Monowiper Rebuild - PeachParts Mercedes-Benz Forum

KJZ78701 · #1 04-15-2011, 08:23 PM

If you have a model with a monowiper and the wiper is stuck in the middle (you may have also smelled some electrical smoke) you probably have a broken wiper assembly gear. If you are reading this before it happens to you, please note that you will want to pull the fuse for the wiper ASAP. The wiper motor will try to return the wiper to the “rest” position. If the pieces of the broken gear prevent this motion the motor “could” burn out. I pulled the fuse as soon as the wiper stuck in the middle (I did smell smoke) and the motor works fine after the rebuild. My fuse (’92 300E) was under the hood, driver’s side near the windshield.

Pulling the assembly is not that tough, but there is a lot to remove. Start with the trim panels on either side of the wiper which will expose the screws for the water rails and the center plastic cover. You will also want to remove both weather strips that run from side to side as well as the small plastic piece that runs between the center plastic cover and the engine compartment. Note the two small screws still holding the center plastic cover down low in the front. Once all of that is out of the way you can remove the wiper (5 mm Allen under the plastic cover at the base of the wiper), and the four 6 mm nuts (10 mm head) that hold the wiper assembly in place. Remove the lower rubber/metal retaining “CLIP” and with some wiggling it will come out. If not, you can remove the nut and washer holding the metal arm on the motor and use a small gear puller to pop the arm off the motor, then remove the three bolts holding the motor to the assembly. DON’T worry about alignment at this point, I will get you all lined up when you put it back together.

Once out, use a towel to protect the finish on the cover. Turn the entire assembly over and remove the nut and then the arm sub-assembly from the wiper “transmission”. Now remove the small C clip and the washer stack below. Keep track of the order of the washers (should be thick under the C clip and then one to three thin). You can now position the wiper in the center of its travel and separate the two halves. Watch for an O ring and more washers on the shaft of the upper half as you slide it through. At this point you can remove the three screws from the upper half and carefully pry the unit apart. Wipe down the gunk on both arms and then spray it down with some WD-40, etc. to remove the rest of the gunk. You can now wipe it down again, add a couple drops of oil and clean the teeth on the gear. Turn the gear to make sure it is working well and then seal it up again. I used some RTV since the front part of the seal broke off when I pulled the halves apart. Now back to the bottom part of the assembly.

You should see a black mess in there. Remove the six screws along the semi-circular housing holding what’s left of the gear in place and clean it all. A large ultrasonic tank makes it all look brand new. J The new odometergears dot com piece did not fit perfectly so I used my grinder until it did. Nearly all of the bottom locator strip and a little bit of the front edges needed to be removed in my case to get the gear to sit all the way down into the housing. Put the two semi-circular retainers back in, apply a bit of blue Loctite to each of the six screws and tighten it up.

You can put it back together “dry” but if you must use oil or grease on the gears don’t use much. Both will just attract dirt over time. Turn the gear on the upper half until the wiper shaft is FULLY retracted. You can now slide it back into the lower assembly (a little grease on the shaft and watch for the O ring and washers again). It will only slide in to the lower half in the middle so there is no way to mess up the alignment as long as the wiper shaft is in the fully retracted position. Now put the washer stack back on, followed by the C clip.

Aligning the arm assembly is not that tough. Keeping the wiper arm in the retracted position, you will have to position the arm assembly perpendicular to the wiper shaft. I used the lower assembly as a guide (contact me for pictures). Put it back in the car, but do not attach the arm assembly to the motor just yet. Once it is all back in (careful of the lower retaining “clip”) put the fuse back in and turn the key on to just before start. You should hear the motor for a second or two. If you missed it, turn the wipers on until you are happy and then turn them back off. The motor will now stop in the “rest” position. Position the wiper (not yet installed) to point to the passenger side until the arm assembly is completely straight. It is possible to go too far, in which case you will not be able to put the arm assembly on the motor’s shaft. Position until the arm is straight and you can slide it on to the motor. Tighten the nut. If careful, you will be able to use a socket and the arm assembly to torque the nut down. As the nut gets tighter the motor shaft will turn and the arm with it until the assembly hits your socket. At this point you can torque the nut down the rest of the way. Put the wiper back on and test it out. Button it back up and you are good to go. If you want me to do it for you it will be $150 plus shipping and I do take credit cards. Note the gear is guaranteed for life. No more trips to the junkyard. You can reach me at appliedracingtech at gmail.

HTH,
Karl