Mono Windshield Wiper Gear Failure

Preventative maintenance is the key to long life

This applies to all 201, 124 and 129 chassis with the single windshield wiper armThis is an alert that should be heeded if you own one of the above cars. If the wiper hub assembly is not properly lubricated the internal fiber gear teeth may wear out leaving your wiper mechanism unusable. This is not a good thing to happen on a dark rainy night. You can not find any information in the factory manuals on servicing this assembly nor can you buy a replacement gear! If the gear fails you have to find the entire wiper assembly. 

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Problem & Solution

Common among these chassis:


This gear is located inside the wiper hub assembly at the base of your windshield. Its purpose is to move the wiper arm in and out as it sweeps across the glass. The only way to access this gear is the remove the entire wiper assembly from the firewall and disassemble it from the back side. I know this is not easy but better than having the unit fail when you least expect it! 

From my experience there seems to be two reasons why this gear fails:

  1. The original grease applied to the gear at the factory becomes dry and hard and no longer provides adequate lubrication.
  2. The mechanism that drives the round steel shaft that is coming out of the arm of the hub (wiper arm bolts to this shaft) binds up and puts stress on gear teeth. This binding is due to lack of lubrication over many years of use.

The prevention is lubrication. If you are not motivated to take the assembly apart right away to repack it with grease, then you should (at least) immediately lubricate the steel shaft (as pictured). This can be done without any disassembly. Just a few drops on the sleeve bushing every couple months should do the job. Automatic transmission fluid makes an excellent lubricant here. If you drive in heavy rain you might want to lubricate the shaft more often.

The best recommendation however, is to remove the entire unit from the car, take it completely apart, and thoroughly lubricate it with synthetic grease. See Kent's mono wiper video for more detail.

Note on gear replacement: If your plastic gear fails or is worn out, I recommend purchasing a used wiper assembly from a recycler. Pull it apart for inspection and repacking. Use the good gear in your old assembly or install the complete unit. Don't even think about buying one of these new. If you have the chance to pick up a wiper assembly cheap then do it. The value of these is only going to go up in the future. A spare gear on hand can be set aside for a rainy day...