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If the owner of a Mercedes-Benz vehicle equipped with the 7G-Tronic (NAG2) automatic transmission complains of an uncomfortable/rough 1-2, 3-2 and 2-1 gearshift, this may be due to the specific gear not being fully adapted or there could also be a mechanical cause as well.

1. Reproduce the complaint and identify the affected shifts using Star Diagnosis.

2. Print out adaptation data in the form of a transmission control unit log (do not reset the adaptation values).

3. Re-adapt the problem shift using the adaptation process in Star Diagnosis and print a post process transmission control unit log.

NOTE: For downshifts, the vehicle must coast to a stop without braking in order for adaptation to occur.  For upshifts, the vehicle must be driven and shifted within the valid torque window (green zone in torque display in Star Diagnosis).

If the condition still exists after adaptation, compare adaptation values before and after the adaptation test drive. If the values for the filling times of these shift operations are close to the negative limit of -20 cycles (between -15 an -20), but move further into the negative with further adaptation, this may have the following cause/remedy:

CAUSE A

An incorrectly installed retaining ring for return spring B1 or B3.

REMEDY

1. Remove the transmission.

2. Disassemble multi-disc brake B1 and B3.

3. Remove/install/replace the retaining ring and disc spring.

NOTE: There are two different versions of the B1 and B3 multi-disk brake. It is essential to ensure that the retaining ring is ordered correctly. Refer to Figures 1 through 3 shown here.

Figure 1: : Notice the differences in the two versions of the B1 and B3 multi-disk brake.
<p>Figure 1: : Notice the differences in the two versions of the B1 and B3 multi-disk brake.</p>

Figure 2
<p>Figure 2</p>

Figure 3
<p>Figure 3</p>

4. When assembling, insure that the anti-twist locks are correctly positioned (see Figure 4).

Figure 4: Verify correct positioning for the anti-twist locks for the thrust bearing.
<p>Figure 4: Verify correct positioning for the anti-twist locks for the thrust bearing.</p>

5. Completely reset all adaptation data.

6. If shift quality complaints still occur, the affected shifts must be adapted before further steps are taken.

CAUSE B

Warped discs of the B1. This can be determined by placing them on a flat surface and inspecting.

REMEDY

1. 1Replace discs of B1, disc spring and retaining ring.

2. Completely reset all adaptation data.

PARTS

QTY       PART                                                             P/N

2………..Circlip (snap ring) for variant A and C………A220 994 03 40

2………..Circlip (snap ring) for variant B and D………A001 994 18 40

2………..Disc spring……………………………………A220 993 02 26

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