SunRoof Woes: "It's Raining again..."

Having had an interesting day with the sunroof not closing properly, I thought I'd pass on my fix and save someone else some money...

The E32 sunroof is fairly simple once you look at the drive motor - both when fitted in the car and removed off the car. Two heavy coiled-wire cables push/pull the roof along tracks. If "full open" is 100% cable extension (towards the rear of the car), then "flat closed" is about 5% extended and "air vent" (rear edge raised up) is 0% extension. Of course, the system assumes:

1) the cables are "balanced" - eg same extension on both sides since both cables are driven off opposite sides of the same single drive gear
2) the motor knows best: the switches are triggered off the motor, NOT the cables or "lid" itself

My unhappiness started with a roof that opened (slid, not "tilted"), but then would not close fully. Further attempts made the 'residual opening' worse, and yet manual closing of the lid was possible and consistently so - the cables were slipping, but only for the motor? Huh? Or were the switches kaput?

OK, to fix this I tried the Bentleys' manual suggestion of re-synchronising the motor-drive to the lid - for those of you without the manual:

  1. get it
  2. the motor is under the access plate in the roof, it has the sunroof switch in it - pry down carefully from the rear edge. You can unplug blue plug from the switch - it's got little round & triangle posts on it so you can't put it on the wrong way.
  3. the procedure assumes you removed the motor drive when the lid was CLOSED, so manually close it now. This isn't strictly correct - but I'll come back to this later.
  4. Remove the motor mounting screws - three dome-head Torx screws, one on the gearbox, one below the microswitches, and another on the rearmost edge - it's the longest. They're only done up with firm hand tension. The mountings are diecast - DO NOT STRIP THE THREADS.
  5. the motor will then pull down & out - unclip the two plugs, and the white socket will come away if you move the black tang-pin in the mounting channel to the side...
Now, with the motor out, you can see the brains of the operation - the little blue cam wheel. The drive gear - that drives the wire cables - should be obvious, and not looking too worn.

The motor should theoretically be in the "closed" position - the dot/hole in the blue wheel should be in a line with a line through the drive gear shaft and the mounting hole on the gearbox outside edge - you'll see that at that "parked" position, the microswitch is just about to be closed - it's at the very end of the large notch in the cam-wheel..


Problem One: The procedure does not correct any imbalance in the extensions of the cables - it assumes the lid is already "balanced". In my case this wasn't so any more after the first episode of not shutting fully - the "air vent" position was comical, one side would rise about 3cm with the other side still fully down... however, this only showed up on this operation, not on the slide back/forwards. I'm guessing the more the extension, the more the spiral-wound wire cables were absorbing the imbalance - with only a little extension, they couldn't.

Problem Two: The procedure also doesn't account for the slack in the cam system - mine had about 2-3mm of play in the take-up of the drive gear shaft before it drove the cam, and yet the "perfectly aligned" closed position gave less than 1mm clearance to the switch activating... I guess my cables just got unlucky and on a hot day like today, got "bottomed out" by the cam causing the motor to run too long, and then the "drift" got worse from there.

SO... how to fix? Be brave. Be positive. Try these steps:

1) Ignore the Bentleys' manual when they say do not lubricate the "flocked" drive cables. Use a good silicone spray, the cables are nylon-sheathed and a non-hydrocarbon lube should be OK, and it makes them easier to move for the next step. If you can, take the lid right back and look for them - they run the last 40% of the drive rails in the open, on the inside edge.

2) Remove the motor, and then adjust the lid youself for a balanced position - maybe even excercise it up and down at little, leaving it at the "closed" position without any remaining tension in either drive cable.

3) Adjust the motor to the "closed" position as well (all three items align), and then BACK IT OFF - so that even with the "play" of the cam, the switch does not close. On mine, whereas the official position was dead-on the switch about to be being triggered, backing it off meant the microswitch follower pad was about 2-3mm from the counter-clockwise edge of the cam notch.