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The Importance of a Positive Seal: 722.6 Issues

There are at least two major issues that are caused by the lack of a positive seal in 722.6 converters. One issue is the shutter on TCC apply and the other is insufficient or no cooler flow. These seemingly unrelated complaints share a common cause, but the cause-and-effect relationships are quite different.

The Importance of a Positive Seal: 722.6 Issues

Leeward Tech

Author: Ed Lee, Contributing Editor
Subject Matter: 722.6 converters
Issue: Lack of positive seal

Leeward Tech

  • Author: Ed Lee, Contributing Editor
  • Subject Matter: 722.6 converters
  • Issue: Lack of positive seal

Part 2 of at least two parts

There are at least two major issues that are caused by the lack of a positive seal in 722.6 converters. One issue is the shutter on TCC apply and the other is insufficient or no cooler flow. These seemingly unrelated complaints share a common cause, but the cause-and-effect relationships are quite different.

The TCC apply shutter happens when the clamping force required to hold the clutch is less than adequate. This is caused by a leak between the input/turbine shaft and the aluminum sleeve in the cover of the converter. The reason for the leak is the lack of a positive seal. In the TCC apply mode, TCC apply oil travels down the input shaft, exits the shaft into the cavity in the aluminum sleeve between the seal and the interference fit (figures 1 and 2).

From this cavity the oil travels through the three 0.160” holes in the sleeve and ends up under the TCC apply piston, moving it to apply the clutches (Figure 3).

When the converter is new this system works well, but as the converter ages, the interference fit becomes less effective.

A positive seal can be added to the aluminum sleeve by machining a cavity in the sleeve (Figure 4).

There are two Mitsubishi seals that will work for this application (part numbers MT-O-5V/TO25-5 and MT-O-6V) but the MT-O-6V works best because it is a tighter fit on the shaft.

When you are addressing the leak at the interference fit, you need to consider other issues that may be caused by the wear in the bore.

Since there is no bushing in the end of the stator support, the interference fit in the aluminum sleeve is the only area supporting the end of the input shaft. The area in the aluminum sleeve where the OE seal lives is larger in diameter and provides no support. It is important to hold this end of the input shaft on a proper center line to give longevity to the planetary gear set at the other end of the shaft and to the bearing that lives between the input and output shafts. Some shops are adding a bushing to this area for support (Figure 5).

The issue of the lack of cooler flow is not as straightforward as the TCC apply shutter issue. Many shops have not recognized this issue. If you are not dealing with an overheating problem, you are not even looking in this area. The problem was exposed because most dyno tests have a pass/fail parameter for cooler flow. For the Sprinter transmissions the pass/fail for cooler flow is between 2.5 GPM and 3.5 GPM. On some converters cooler flow was a low as zero.

The cause:

No positive seal between the input shaft and the aluminum sleeve.

To understand how a leak at the interference fit can cause a lack of cooler flow, you need to think about the TCC apply circuit. This converter has a three-path circuit, and more important, it is not like the typical three-path circuit used in the front-wheel-drive Fords and Hondas. The Fords and Hondas rely on a bypass valve in the third circuit to control lockup. The 722.6 three-path circuit, on the other hand, uses a valve similar to the “switch valve” in a rear-wheel-drive Chrysler transmission to regulate lockup. This valve is called the “lockup control valve,” and its functions are similar to the Chrysler switch valve. It directs oil to the TCC piston and also moves to vent that oil to exhaust.

The difference in the two valves is that in the 722.6 three-path converter, when the oil is vented to exhaust, it releases the TCC piston; and in the two-path converters (like the rear-wheel-drive Chryslers), when the oil is vented to exhaust, it allows lockup to occur.

The in-and-out (two path) oil in the 722.6 converters lives on the turbine/stator/impeller side of the interference fit in the aluminum sleeve. The TCC apply/release circuit (third circuit) lives on the other side of the interference fit. The big clue to solving the cooler flow problem was that the cooler flow was almost normal when the converter was in the TCC apply mode, but would quickly drop off when TCC was released. The cooler flow that was normally captive in the two-path side of the converter was allowed to escape through the TCC apply circuit that was open to exhaust in the TCC release mode.

Adding the positive seal to the aluminum sleeve restored cooler flow on 100% of the converters, even though it looks like the seal is facing the wrong direction. When you are modifying the aluminum sleeve, it is also necessary to block the vent passage (Figure 6).

This is another pathway to leak if left open.

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