how to: E36 rear door lock actuator removal

[DougInAmbler]

The lock button on the left rear door of my '97 328i was intermittently getting stuck in the up or down position. So at some times I couldn't lock it and other times couldn't unlock it. It settled out in the unlocked state, so at least I could use the door, but I couldn't really secure the car anymore.


Temporary solution: I removed the Lock Actuator (aka lock motor module), found it defective, and left it removed. Now I can lock/unlock via the manual button, which is OK for now.


Full solution: I will probably install a new Lock Actuator module (Part #51 22 8 122 419, about $119 from Bavarian Autosport or $190 from dealer).


It took me a while to figure out how to remove the Lock Actuator from the door. My Haynes manual incorrectly said it could only be done by removing the window glass, which I wanted to avoid. But you don't need to remove the window and the job is not too hard once you figure it out.


First, the following "how-to" thread was very helpful though long, and it only refers to the front door lock:
http://forums.bimmerforums.com/forum...ad.php?t=90469
Thanks to writer XOC for that.


Here's my method, for e36 rear door lock actuator removal:
1. Remove door panel
2. Remove 3 big screws holding latch mechanism at rear of door
-now you can move the entire latch mechanism around in its door cavity, though you can't see it well and you can't remove it because the window track is in the way. Wiggle it all the way forward so you can see where the rods hook into it.
3. Remove the operating rods:
-the lock button rod goes to bottom hole in latch
-the door handle rod goes to top hole in latch
4. Remove the 3-wire connector
-the connector is cleverly locked in place by a cam-collar. Slide this firmly down (perpendicular to the wires) until the connector pops open, then you can wiggle it straight off the pins. You can also do the job without disconnecting this, if you find it hard.
5. Remove the Lock Actuator
-This is tricky. The (plastic) actuator is only clamped to the (metal) latch mechanism with a hard-to-see latching hook on the outside face of the actuator. At first you can't see it or get to it, but look through the empty hole in the rear edge of the door (from where you loosened the whole latch mechanism), while you twist and rotate the mechanism with your hand slid through the inside wall of the door. You will eventually glimpse the outside wall of the actuator, where a plastic strap can be felt and seen. Now you can insert a knife or thin screwdrive through the latch-hole and pry the strap outwards, and the actuator will pop off loose.




Post mortem of Lock Actuator:
The module can be carefully pried apart. Inside it contains a reversible DC motor, driving a nylon lead screw through brass pinion and nylon gear. A threaded nylon carriage is driven forward or back, with a tab protruding through a slot that operates the mechanical lock lever below the module. The carriage trips a SPDT microswitch at one end of travel, so that each operation will enable reverse current for the next operation. I found two failures:
-The nylon carriage and operating tab had been 'bumped apart' mechanically, so the tab was frozen in one position. This was what was blocking the manual door lock button. These 2 nylon parts can apparently bump apart when the carriage slams into one end of travel, though there are even little steel stiffening ribs that try to prevent that.
-The Microswitch failed. The NC contact was open-circuit (2Megohms or so). So the actuator couldn't "lock". But if I put the carriage in the middle of the screw, pressed the microswitch, and "unlocked" all doors via the front door button or master button, the actuator worked fine: it turned the screw and the little carriage zipped to one end and slammed into it. IOW, the motor is fine. I believe I could repair this actuator if I could find the exact microswitch. Its 3 pins could easily be unsoldered and a new one popped in.


I note that the module has a second 'cradle' for popping in a second microswitch, which I presume is done for the 6-wire front door module, where the second microswitch detects door key rotation.

The photos show:
-Lock actuator (rear door) with cam-acting connector
-Door mechanically re-assembled, with working manual lock, leaving out the actuator shown at right
-Internals of lock actuator: white nylon operating tab sticks up at left; nylon carriage on lead screw has slider that trips red button on black microswitch at right

[Eric93se]

thanks! I actually used the search engine and found this thread, then I'm like Hmm I wonder how old it is, haha, it was like "today".

[K1118]

I did my rear actuators recently. I found that disconnecting the metal connecting rods makes the whole thing 100x easier. They just pull out of the attachment point by the door lock pin. Don't try to unscrew the damn thing.. Just pull it off and it will clip back in when you're done..

[Eric93se]

Yeah, I totally removed the rods. The only tuff part was putting the actuator back into the door.

So my switch was fine, reading about 1ohm when triggered. My problem was that the actuator would occasionally not lock or unlock. Studying the design I saw that the sides of the carriage needs to be lubricated on the sides where there is a bump on both sides. The way the mechanism works in order for the carriage to go one way then the other way, the carriage has to slide and snap over a raised part and that locks the carriage to grab when going in the opposite direction. I used a gelled lithium grease to lube this up. I also put some lube on where those two metal slats that go on the carriage and rub between the case and the carriage (not shown in your pictures).

[Eric93se]

So I did my other side and ran into some trouble but figured it out. The switch was reading 4ohms, but I worked it a bunch of times and the resistance dropped down to 1ohm. Secondly putting it back together the actuator would operate by itself but was not strong enough to operate the lock button. I found that the capacitor on the motor was bad, reading 0.8nF (nano farad), I went and put a ~228nF cap in its place, I don't know what the actual value is supposed to be but the old cap was bad. Even still the actuator would not pull the lock button up and down, I realized I didn't understand where the metal rails were supposed to go because they were just laying inside the assembly, but then figured out what DouginAmbler was saying that the metal rails insert into the carriage, so I greased them up and they slid right back into the carriage. Viola' it works again. I'm going to take apart all four and clean and grease them and make sure the rails are in place.

[K1118]

Good job!

A detailed DIY with pics or video would be greatly appreciated! I still have my driver side actuator to replace....If I can just fix the original, that would be great.

[DougInAmbler]

Since my original post I have discovered some earlier excellent references.


A detailed BMW description of the E36 locking system, with wonderful schematics:
http://www.unofficialbmw.com/images/lock.pdf


Another DIY for E36 rear door lock actuator replacement, with more pics, courtesy of contributor "Termignoni", (2007):
http://www.bimmerfest.com/forums/sho...d.php?t=131544


A tip from that thread: replacing the Lock Actuator and getting the levers to line up with the right slots in it seems to frustrate many DIY'ers. One responder says to first hook the front end of the actuator (with the wire connector) to the latch mechanism below, then gently rock and rotate it back and down until it snaps in.


Here is my summary of the E36 Door Lock Actuator (for those who can't spend a few hours with the main reference above):


Notes:
-see some photos in earlier post above
-I use the overkill term "Doorlock Button Knob" in description below just so it is very clear what that is.




The Rear Door Lock Actuator (3-pin) contains:
-A reversible DC motor, driving a nylon lead screw


-A nylon Carriage [unfortunately called 'slider' in first reference above] is threaded onto the screw, so that the Lock Computer ["ZKE" or Central Locking Module] can drive it to one of 3 (yes, 3) positions. The positions are known as Unlocked, Single-Locked, and Double-Locked.


-A "motor microswitch", tripped by an arm on the Carriage, with ramps at each end of arm. This SPDT switch helps to reverse the direction of motor and lead screw travel after each operation.


-A nylon "Slider" [my term], which floats in a groove on the back of the nylon Carriage. The Slider sticks out of the bottom of the Actuator, and has a rectangular socket to receive one nub of the mechanical "Locking Lever" that sticks up out of the mechanical Latch Mechanism below. The Slider is also mechanically coupled (by another nub on that Locking Lever) to the rear Doorlock Button Knob. So in the unlocked state, the Button Knob can simply mechanically shift the free-floating Slider back and forth, operating the Locking Lever, which has the function of de-coupling the exterior door handles from the latch mechanism. With this system even if computer function fails you still have old-fashioned mechanical lock/unlock.
When the computer has locked the doors, the Slider is no longer free-floating, so the Doorlock Button Knobs in rear doors are jammed.


The Front Door Lock Actuator (6-pin) contains:
-All of the above from rear door
-A second microswitch, SPDT, tripped by a small arm on the Slider above. This is an input to the Lock Computer, indicating that someone is pushing up or down on one of the front Doorlock Button Knobs, in which case the computer will take over and apply the operation to all doors.


Note that in the front doors, the outside key and inside door handle are also mechanically coupled to the Doorlock Button Knob, in a spring-loaded way, so they too operate the nylon Slider in the Actuator Module.


"Double-Lock" mode: This occurs when the door is locked by key (i.e. externally). In this state NOTHING will open the door except the key (or a special signal from the anti-theft device). Even if someone is locked inside!! It works as follows:
-the computer detects by separate external microswitch that the key is being used to lock.
-it drives the Carriage to the extreme position (3rd position), causing it to operate a second metal lever that sticks up from the Latching Mechanism into a side slot in the Actuator Module. This "Double-Lock Lever" mechanically de-couples the Doorlock Button Knob from the mechanical latch (trapping any occupants!).
-unlocking from Double-Lock: the computer has (hopefully) remembered that we locked with key and are therefore in "Double-Lock State". When it detects the unlock-key-turn from the key microswitch it has to drive the nylon carriage from position 3 back to position 1. This travel will make-then-break the Carriage microswitch, a very tricky operation. In theory, a 3-state switch would be ideal but in practice microswitches are 2-state.

[Carlos BMW]

Yesterday we were driving along and the driver side back door just swung open. Lock mechanism just stopped keeping the door shut. Went to the yard today and got a 'new' one. What a pain in the butt... Having to take the windows out. Oy. Got it done though.

[Eric93se]

So just to update, my actuators starting acting up again, I found that the metal slats were falling out of the carriage again. I decided on a more permanent fix, I cleaned all the old grease out with solvent, dried it with a rag, then used a dab of RTV silicone on the ends of the slats to hold them permanently in place. I'm doing all four to be done with it.

[RightYouAreKen]

This was a super helpful thread. Just replaced my left rear door lock actuator today and the steps laid out were most helpful. My old actuator was slow and intermittent...getting more so as the weather is getting colder. I decided to replace rather than repair, as the new part was only $67.50 from Pelican.

I found that removing the interior door handle and lock button pivot rather than removing the actuator rods from the latch mechanism was easier for me. As you pointed out, this thread was also helpful. http://www.bimmerfest.com/forums/sho...d.php?t=131544

Overall the job was easier than I expected. I found it was fairly easy to align the new actuator with the control bars by using a flashlight to line them up. The new actuator (Continental VDO from Pelican) makes the door lock snap up and down just as fast as the other doors now.

Thanks for the writeup!

[XTNSIV]

How long does it roughly take to replace the actuator for the first timer? I was thinking about having the shop do it since I can't remember if my '98 rear door has side airbags or not?

[RightYouAreKen]

How long does it roughly take to replace the actuator for the first timer? I was thinking about having the shop do it since I can't remember if my '98 rear door has side airbags or not?

No rear door side airbags, or even speakers for that matter. The door is pretty empty. Window regulator and door latch/lock mechanism is all.

It was pretty straightforward for me. Start to finish was probably an hour and a half taking my sweet time, which also included lubricating all of the other door latches.

[XTNSIV]

No rear door side airbags, or even speakers for that matter. The door is pretty empty. Window regulator and door latch/lock mechanism is all.

It was pretty straightforward for me. Start to finish was probably an hour and a half taking my sweet time, which also included lubricating all of the other door latches.

Perfect! I'll just do it myself then...