Auxiliary fan failure analysis and used part request

[Duke2.6]

This was an interesting failure that I don't think has previously reported.

On my 1988 190E 2.6 one of the two aux. fans would only turn in the opposite direction of normal rotation with some difficulty and made a "ratcheting sound".

The field consists of three permanent magnet segments that are held on the motor frame with spring clips at the ends of the segments. One spring clip was bent up, which interfered with the armature segments, effectively jamming the fan.

DC motors draw maximum currrent at stall, so with insufficient torque to move the fan, the brushes and brush blocks got fried.

If anyone has a used, serviceable motor, I'd be interested. The back of the frame is ink stamped "750" with "118" below. A parts seach indicated that this motor is used on a lot of previous models including 123s, so it's probably fairly common.

If the armature spins smoothly and there is electrical continuity between the power and ground leads, the motor is probably okay.

An archive search on the aux. fans proved very helpful - especially the fact that the fan retention nuts are left-hand threads. After bending back the French lock tab, I was able to loosen the nuts with a 25/32" (actual size is probably 20 mm) socket on a breaker bar while holding the fan hub from turning with my hand.

Duke

[Duke2.6]

The arrow points to the bent field magnet spring clip.

Note the melted brush and brush holder material compared to the good motor.

Duke

[Duke2.6]

...finally got around to getting the auxillary fans squared away... bought a used motor from a later model 190E 2.6 at a local pick-a-part boneyard for twenty bucks, and it tested okay on a battery they had, so I knew it worked, but someone had cut the connector off the pig tail.

The boneyard fan had well worn brushes compared to my originals, and the front ball bearing was very dirty and rough, so my plan was to use the boneyard main housing with my original armature and frontplate/bearing. The boneyard motor did not have the yellow device that can be seen in the photo in post #2. I identified it as a capacitor that spans the 12V and ground inputs, and some EE friends felt it is there purely for RFI purposes.

Once I got the boneyard ball bearing cleaned up it spun freely with maybe just a hair more roughness than the originals from my car, but when I tried to fit the original front frame/bearing to the boneyard housing it wouldn't slip into the circumferencial depression. Further investigation revealed that that my original front frame and main housing are about .050" larger in diameter than the boneyard front frame and housing, and after trying to file down the OD, but not making much progress I said f-it, greased the bearing from the boneyard motor front frame and put it together. So the configuration is the boneyard main housing and front frame/bearing with the armature from my OE motor. I'm left to ponder why DB made those dimensional changes.

After trying to determine polarity as best I could - it's not at all obvious - I soldered my original pigtail to the used frame, and when I was ready to fit the whole assembly to the car I connected both motors to the vehicle harness connectors and the boneyard motor ran backwards! Rather than messing with the solder joints again, I just swapped the pins in the pigtail connector, but no one will ever know except us.

BTW, when installing the fan assembly I could not get a straight shot to get the driver's side lower radial screw stated, so I ended up removing the bumper, which I should have done in the first place. There are only four 13 mm nuts that hold the bumper studs to the frame horns plus 10 mm hex screws that hold the bumper surrounds to brackets in the front wheel housings. The whole bumper/valence assembly is very light and with only six fasteners, it's easy to R & I. There's enough slack you can pull on the outside temperture probe harness to lay the bumper face down on a couple of Sam Adams cardboard 12-packs to keep from marring the bumper face.

Duke

[Ducks fan]

Duke2.6: How do you remove the fan? We removed the body-colored center brace and expected the fan to lift out after unbolting, but could not do so. It's like changing the headlight bulbs--once you understand the trick to the mechanism, it's easy. Until then, it seems impossible. Also, do both fans have to be removed at the same time or are they completely separate units in terms of their mounting?

Thanks again for everyone's input. Will let you know if any of the suggestions help identify the problem.

[Duke2.6]

You remove the entire fan frame, then remove the fans from the frame. There are four small radially oriented bolts that hold the fan frame to the radiator support - two about 45 degree above the horizontal and two 45 degrees below.

It's best to remove the front bumper assembly first. It's easy. There are four nuts that hold the bumper to the frame horns, and two small bolts that hold the bumper surrounds to a bracket that you access from the wheel wells.

The bumper assembly is actually quite light because the structural member under the cover is aluminum. You should be able to get enough slack in the temp sender wire to lay the bumper down on a couple of boxes right in front of the car.

Duke

[daphatch]

Originally Posted by Duke2.6

You remove the entire fan frame, then remove the fans from the frame. There are four small radially oriented bolts that hold the fan frame to the radiator support - two about 45 degree above the horizontal and two 45 degrees below.



It's best to remove the front bumper assembly first. It's easy. There are four nuts that hold the bumper to the frame horns, and two small bolts that hold the bumper surrounds to a bracket that you access from the wheel wells.



The bumper assembly is actually quite light because the structural member under the cover is aluminum. You should be able to get enough slack in the temp sender wire to lay the bumper down on a couple of boxes right in front of the car.



Duke

Great thanks for the input