[apex]

Well this weekend I'm upgrading to Robby/IceShark cables and a new alternator. Last weekend was a sunroof fix (more on that below). That means to get to Maintenance Backlog Zero all that's left is

• hatch glass
  
• paint repairs (don't ask!)
  
• rocker panel rubber
  
• passenger door latch
  
• motor mounts
  
• oil change
  
• coolant slow leak
  
• etc and so forth and so on 
  

Humor aside I thought it would be useful to post what I learned replacing a stripped sunroof gear for the second time. First time was about five years ago.

 

If you're familiar with the geometry of the sunroof struts, you know that the struts engage the sunroof through a slotted fitting such that if the strut is withdrawn all the way you can take the sunroof out, if engaged just an inch or so, the sunroof is locked down, and if engaged more than that first inch, they start to push the sunroof up.

 

And the google tells us that mysterious failures of this mechanism remain even when folks have otherwise adjusted everything to spec.

 

The driving mechanism uses slotted holes to bolt it to to the roof, allowing for adjustment by sliding the entire gearbox forward or back. The failure mode I discovered is, in my early '92 car, the gearbox could not be slid back far enough to allow the strut to easily slide into the sunroof slot - the strut ends up being too low relative to an ideal path of travel. So every time the sunroof is closed, the tab needed to FORCE its way into the too-high slot through to the "lock" position which really clamped down the sunroof as it attempted to get in there.

 

So... lots of stress on the gear - eventually it gave up the ghost.

 

The remedy is to remove the plastic gear mechanism from the car - four bolts - and extend the slotted holes in the right direction to allow the gearbox to slide back the additional 3/8" inch or so. I used a drill bit that matched the ID of the hole and just let it chew back into the plastic a bit.

 

Once this was done it was very easy to adjust gears and struts, check alignment, and bolt it back up. The struts now slide into the sunroof slots with hardly any resistance at all... just enough to keep the sunroof tight at speed. 

 

And yes, my sunroof was adjusted all the way down already (the plastic adjusting screws in the sunroof gutter). Seems like a case of slightly-wrong build dimensions out of the factory.

 

Cheers.

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[Peter B]

When I bought my car, I was told by the prior owner to either crack a window or crack the sunroof open if I was planning of going over 100MPH.  I think the quote is "that's why all the sunroof gears keep getting stripped".   

 

My understanding is that the difference between the cabin and outside pressures becomes too great and the poor little gear just pops.  

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[apex]

Haha! So that's the problem - I need to keep it under 100mph!

 

My guess is that the relatively mild negative pressure would not strip the gear. The force from driving fast will pull UP - before I fixed my gears one side of my sunroof was loose and would predictably open itself at 70+ mph.

 

The design of the gearbox is such that upward forces are 90 degrees to the mostly horizontal strut - it slots into the housing of the gearbox and the stiffness of the steel strut holds the sunroof closed, not the gear teeth. The gear only pushes and pulls the strut forward and back. It's hard to explain without a diagram but the gear pushes the strut horizontally - the strut is slightly curved and the clever geometry of it all causes the horizontal movement of the strut to cause the roof to go UP.

 

Of course on the other hand you might be right. :lol: How many pounds of up-force at 100 mph do you think?

 

J

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[ds968]

I'm very skeptical of that theory.. I've taken my six speed on multiple occasions past tne 150 mph mark , and furthermore I lost count of how many times I've driven it at 120 -130 mph + ( at least a couple of hundred times though.. ) and never had a problem with the sunroof gears. I seriously doubt you can build enough cabin pressure to strip tne gears when the roof is closed unless you take your car into outer space , lol. On the other hand my daily driver which hardly sees triple digits has stripped gears. Go figure. :-)

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[Bulti]

Apex - I've got to ask: have you checked the torque of the sunroof motor?

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[apex]

Bulti - yes I methodically checked each part of the system. Torque is now set low per Clarke's Garage recommendation - about 5 nm. Ha - it's really marvelously complex our sunroof mechanism. I have to believe a squad of over-achieving German engineers stayed up late many nights coming up with this Rube Goldberg machine and made it as complex as possible just to have some fun - limit switches, rotating cams, torque slip-clutches, worm-drive and toothed gears, micro-switches, cables, shafts, down-buttons that go up, up-buttons that go down... devilish.

 

I am very confident that on my car, at least, the gears are now operating in an un-stressed mode. Of course, having just said that I've jinxed the whole pooch and now they will strip tomorrow.

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[Bulti]

Lol, just stripped a gear a few days ago. I replaced them about 5 years ago. Sounds familiar? Guess a trip to Clark's is in order ;-)

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[az968]

So I think I just stripped the gears. The car was standing still, tho, not at 100 mph+. I re-installed the sun roof and the arms go only part way up into the rear roof receiver latch and stop, I can hear the motor running but the arms don't go far enough into the sunroof receiver latch to "lock". Does that sound like stripped gears?  If so, to get to the mechanism, is it just a matter of removing the 7 screws (covered by trim caps) and the roof panel behind the sunroof drops done for access?

 

Good think the weather is still good so I can drive the car with the sunroof out. But winter is fast approaching.....

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[Bulti]

I'm not completely sure anymore, but I think you need to loosen the roof liner too.


Definitely sounds like stripped gears.


If you replace them, make sure to adjust the torque of the slipper clutch, or you'll be doing the same job again in no time.


Check Clarck's for the procedure.

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[az968]

So I just had to remove the roof panel behind the sun roof to get at the latches and gears. I found one gear with one missing tooth. The other gear looked fine but I ordered 2 new ones. I don't think that was the cause, I would think the one good gear, and even the one with the missing tooth, would still move the lifting arms. I'll check the slipper clutch when I reassemble the lifters.

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[Peter B]

Back to the 100+ MPH popping the sunroof theory.  I believe it now, based on ....  

 

My sunroof has been solid - no problems.  I got on the freeway today with a pretty big head wind, tossing the car around.   I'm going ~ 80.  The wind is likely ~ 40.  The car is making funny noises that I haven't heard before.  Like whistling around the edge of the windows but somehow stranger - almost from the interior.  Then, pop.  The passenger side of the sunroof goes up (un-even).  $%*& (I might add).    Was there so much build up of pressure in the cabin that I was hearing air getting forced out of the weather stripping???  

 

The roof still goes up and down, but won't close all the way on the Passenger-side.  I hoping I can take it out and put it back in - that that will line it up. 

 

Wind speed + car ~ 120.  Note, if you're going 150MPH, are any of your windows or sunroom open?  are there any open vents to the exterior?   Even if the door panels are removed, there is your vent out the bottom of the door (rain drain).   Maybe the weather stripping is shagged?   

 

Let me know if there is anything else I should do about my sunroof.  It's supposed to rain tomorrow.   Yikes. 

 

Now I feel I have to worry about my speed and combined with the wind - it's really windy in the Columbia river gorge.  BTW, I was going windsurfing - all the gear, 8ft board included, fit in the car.  968 rock and occasionally pop.     

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[Peter B]

So, the passenger side jumped the rail when in that wind plus speed ~ 120 MPH.  Nothing broken.  The wind had to be pulling hard!  FYI - over 100MPH.  

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[Rap]

I have not had sunroof problems with two track cars at speeds up to 135. Can't say at high speeds that I can or do hear wind noises because I'm listening to the engine, other cars and tires depending upon where I am on the track.

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[Peter B]

Yes, but is your track car sealed up?  Door panels off? Then not sealed.  You probably have your windows down - at least you should.   My point is, crack your window before your foot goes down (non-track car). 

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[Rap]

I've had my queen up over 100 closed up no problems. Maybe I'm not going fast enough!

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[unknown4u]

Flat out no problem over here.

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[dlearl476]

Bulti - yes I methodically checked each part of the system. Torque is now set low per Clarke's Garage recommendation - about 5 nm. Ha - it's really marvelously complex our sunroof mechanism. I have to believe a squad of over-achieving German engineers stayed up late many nights coming up with this Rube Goldberg machine and made it as complex as possible just to have some fun - limit switches, rotating cams, torque slip-clutches, worm-drive and toothed gears, micro-switches, cables, shafts, down-buttons that go up, up-buttons that go down... devilish.

 

I am very confident that on my car, at least, the gears are now operating in an un-stressed mode. Of course, having just said that I've jinxed the whole pooch and now they will strip tomorrow.

A VW Beetle has 4 or 5 moving parts between its accelerator pedal and the carburetor. When I was rebuilding my 912 motor, I counted 68.

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[az968]

My 996 accelerator runs on electrons. I think I'd prefer the moving parts for ease of trouble shooting.....

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