-belt links create frets where they contact the sheave/pulley surface, which is mostly generated during break-in. However, given this material is normal, consider that most of that iron fuzz has circulated throughout the valve body. It has been embedded into the solenoid and attaches to the speed sensor – which are all electromagnets – while also rubbing the aluminum valve orifice. That is, fluff is normal, but also valve bore wear with low mileage.
The second false assumption is that a test drive of the vehicle around the block after fluid exchange is sufficient. These units use a thermal element in water-to-oil (WTO) cooling. The fluid must reach approximately 150°F for the element to open and allow oil to flow into the cooler. Once open, the air is purged, keeping the sump level low. Low fluid causes chain slip and noise on acceleration. Driving it in these low fluid conditions will eventually damage the unit and require a tow.
The third mistaken assumption is that the transmission needs to be disconnected. As we just saw, it would be a mistake to commit to pulling the unit before verifying the correct fluid level. There’s no dipstick, and guessing what’s draining from the pan isn’t enough. You can buy a dipstick from Chrysler or an aftermarket source, or you can make your own. The transmission fill tube has an internal stop at the bottom. You can make a dipstick and mark in 10mm increments starting at the bottom and working your way up. At 75°F, the minimum/maximum liquid level should be 26mm to 38mm. At 180° F, the minimum/maximum liquid level should be 38mm to 46mm.
Isolate Common Problems
We’ve just identified a few non-issues, but what if we run into actual issues? Let’s look at some information that will help isolate the problem once it’s presented in the store. Charts and diagrams (Figure 1-5) shows the pressure specifications, tap locations, and flow test information you need for diagnosis.
As you can see, there’s some very high pressure here compared to typical automation. For pressure testing, use a gauge with a minimum of 1,000 psi (7,000 kPa). A typical JATCO port adapter is required. If you don’t have one, make one by first drilling a center hole into the casing plug, then soldering it into the 1/8″ pipe.
It is very easy to identify the location of the pressure tap (Figure 6). Most of the fill valve and plug face forward, towards the radiator and just below the input speed sensor. They form a four-point circle, with the main pulley pressure valve in the center. The reverse brake cock is near the shifting shaft on top and the secondary pulley cock is on the firewall side. Note: this configuration is specific to JF011E; different tap locations on other CVT units. Consult available reference material for tap locations on other models.
Let’s see how we can use this information to isolate some common CVT problems. Bear in mind that, due to high pressure, it is recommended that you hang the gauge outside the vehicle rather than inside.
In your attempt to isolate this issue, be aware that the converter clutch does not have enhanced applicability. It locks depending on engine speed by about 1500 on acceleration. The TCC does not open on deceleration to about 10 mph. In contrast, a regular automatic usually engages after a 1-2/2-3 gearshift and has controlled slippage, which is necessary in such units for ease of driving and fuel efficiency.
The following are the most common complaints of CVT units and areas to investigate:
- Chatter, noise or judder on acceleration
- Check line pressure, TCC release, forward coupling and primary/secondary pulley pressure, and bearings.
- Bearing failure is widespread. Usually with bearing failure, fluid level and pressure will be fine, but a whining sound will be heard on acceleration.
To determine which bearing is making noise, drive at a constant speed (where the noise is strongest) and manually switch to a lower ratio — this increases engine speed. If the noise increases with engine speed, the main pulley bearing has failed. If the noise remains constant with increasing rpm, the secondary or final drive bearing is to blame. Sometimes, bearing noise can be accompanied by low secondary pulley pressure, because if the bearing fails, the shaft can derail and damage the pulley input seal. Replacement bearings are readily available on the aftermarket.
- RPM spikes/tripping at idle, stalling on start: Check forward clutch pressure. Check coolant flow and/or TCC apply/remove pressure.
- No TCC applied or rpm change at 1500 rpm: Check TCC application and release pressure.
- Hydraulic noise at idle: Check TCC discharge pressure.
When encountering low pressure, focus your inspection on the valve body. For any out-of-spec pressure series, perform a vacuum test at the associated orifice. For example, if you have low line pressure, you would move to the main pressure regulator valve/orifice vacuum test. If you have low primary pulley pressure, test the control valve/primary pulley orifice for vacuum, etc. If all pressures are low, suspect the pump flow control valve. In fact, these valves are notoriously worn on most units; it would be better to replace it with an oversized version at each repair to prevent any possible return of warranty. A failed flow control valve will also often cause codes to be set such as ratios, pressure sensors and/or solenoid codes “A” or “B”.
As you can see, the available information and test tools can be used to diagnose many CVT problems without removing the transmission. When armed with solid service information, an understanding of common problems and how to identify their causes, CVT can be a great painless source of income for any transmission shop.
Post Transmission – CVT appeared for the first time on Import Cars.
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