The following is an FYI on a repair done to correct recurring freezing of the rear wiper on our 2006 Sport Combi. Over the past few months, we had recurring incidents where the rear wiper would fail to operate. The unit would freeze in the off position, but no fuse would be blown. Initially, I was able to get it working again by backing off the retaining nut that holds the wiper arm in place, spraying penetrating oil into the bushing where the shaft passes through the glass and reseating the wiper arm. However, last week it finally failed to work after this kludge fix, so I decided to pull it apart to see what I could find.

The removal process was simplified by having an Alldata subscription that gave me the removal process. The most complicated part of the job was the removal of the fascia on the rear door to expose the motor itself. However, all bits removed easily with the part that required the most attention being the removal of the fascia cover on the inside of the rear door. It is held at the top of the door by 4 spring clips that slide over metal brackets on the door and then push onto plastic brackets on the cover. While these clips were shown in the manual, it was one of those cryptic examples where how things fit together wasn’t fully apparent until the cover had been successfully removed.

Once the cover is off, removal of the wiper motor only requires that the electrical connector be removed & 3 mounting bolts be undone - at which point the motor can be removed from the car (with the wiper arm already removed from the outside of the glass).

The motor assembly is a 2 part unit that can be opened by undoing the torx head screws that hold the gear housing together and then pulling the 2 sections apart. I found the problem was that over time water had migrated down the shaft and into the gear housing. The freezing was due to a galvanic reaction between the aluminum housing and the steel wiper shaft that had finally reached the point where the motor torque could no longer force the arm to work.

I was able to remove the shaft from the housing by mounting the housing between the jaws of a bench vise and hammering the shaft (with a nut on the threaded end to protect it) so that it pushed through the housing until it came free. After that it was a matter of removing the scale from the inside of the housing shaft and rust from the shaft and restoring the surfaces by polishing with fine sandpaper. I found that water had also travelled through the shaft into the housing itself, mixing with the factory grease and making a mess. The gear wheels are nylon and so they weren’t in danger of binding but only needed to be cleaned. I found the electrical contacts on the gear wheels were surface corroded but they only needed minor burnishing to restore them. The gears drive the motor shaft via a steel eccentric arm that was a gooey mess, but only needed to be cleaned. The shaft has a turned bearing surface about 1/3 of the way along that provides an interference fit inside the aluminum housing. The shaft was full of corroded material which is what caused the freezing. However, the bearing surface itself was still in good condition as the motor operation was sufficient to keep it polished. The freezing was caused by rust and scale building on both sides of the bearing surface until it became sufficient to keep the motor from being able to turn.

The metal shaft is covered by a rubber / plastic sleeve that is about 75 mm long and extends from the base of the housing through the window glass ending at the point where the wiper arm attaches and serves to provide a water seal. Although the seal was still visibly OK, it was clear that the orientation of the shaft on the rear window plus passage of time had allowed water to enter and lead to the corrosion I found. Based on the design, I expect this is something will happen in all cases and perhaps was more apparent in our car which lives on the West coast and is parked outside. This rubber seal looks like it was initially attached by a heat shrink process to bind it to the housing but I was able to remove it by rotating and pulling it off the base. Although the cover had no effect on the binding, it did serve to hold moisture and was a major cause of the corrosion I found. When I pulled it off, I found it was full of a water/grease/scale crud which I needed to clean out.

Once I had cleaned and polished the various parts, I re-greased everything using a water resistant grease (I used boat trailer grease), reassembled the motor assembly, mounted it and reattached the fascia parts. In total the job, start to finish, took under 2 hours, over 1 hour of which was taken up in the removal of the fascia as I worked my way slowly to ensure that nothing would break. If required to be done again (which I expect will be the case if the car is kept for a few more years), the next time I could do the entire job in about an hour.

Unfortunately, I took no pictures, but if anyone has any questions regarding the process, I’d be happy to answer. FWIW, I expect the same issue would be found on a 9-3 Sport Combi as well as they seem to have a similar, if not the same, wiper motor assembly.