Technically Speaking

• Subject: Checkballs used as plugs to seal circuits
• Unit: Mercedes 722.6, 722.8, 722.9
• Essential Reading: Rebuilder, Diagnostician
• Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

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If you have had the opportunity to work on a 62TE transmission, you may have noticed nine checkballs in tapered pockets that are held into place with C clips (Figure 1). In our seminars we explained that these balls are used during an assembly-line check with a special tool that pressurizes their respective circuits. Once the tool is removed these balls become plugs. Apparently this procedure was more economical when compared with the cost of providing typical pressure taps. But what this means to you is that these balls must be checked to ensure that they are in their location and that they are sealing. Otherwise you could be fighting a variety of different complaints.

Interesting enough, Mercedes is no exception to this type of assembly-line check. Remember the days when it was DaimlerChrysler? Could be the reason for the similarity. Take the 722.9 transmission, for example. There are 14 steel checkballs in the lower portion of the valve body (Figure 2).

Looking at them carefully reveals how these balls sit deep in their pockets (Figure 3). The opposite sides of these balls are port openings that face the pan (Figure 4).

It becomes quite obvious that these balls are not being used in the hydraulic activity of the valve body. There is nothing to move them other than gravity and fluid pressure pushing them down to seal off the port opening facing the pan. The reason for this is that these balls are similar to the ones in the 62TE in that a special tool enters these port areas of the valve body to conduct a pressure check of their respective circuits. When the check is done these balls are to seal these ports.

The difference is that there are no C clips holding these balls in place. They rely on just gravity and pressure to do the job. Some valve bodies use little springs on top of each ball to ensure that they are seated (Figure 5).

Either way, it is imperative that these balls be in their locations and that they seal; otherwise, you could have any variety of problems depending on which ball or balls are leaking or missing. Figure 6 identifies each ball’s respective circuits that they seal.

Keeping your eye on the ball is a must with these units as well as with the 722.6 transmission here in the States and with the 722.8 continuously variable transmission overseas.