126 chasis '87 300sdl heater/blower r&r

[Bart]

Need to R&R heater/ac blower motor. Motor just started squealing upon startup or when it runs on low. I suspect it is a bad bearing. What are the steps to R&R the motor. I also suspect this is non serviceable and will have to replace the whole motor.

[Robby Ackerman]

Sounds like you need to get the CD (shop manual).

I don't know about the SDL, but on my '87 190 I remove the cowling below the windshield and the motor is right there. Using a long screw driver I can drip some transmission fluid on the bearings and quiet them for a year or so.

If you buy a new motor get it with the fan blades already attached. You'll likely be unsuccesful in transferring the old brittle blades without breaking them. Smitty's has Bosch motors at a decent price ... www.sasponline.com .

[Bart]

Thanks for the info. I understand that transmission fluid is the only lube to use on blower motor.

[Robby Ackerman]

You are welcome.

[GeorgeMurphy]

Need to R&R heater/ac blower motor. Motor just started squealing upon startup or when it runs on low. I suspect it is a bad bearing. What are the steps to R&R the motor. I also suspect this is non serviceable and will have to replace the whole motor.

If over 140,000 miles or so, it may need brushes - I have them - here's how to change:

Blower Motor Brush Replacement

123/126 models (Draft)

Remove the underdash panel on the passenger side. (126 models - open the clips on the heater plenum and drop it down). Unplug the electrical plug - the blower is held with three 8mm hex head screws - remove them and drop the blower assembly from the heater plenum.

Open the cover on the electrical connector and disconnect the two wires.

Remove the screw(s) holding the blower motor to the frame and slide it from the frame by pushing through the hole in the frame.

Blow out all the dust from the motor - be careful not to dislodge the little "hairpins" on the cage vanes - they are balancing weights for the cage. Do this outdoors to avoid breathing dust.

Do not remove the armature - simply open the tabs on the end of the brush holders (watch for the spring), cut the old shunt wire next to the brush, and remove the spring and brush.

Before working with the new brushes, lightly solder the very tip of the shunt wires so they do not unravel and look like a horse's tail . . .

Install the new brush - watch the correct taper direction - and the spring. Bend the tabs back over to restrain the spring as original.

You may connect the old shunt wire to the new one like I do - I cut off the tubular portion of a #10 wire terminal and use it as a splice - feed the old shunt in from one end and the new one in from the other. Adjust the lengths so the shunt wire does not touch the motor frame (short circuit), and then slightly crimp the terminal. Solder the joint for good electrical connection. One shunt wire may be soldered directly to a lug inside the motor frame on some 123 motors.

Slight grooves in the commutator will not hurt anything and new brushes will soon conform to the groove . . .

Lubricate the bushing with auto transmission fluid - (will not dissolve winding insulation) DO NOT USE WD-40 OR ENGINE OIL

Blower motor squirrel cage installation


Removal and re-installation of the blower cage requires care – do not place excessive force on the cage as it is easily damaged and replacements are not available from MB!

Be careful not to lose the little “hair pins” in the blades – those are for balancing the cage

Refer to the diagram to the left – rest the cage to suspend the motor between two pieces of 2 x 4 wood about 6” long. Use a suitable punch to carefully drive the old motor out of the cage.


Start the cage on to the new motor shaft, and then rest the opposite end of the motor shaft on a suitable rest held in a vice so that the force used to drive the cage on to the shaft is transmitted through the shaft to the rest. If you don’t do it this way, you risk irreparably damaging your new motor . . .