Article by: Paperplane94
Applies to: all e32 and e34 models
I recently replaced the door lock actuators in my car, but instead of replacing the entire actuator I just bought some small DC motors of the same size to replace the old ones.
(This only works for the early actuators and not the box shaped ones).
If you are very impatient and hate tedious work then read no further and just buy the whole actuator.
Buy the motors (5 for doors and fuel filler door, not including trunk. You may have to buy one more). I got mine here:
If the link doesn’t work then the sellers name was OEM Parts Inc., and you need the Mabuchi FC-280SA 12v motors.
Here goes . . . please try to read everything, can’t miss details.
Begin by removing the actuator from the door, good write up here except you don’t have to cut the arm off the actuator unless its stuck in the double lock mode and you don’t have to remove the entire lock assembly, just the actuator.
I just used a small crescent wrench to remove the actuator mounting screws.
With the actuator on a work table pry open the top cover on the actuator housing. Be gentle and pry outwards, there is a PCB in there and you don’t want to damage it.
Here it is apart (drivers lock actuator): A few parts: notice the micro switch that contacts the actuator arm.
This allows you to unlock/lock the door by pulling/pushing on the door lock button.
Only the drivers and front passenger actuator has this switch.
There is a plastic gear with a gear that connects to the actuator arm.
Also in the top of the pic below, there is the double lock deadbolt (kinda blurry). It fits into that hole in the PCB.
Next, take out the PCB by pressing it out from the bottom where the connector goes(use your finger).
There is a rubber gasket where the connector goes, don’t lose this, it keeps the water out.
There are two motors in every actuator (except the fuel door and trunk), one large motor for normal locking/unlocking, and one smaller motor for the double lock deadbolt.
We will be replacing the normal lock/unlock motor only (large one with a gear on it).
If you carefully move the PCB and associated wires out of the way you will see a small plastic tab sticking out.
First remove the actuator mounting screws as they hold in this plastic piece.
Use needle-nose pliers to remove the plastic piece straight up.
Pliers on plastic piece (Remove actuator mounting screws first):
Pull straight up and out:
Once the plastic piece is out the motors can be removed. Careful not to damage motors or wiring upon removal.
All parts shown here(from left to right): double lock deadbolt, plastic gear with gear inside of it, plastic piece that holds in motors in, actuator arm, and Printed Circuit Board (bottom of pic).
Motors shown removed. Smaller double lock motor on the left and large normal lock motor on the right.
(The normal lock motor pictured here is actually the new one, just for an example. That’s why it’s not soldered on. The old one was rusted through.)
My double lock motor was still working because I didn’t use the double lock feature often.
De-solder the wires and remove them from the normal lock motor.
Here is one of the new motors:
And here is the old one (molested for 20 years):
Now pictured is an old motor with the gear still on the spindle.
To remove it I just put the motor in a vice and used a large pair of wire cutters behind the gear and tapped the gear off the spindle with a hammer.
I guess you could use a gear puller but this crude way worked for me, plus they are just pressed on and not terribly hard to remove.
Place wire cutters behind gear, don’t cut off the spindle, just hold it there.
Hit it with a hammer, you don’t have to use a mallet like the one shown, just a regular hammer.
Be careful not to damage the gear, you can damage the motor all you want as you will not be re-using it.
The hard part was figuring out how to put the gear on the new motor. I thought about using loctite or something similar but instead just crimped the spindle, just like the old one.
All I did was used a pair of vice grips to clamp the new motors spindle.
You do not want to clamp down too hard or you will distort the spindle, just bite down enough so that the gear can be pressed/tapped back on the motor with resistance.
Tap the gears on with a mallet (hammer if your careful), its a good idea to find a hole that is the same size as the spindle and tap the gears on so the spindle has room to emerge out the other side of the gear.
Be sure to tap the rear of the motor where the spindle emerges out of the plastic.
New motors with gears on them (and without):
After that solder the new motor to the corresponding wires on the PCB.
The polarity does matter, so once you have re-assembled everything test to see if the polarity is correct and that the motor is unlocking/locking when it should.
Assembly is pretty straight forward.
Scrunch the motors in, plastic piece back to where it belongs, plastic gear and double lock deadbolt back in, pcb back into the connector holes, rubber gasket where connector is(mentioned above).
Everything back where it should be, except the actuator arm:
Once you place the cover back on, test the motors polarity by plugging them back to the cars connections and seeing if the actuator arm moves out when unlocking and in when locking (depending on door or fuel flap or trunk).
If the double lock is working(you wont be able to pull out the actuator arm if its working). If its not the correct polarity simply switch and re-solder the motors wires.
Cover back on, don’t adhere it back yet in case the polarity needs to be corrected:
Once the actuator polarity checks out ok, mark the actuator somehow so you know its working correctly.
Use super glue or similar adhesive to adhere and seal the cover back on. Don’t use too much, the arm must still move freely.
All re-assembled, glued together. A little silicone sealant around the cover may also keep out rain and moisture. Don’t forget the rubber boot.
As you can see, you will need a few skills to tackle this job:
- General knowledge of DC circuit
- Know how to solder
- know how to crack open the door panel (not literally)
- have the guts and patience to do/read this, and maybe small hands too.
BTW in case you were wondering, the motors have brushes that wear out over time. I dissected a few of the old motors and found this:
On the left are brushes that are shot, on the right are partially intact brushes that still work.