Is your 1996 Mercedes-Benz driver’s side window struggling to go up or down? A common culprit is a failing window motor and the associated bracket and gear mechanism. This step-by-step guide will walk you through replacing the motor and indexing the sector gear, ensuring your window operates smoothly once again. While this guide focuses on a 1996 Mercedes-Benz, the principles can be applied to similar models.
Motor Replacement and Sector Gear Indexing for Your Mercedes-Benz
This process details how to remove the old window motor, replace it with a new one, and crucially, correctly index the sector gear. Proper indexing is vital for the window regulator to function correctly after the motor replacement.
- Secure the Motor Bracket:
Begin by firmly securing the motor bracket in a vise. As shown in Picture #8, position the bracket at an angle, approximately 15-30 degrees upwards. This angle prevents the sector gear from hitting the vise when it’s fully engaged, which is important for accessing rivets and bolts later in the process. Maintaining the gear’s full range of motion is key.
- Tighten the Vise Securely:
Ensure the bracket is absolutely secure in the vise. Use a heavy-duty hammer (BFH – Big F*ing Hammer) to give the vise handle 2-3 good, solid blows to tighten it further. Refer to Picture #9** for visual guidance. A stable setup is crucial for the next steps involving rivet removal.
- Rivet Removal:
Removing the old motor requires dealing with three rivets. You’ll notice that at least one of these rivets is hidden behind the sector gear. Therefore, you need to remove the rivet heads from the front side. As illustrated in Picture #10, target the rivet heads in positions 1, 2, and 3. When you’re almost through the final rivet head, make sure to maintain a firm grip on the motor to prevent it from dropping once the rivets are removed.
- Motor Removal and Lever Arm Management:
Now, refer to Picture #11. With one hand, gently lift the lever arm just enough to allow you to remove the motor with your other hand. Once the motor is out, carefully release the lever arm, letting it rest against the vise. Continue to remove the rivets from positions 1 and 3. For the position 2 rivet, you’ll need to lift the lever arm again until the sector gear provides enough clearance for removal. After removing the final rivet, release the lever arm back to its resting position. Your regulator assembly should now resemble Picture #12.
The vise is crucial here as it safely absorbs the spring recoil of the window regulator mechanism. As you can see in Picture #12, with the motor removed, the spring tension on the lever arm is now safely contained by the vise, preventing any sudden or uncontrolled movements.
- Preparing Button Head Screws (Optional Grinding):
For the next step, a grinder might be needed. If you intend to use new rivets instead of standard fasteners, you can skip the grinding. However, General Motors (GM), like Mercedes-Benz, often used rivets for cost-effectiveness and clearance. Standard nuts and bolts are often too tall and can interfere with the sector gear’s rotation. Button head screws are a good alternative, as they are low profile and can be tightened with an Allen wrench.
To ensure clearance, grind down the tops of two of the three button head screws. Aim to remove approximately 1/3 to ½ of the screw head’s height. This modification shouldn’t compromise the screw’s integrity for this application, while still allowing sufficient space for an Allen wrench to tighten them.
- Test Screw Clearance and Install:
Grind the tops of two of the three button head screws until you achieve at least 1/16th of an inch clearance between the screw’s highest point and the sector gear. You can test this by inserting the screws into position 3 (refer to Picture #10) on the motor bracket. Lift the lever arm (as shown in Picture #11) until the sector gear is behind the screw head to check the clearance. The third screw at position 1 does not require modification as it doesn’t interact with the sector gear. Once modified, the screws should look similar to Picture #13. Insert all three screws into the backside of the motor bracket, ensuring the heads face the sector gear and the threads are ready to receive the new motor.
- Sector Gear Indexing Mark:
Locate the indexing mark on the back of the sector gear, as highlighted in Picture #14. This mark is crucial for correct motor installation.
- Align Indexing Mark and Install New Motor:
Pull up the lever arm until the indexing mark on the sector gear aligns precisely with the motor bracket, as shown in Picture #15. Install the new motor, carefully maintaining the exact orientation of the indexing mark and the motor bracket as depicted in Picture #15. Correct alignment at this stage is critical for proper window operation.
- Secure Motor with Nyloc Nuts:
Using Nyloc nuts, follow this tightening sequence:
a. Snug, but do not fully tighten the position 1 screw.
b. Thread and fully tighten the position 3 screw.
c. Thread and leave loose the position 2 screw.
d. Fully tighten the position 1 screw.
Once completed, the assembly should resemble Picture #16.
- Final Screw Tightening Using 12V Power Supply:
To tighten the final screw at position 2, you’ll need to manipulate the sector gear electrically using a 12V power supply. The replacement motor used here was a Dorman 742-103. This motor often comes with two pigtails, one of which should fit your Mercedes-Benz door connector. Use the incompatible pigtail for this step. Attach this pigtail to the new motor, remove the plastic housing at the other end to expose the terminals. Briefly connect these terminals to a 12V battery. This will move the sector gear. If it moves in the wrong direction, reverse the polarity of the pigtail connections to the battery. Move the sector gear downwards until you can access the back of the position 2 screw. Refer to Picture #17. Tighten the screw as shown in Picture #18.
- Pre-Installation Gear Positioning:
Finally, use the 12V power supply to “bump” the motor until the gear is positioned approximately halfway on the sector gear teeth, as shown in Picture #19. This halfway position will facilitate easier installation of the entire assembly back into the door of your 1996 Mercedes-Benz.
- Motor Pin Length Issue (Note):
Be aware that some replacement motors, like the Dorman motor mentioned, may have a main pin that is too long. Picture #20 illustrates this potential issue. You may need to address this pin length before final installation.
Stay tuned for further instructions on resolving the motor pin length issue and completing the installation.
