notsofast
Active Member
- Joined
- May 4, 2015
- Messages
- 251
- Car
- CLS320Cdi
My CLS failed is MOT for "light intensity significantly reduced in the mirror unit LED" amongst a few other items. Whilst waiting for some of the suspension components that I have ordered to arrive, I took some time to sort out the passenger door mirror. The power folding worked when I bought the car a few years ago but became intermittent before ceasing to work at all so figured I would strip it all down and work out what the issue was. Based on what I had read on the forum I suspected the wiring at the articulating area might be causing both the dim indicator and also the folding motor issue.
Quite difficult to spot all the screws and clips but I got the unit apart without any damage but decided it would be easier to work on it if I removed it from the door. The voltage at the led indicator unit connector was good so I removed the indicator unit from the opposite door and connected it to the connector and it worked perfectly so seems like I have a dying indicator unit. It is a sealed unit so I ordered a new genuine MB item (P/N A2198200521) as it was barely more expensive than the pattern items available. I may cut the old one open later to see if there is anything repairable but there are no signs of water ingress, connector corrosion or other damage.
The folding mechanism is powered by a tiny DC motor with hard end stops on the pivot. It runs through a small worm drive gearbox and operates in both directions simply by reversing the polarity. The power is applied for a few seconds and the motor stalls at the hard stop. It may be a voltage sensing circuit measures the drop at end of travel and cuts the power but I suspect it is simply a timer. Regardless, the wiring was fine but the motor itself was faulty. It is similar to the small motors in kids toys so I pulled the end cap off and there was a lot of black carbon dust around the commutator end. The brushes looked fine so I cleaned it all up and put it back together. A pair of very tiny thrust washers were a little tricky to position behind the brushes however it tested fine using a PP3 9v battery.
I refitted the mirror chassis back on the door and will fit the new indicator when it arrives but the folding mechanism works for the first time in a couple of years now.....
Quite difficult to spot all the screws and clips but I got the unit apart without any damage but decided it would be easier to work on it if I removed it from the door. The voltage at the led indicator unit connector was good so I removed the indicator unit from the opposite door and connected it to the connector and it worked perfectly so seems like I have a dying indicator unit. It is a sealed unit so I ordered a new genuine MB item (P/N A2198200521) as it was barely more expensive than the pattern items available. I may cut the old one open later to see if there is anything repairable but there are no signs of water ingress, connector corrosion or other damage.
The folding mechanism is powered by a tiny DC motor with hard end stops on the pivot. It runs through a small worm drive gearbox and operates in both directions simply by reversing the polarity. The power is applied for a few seconds and the motor stalls at the hard stop. It may be a voltage sensing circuit measures the drop at end of travel and cuts the power but I suspect it is simply a timer. Regardless, the wiring was fine but the motor itself was faulty. It is similar to the small motors in kids toys so I pulled the end cap off and there was a lot of black carbon dust around the commutator end. The brushes looked fine so I cleaned it all up and put it back together. A pair of very tiny thrust washers were a little tricky to position behind the brushes however it tested fine using a PP3 9v battery.
I refitted the mirror chassis back on the door and will fit the new indicator when it arrives but the folding mechanism works for the first time in a couple of years now.....
