Intro to the Hyundai/Kia 6-speed transmission

April 29, 2014
Hyundai has been quite forthcoming with providing technical data for its 6-speed transmission — much of which is required should the need arise to diagnose one of them.
Figure 1
Figure 2
Figure 3

Hyundai has been quite forthcoming with providing technical data for its 6-speed transmission (Figure 1) — much of which is required should the need arise to diagnose one of them. This transmission is used in both Hyundai and Kia vehicles as far back as 2009 here in the United States. 

On the transmission there is a tag riveted to the case with the vehicle identification number on it. Alongside this tag, etched into the case, is a transmission number (Figure 2). For a guide to all the versions of this tranmission, and what the different VINs signify, visit www.motorage.com/hyundaitrans.

With a quick look at the cutaway of this transmission in Figure 3, you can see that this 6-speed is a compact unit. It uses a triple planetary setup with a low one-way clutch device, two driving clutches and three brake clutches. Put this together with the component application chart shown in Figure 4, along with the solenoid application chart in Figure 5, and you yourself have quite a bit of information to do a considerable amount of diagnostics.

One of the first things I like to look for in a clutch and brake component application chart is not just what is on and off for each gear, but which shifts are synchronous and non-synchronous.

First gear

Let’s begin with taking a look at first gear. You will notice that the Low/Reverse (L/R) clutch is applied as indicated by the solid circle. The same is true with the Underdrive (UD) clutch and the one-way-clutch device. You will also notice that with the L/R clutch there is an arrow to the left pointing to an “X,” while the opposite is seen with the low one-way-clutch (OWC) device.

What this tells us is that the L/R clutch will be released before the shift into second takes place. When it does, the OWC device will hold stationary the same part of the planetary system the clutch was holding. In short, when the L/R clutch is applied, the low OWC device is ineffective until the L/R clutch is released. This OWC will need to hold until a shift into second takes place. The UD clutch remains applied so all that needs to take place is to add the 2/6 clutch to make the 1-2 up-shift. The OWC simply freewheels at this point and is no longer a part of the powerflow. This system makes the 1-2 up-shift and the 2-1 downshift a non-synchronous shift.

Figure 6

A shift like this is only possible because of the electronic controls that we have in automatic transmissions these past several years. Before this type of electronic control, it was not possible to apply and release a clutch in the same gear. To have a clutch apply for the initial launch of the vehicle in first gear, only to turn it off at 5 mph (or 150 rpm of the output shaft), is one of the many byproducts of electronic control. But this introduces a different type of concern when part of this type of shift is compromised.

Back in the early days when a low OWC device failed, you would not be able to launch the vehicle in the normal drive range. You had to select manual low for the L/R clutch (or band) to apply which took over the OWC’s job. The vehicle would then be able to move but should you shift the selector lever out of manual low before the 1-2 shift occurs, it would immediately dump to neutral.

With electronic controls keeping the L/R clutch applied in regular drive position, as soon as it releases before the 1-2 shift takes place, if the OWC is bad, it, too, will dump to neutral immediately.

There are several transmissions that use this type of non-synchronous 1-2, 2-1 shift. Dodge vehicles with the 68RFE transmissions is one such example. It is notorious for the low OWC to fail, dumping the transmission into neutral soon after launch. The A6 OWC design being a spring and roller (Figure 6) is more reliable of a device than an element sprag type being used in the 68RFE transmission.

Higher gears

Figure 7
Figure 8
Figure 9

The 4 shifts remaining, the 2-3, the 3-4, the 4-5 and the 5-6 are all synchronous shifts. The timing involved to release the 2/6 clutch while the 3-5-R clutch applies to achieve a smooth 2-3 shift is critical. The same is true of the others. If the release-apply time is too long, the shift is harsh. If it’s too loose, it slips.

This timing takes into account the correct clutch tolerances — it remains within range for the computer to be able to adapt. Once it exceeds programmed tolerances, shift quality will be affected.

Piston seals, sealing rings and gear train endplay also play a role in the shift quality. Solenoids and their respective valves in the valve body are yet another factor.

As briefly mentioned in a previous newsletter called “The Triple Threat,” in some cases even cooler pressure working between the apply piston and the balance piston is also an important factor in shift quality. Bushing wear or pressure regulator valve bore wear can cause cooler pressure to be compromised, affecting the shift quality of the transmission.

Typically, clutch assemblies that have balance pistons are the driving (spinning) clutches, such as the 3-5-R (Figure 7) and Overdrive clutch assemblies (Figure 8) in this transmission. In most cases, these balance pistons are quickly identifiable. They are designed to hold centrifugal head oil, which is why only the outer perimeter has a molded seal on it (Figure 9).

Making the diagnosis

Figure 10
Figure 11
Figure 12
Figure 13

By just this brief explanation, diagnosing flared shifts or harsh shifts can be somewhat challenging. With a considerable number of variables involved, where does one begin?

In general, this usually depends on the scenario at hand. If the vehicle has come to the shop with shifting issues and there was no prior work performed on the vehicle, chances are there will be internal problems. This is especially true if the fluid color and smell indicate that some burning of the clutches has taken place.

If fluid inspection does not indicate an internal problem, resetting shift adapts might be considered. The question becomes, “Why would it suddenly need to be reset?” This is a good question. In fact, to know some of the reasons that can cause adapts go out of range is part of the diagnostic process.

We have seen a variety of causes for this dilemma: Incorrect engine load calculations, low fluid levels or compromised fluid filters and seals, a faulty battery and/or charging system voltage, bad TCM/PCM power supply or grounds, as well as both a defective computer or one needing a program update from the manufacturer.

Of course, if there were prior repairs or lengthy battery disconnects, this could be another reason for the need to reset shift adapts. But if all arrows point to the transmission as having problems causing the shift concerns, one place to start can be with some pressure testing (Figures 10 to 13). Because this can be a time-consuming process, this step is usually bypassed. But if one chooses to do some testing, the best way to do this is with transducers.

Figure 14
Figure 15

Transducers will allow you to graph out the clutch coming off and the clutch coming on. Depending on engine load and temperature, the overlap can take place between 30 to 50 psi for approximately 0.5 seconds — at which time the off-going clutch rapidly ramps down to 0 while the on-coming clutch quickly ramps high.

Admittedly, consistent pressure testing and graph reading will be required to become keen with interpreting the data. The results could point toward solenoid issues, valve bore wear, clutch clearance issues or a combination of failures. Characteristically, however, pressure testing is bypassed and the valve body or transmission is pulled for inspection (Figure 14).

Figure 15 identifies all the solenoids on the valve body, as well as the clutch regulating valves. You will notice that it appears to be a regulating solenoid for each of the clutch assemblies, with the exception of the L/R clutch.

What basically is occurring here is that the manual valve supplies regulated line pressure to the 35R directional control valve. After it passes through this valve, it goes to the L/R directional control valve in two places. This action strokes the valve and supplies ramp on regulated line pressure to the L/R clutches.

Solenoid concerns

Figure 4
Figure 5

The 35R solenoid and Shift Solenoid B can influence the apply of the L/R clutch, while simultaneously the 35R solenoid controls the apply of the 35R clutch. Shift Solenoid B can also be used to prohibit reverse by turning off, which will close the 35R directional control valve — blocking regulated line pressure from the manual valve to the L/R directional control valve.

A little about the operation of the solenoids: Both On/Off shift solenoids A and B receive pressure between the two O-rings on the snout of the solenoids. When the solenoid is off, the pressure is open to a metered exhaust out the base of the solenoid. When it is turned on, this pressure is then directed to their respective valves out of the tip of the solenoid.

These two solenoids measured 10.5 ohms at room temperature (approximately 72°F). The six remaining Variable Force (VF) Solenoids all measured 5.1 ohms at the same temperature. Factory specifies 10 to 11 ohms for Shift Solenoids A and B, and the six VF Solenoids at 5.1 plus or minus 0.3 ohms.

Four of these six VF Solenoids are Normally High (NH), while the other two are Normally Low (NL). The Pressure Control, UD, 35R and OD solenoids are all NH solenoids, which means when they are fully off, they supply maximum pressure to their respective valves. By contrast, the TCC and 26 NL solenoids need to pulse on to send pressure to their respective valves.

This makes comparing the Component Application Chart in Figure 4 with the Solenoid Application Chart in Figure 5 more sensible. Take, for example, the Underdrive Clutch and Solenoid. When the solenoid is off, the clutch is on; when the solenoid is on, the clutch is off. Yet when the 26 clutch needs to be on, so does the solenoid.

Just this simple understanding goes a long way in diagnosing shift concerns. If there is a delayed engagement into drive with a flare 6-4, 5-3 kickdown, the UD solenoid, UD shift valve group, accumulator and UD clutch system (rings, seals, piston) are all suspect. And once again, depending on when this problem began, it could be something as simple as a lazy solenoid.

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