Is your 1999 Mercedes E320 windshield wiper motor giving you trouble? Don’t let a faulty wiper motor compromise your visibility during rain or snow. Replacing it yourself can save you money and give you the satisfaction of a job well done. This comprehensive guide will walk you through each step of the windshield wiper motor replacement process, ensuring a smooth and successful repair for your Mercedes E320.
Inspection and Preparation: Diagnosing the Issue and Getting Ready
Before diving into the replacement, it’s crucial to understand the problem and prepare your workspace.
Step One: Inspecting the Wiper Transmission for Issues
Once you’ve removed the wiper motor, take the opportunity to thoroughly examine the wiper transmission. This mechanism is responsible for converting the motor’s rotational motion into the sweeping movement of your windshield wipers. By manually moving the transmission linkage, you can assess its operation, noting the movement range, contact points, and any stiffness or binding.
In my case, the transmission felt surprisingly stiff, though it’s hard to say if this was abnormal without a point of comparison. This step is also a great chance to disassemble your old wiper motor. Understanding how it works can be insightful. In the images below, you can see the internal components of my disassembled motor. Notice the damaged worm gear, which unfortunately led to the destruction of the plastic gear.
It’s interesting to note that Mercedes-Benz engineers designed the system to use the plastic gear’s position, not the internal motor position, to detect the parked position of the wipers. Because the plastic gear is directly linked to the wiper position, damage here won’t cause your wipers to park in an unusual location. Instead, the motor might continue running even when the wipers are stuck, humming away until it times out due to not detecting the park position. In some cases, like mine, you might be able to manually nudge the wipers back to the park position when they get stuck.
Step Two: Cleaning the Wiper Transmission Linkages
With the transmission exposed, take the time to clean it thoroughly. Use a brake parts cleaner to remove the old, likely grit-filled grease from the linkages. Pay close attention to all contacting points and surfaces. This isn’t just a superficial cleaning; it’s about addressing potential underlying issues. A buildup of old grease and debris can contribute to stiffness and premature wear in the wiper system. A good cleaning provides peace of mind and ensures smooth operation of your newly installed wiper motor.
Step Three: Lubricating the Wiper Transmission
Proper lubrication is essential for the longevity and smooth operation of your wiper system. You might not be able to see all the internal moving parts of the transmission, but there’s a crucial gear mechanism inside. A small gear interacts with a reverse gear as the wiper moves back and forth, creating the characteristic “M” motion.
To lubricate this internal gear, locate the three holes that align when the main post is in the vertical position. Using the straw attachment on your white lithium grease spray, carefully apply lubricant into these holes, aiming the straw to reach different areas within. Don’t forget to lubricate all other visible moving parts of the transmission linkage as well. Manually move the linkages to distribute the grease and repeat the lubrication process as needed to ensure all components are well-lubricated.
Step Four: Parking the New Wiper Motor (Before Installation)
This step is crucial and should be done before attaching the new motor to the transmission. Ensure your car is turned off. Replace the wiper motor fuse and plug in the new motor, keeping it unattached to the transmission. You might need a helper to hold it securely.
Get inside your Mercedes E320, turn the ignition to the “on” position (without starting the engine), and test the wiper motor functions. First, test the intermittent wiper setting, observing if the motor runs and stops correctly. Then, test the slow and high-speed settings, noting the motor’s sound for comparison later. Activate the windshield washer sprayers to ensure the motor briefly activates and shuts off as expected. Finally, run the wipers on the slow setting for a short period, then turn them off and allow the motor to come to a natural stop. Turn off the ignition, remove the key, unplug the motor, and remove the fuse. This process parks the new motor in the correct starting position, making it ready for installation.
Installation: Putting It All Back Together
With the preparation complete and the new motor parked, you’re ready for the installation phase.
Step One: Attaching the New Wiper Motor to the Wiper Transmission
Position the new wiper motor onto the wiper transmission and secure it using the three bolts. While the motor is parked in the starting position, you now need to align the wiper transmission into its parked position before attaching the main arm of the transmission to the motor shaft.
Because the wiper motor rotates continuously in one direction, and the transmission dictates the back-and-forth wiper motion, you have some flexibility in the initial wiper position. You could technically set it to start on the passenger side, in the center, or at any angle you prefer. However, for factory settings, there’s usually an alignment mark on the transmission linkage to guide you. This mark (or just visual common sense) will indicate the correct position before reattaching it to the motor. Don’t stress about perfect alignment; slight deviations are usually acceptable.
In my case, the arm wasn’t perfectly aligned with the mark, but it worked fine. Press the transmission arm onto the motor shaft and tighten the nut. As you tighten, you might encounter the motor’s internal friction and it might start to turn. This is where a 13mm open-end wrench becomes useful, as a socket wrench might be obstructed by the linkage. If the motor rotates during tightening, use the wrench to gently turn it in the same direction until the transmission arm aligns with the parked position mark again. Avoid turning it backward, as this could loosen the nut or even damage the new motor, potentially leading to another replacement sooner than you’d like! Ideally, re-park the motor before plugging it back in to prevent unexpected movement when you turn the car on.
Step Two: Installing the Wiper Motor and Transmission Assembly as a Unit
Carefully “roll” the assembled wiper motor and transmission into the damper bushing, securing it with the bolt. Then, let the other damper bushing (attached to the assembly) rest in the white clip, and align the bolt holes with the corresponding bolts on either side. Ensure the flange is properly seated in the damper bushing before tightening the bolt – only about a quarter turn is needed. Do not overtighten. This bolt is designed to turn on a plastic ramp and primarily functions to absorb vibrations, not to provide a strong clamping force.
Next, clamp the white clip over the other damper bushing. Pliers, set to a wide setting and clamping on the very top of the clip, might be necessary to fully close it. It can be difficult to close the clip completely by hand; it should click securely into place and require a decent effort to remove by hand once properly installed. The challenge is compressing the bushing, which can be quite stiff. Once the clip is secure, reinstall the two nuts and proceed to the next step.
Step Three: Plugging in the Motor and Installing the Motor Fuse
Your new wiper motor should come with a rubber grommet along the wire. Your Mercedes E320 will also have a similar split-grommet on the vehicle itself. Route the motor wire through the vehicle’s grommet and then install the grommet from the new motor into the sidewall of the fuse panel. Note the grommet’s shape; it’s designed to fit in only one orientation. Pull most of the wire back out of the fuse box through the grommet to provide slack and make it easier to close the fuse box cover later. Connect the motor power cord to the motor, and then reinstall the wiper motor fuse. You’re now ready for testing!
Step Four: Testing Motor Operation
Get back into your Mercedes E320 and test the wiper motor operation. With everything bolted in place, there’s little that can go wrong mechanically. Mercedes-Benz engineers have designed the system to prevent the wipers from extending too far in either direction or to the sides.
This test allows you to confirm that the wipers stop in the correct parked position. Pay close attention to the sound of the new motor and compare it to the sound you noted during the initial parking test. This is your last chance to detect any unusual strain on the motor, which could indicate a persistent issue with the transmission linkage despite cleaning and lubrication. If you haven’t already, and if you are testing without a wet windshield, do not install the wiper arms yet. Running wipers on a dry windshield can put excessive strain on the motor. You can also use this testing opportunity to apply additional lubricant to the linkages while they are in motion, if needed.
Step Five: Installing Primary and Secondary Fuse Box Covers
If the wiper motor test is successful, turn off the wipers and the car, and for safety, remove fuse 44 again. Reinstall the secondary fuse box cover and screw it in place. Then, replace the primary fuse box cover.
Step Six: Installing the Fresh Air Ventilation Duct
This is the larger ventilation duct piece. Remember that the shroud located under the wiper transmission needs to be installed first, as two or three screws for the ventilation duct mount through it. Slide the shroud into its position, and then maneuver the ventilation duct into place. Install the plastic nuts at either end of the duct – remember not to overtighten them, as they are plastic. Then, install the ten screws that secure the duct. You might need to slightly adjust the alignment for each screw to get them started, so don’t fully tighten any screw until you have started all of them. Once all nuts and screws are in place, secure all the clips to finalize the installation.
Step Seven: Installing Driver and Passenger Ventilation Intake Registers
When you removed these ventilation intake registers, you likely focused on the three clips. Now, flip them over and you’ll see additional clips on the back that slide underneath the plastic cowl near the windshield. Align everything carefully and slide all the clips in simultaneously to properly reinstall these registers.
Step Eight: Attaching the Wiper Transmission Cover
The wiper transmission cover simply clips into place, with the rod passing through the designated hole at the end of the cover. This is a straightforward step.
Step Nine: Attaching the Wiper Arms
Remove the 5mm hex head bolt from each wiper arm post. Slide the wiper arm over the post and reinstall the bolt, tightening it securely. Remember that the wiper arms are spring-loaded, so you might need to apply a little pressure to properly position them before tightening the bolt. Finally, attach the wiper blades to the arms.
Step Ten: Wetting Your Windshield and Final Testing
Almost done! Don’t forget to reinstall fuse 44! Now, wet your windshield thoroughly with water or washer fluid and perform a final wiper test to ensure everything is working perfectly.
Congratulations! You have successfully replaced your 1999 Mercedes E320 windshield wiper motor. Clean up your workspace, put away your tools, and take your Mercedes for a test drive, enjoying the clear visibility provided by your newly functioning wipers.
Maintenance Tips
To keep your wiper system in optimal condition, you can periodically perform some simple maintenance. By removing just the wiper blades, wiper arms, and the plastic cover, you can easily access the wiper transmission linkage for relubrication. If you run your wipers and stop them mid-cycle, you can even access and lubricate some of the internal gears. For more thorough lubrication of the rear linkages, you might consider removing the ventilation intake registers again. Regular lubrication will help ensure smooth, quiet, and reliable wiper operation for years to come.
If you encounter any issues during this replacement process, please feel free to ask questions in the comments below. Sharing knowledge is what these communities are all about! This guide aims to be comprehensive, addressing the shortcomings of previous guides and providing all the details needed for a successful DIY windshield wiper motor replacement on your 1999 Mercedes E320. Enjoy the improved visibility!
