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The Mystery of the Sunroof

Pelican Parts has a great article on the care and repair of your sunroof.  Take a look here.  This article is meant to provide additional information.

Porsche put sunroofs in most of their 924 and 944 cars.  Unlike the earlier 911 sunroofs that retracted into the bodywork, these sunroofs are hinged and removable – quite archaic by today’s standards.  And they often don’t work as designed.  Here we will look into the sunroof, its operation, and what normally goes wrong with them.

The tilt sunroof in early 924 cars was a manual operation – undo the latches, push it up in the rear, and it was tilted open.  Undo two more latches and take it out – the good ol’ days.    With the 944, we got the electric sunroof – same concept but electrically powered.  And with age, lots of problems.

microswitch.jpg
The Dreaded Microswitch

Today we depend on sensors and computer chips for things like this, but “back in the day,” these modern marvels weren’t available.  Like the complex Ford hardtop/convertible of the fifties, the mechanisms are powered by cables, motors, microswitches and gears – and can fail.  Timing all these things is where failures and damage can occur, and the microswitches are part of the problem, but I’m getting ahead of myself.

There is a sunroof button on the console.  This button allows you to open and close the sunroof, but also allows you to release the sunroof latches so that you can take it out. That button activates a motor mechanism in the left rear of the hatch area, behind the carpeting and a protective cover.  The mechanism is attached to a screw-like cable which is pulled and pushed to activate the latch/lift mechanisms in the roof.

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Sunroof Gear

One of the most common failures occurs in the latches in the roof.  The cable engages a nylon gear in each latch, spinning it and driving the latch up and down.  When something goes wrong, this $10 gear is the failure point – nylon vs. metal.  The nylon gear teeth shear off, and the mechanism fails.  You can hear the motor running, but nothing happens.  These replacements are readily available from many of the vendors on our Vendor and Information Page.

Replacing this gear isn’t very difficult, but it can be challenging to access.  The rear sunroof gear cover across the back of the headliner has to be removed to get access to the mechanisms.  You will then find the two latches; take the cover off with the five phillips screws, and there you will find your broken gear.  Take it out along with the sheared teeth that are probably trapped in the grease.  Replace it with the new one and put it back together.

BUT WAIT!  The situation that existed that led to the failure of the gear may still exist!

There are many reasons why these gears strip out, and I will not go into all the reasons here.  Instead, we will troubleshoot the system and see where the problem may be.

With both latches disassembled and the lifting arms removed, you should see the screw cable running through both latches.  Work the switch to see that the cable is turning and that it stops by itself.  There are two failures that you may see here.  (If the cable moves back and forth and stops on its own, all is well!)

  • The cable is not visible in the latches – it isn’t there!
  • The cable will not stop on its own.

Either of these conditions indicates that there is a problem with the motor mechanism in the hatch area, and both indicate an issue with timing or with one or more of the microswitches there.  When you activate the switch on the console, the motor turns, pushing the cable one way or the other.  To keep the cable from going too far, the microswitches override your console switch and stop the cable at certain points.  If a microswitch has failed to stop the cable, it can unwind it out of the casing and into the bodywork in the hatch area.

If you find a bundle of screw cable in the left rear around the motor, there is a problem.  Remove the motor mechanism from its mounting (don’t try to take it out of the car completely!) and look for obvious faults.  You can feed the cable back into its housing and into the roof, through the latches pretty easily.  A small amount of waterproof grease may be indicated if the cable is dry.

After you have fed the cable back where it belongs, have someone activate the console switch and watch the mechanism to see what happens.  It is is operating normally, it should move the cable a few inches in each direction and stop on its own.  If it does not stop on its own, there is a problem with the microswitches or in the alignment of the switches.

With someone operating the console switch, try to shut off the mechanism by manually operating the microswitch – it could easily be that one of the the switch mounting screws is a little loose and threw the switch out of alignment so that it doesn’t make proper contact and work as designed. Align it so that it makes contact when it should, tighten everything up, and give it a test.  (Remember that there are three of these switches.  Check them all.)

If one of the switches does not work, replace it – they are cheap.  While they are not necessarily prone to failure, I keep a few extra in my box (next to the spare gears!)  Test it to ensure that the screw cable is working properly and stopping on its own at each end.  (The cable NOT stopping is when it strips the teeth off the nylon gear.)

When you are sure that the cable mechanism is working properly, the next step is to set up the timing for the lifting arms.  With the key on, work the console switch so that the screw cable moves towards the driver door and stops on its own.  This is the “down” position.  With the sunroof in and down, install the new gear in the latch with a little grease, then the lifting arm.  Position the arm so that it catches the sunroof and holds it down – you may need to move it one or more “teeth” to ensure that it holds the closed sunroof tightly in the down position.  Repeat for the other side, installing the covers.

Test it carefully, listening for any strange sounds – remember that these are old mechanical systems with many failure points.  The motor should lift the sunroof and stop on its own, then retract the sunroof and stop in its own with the sunroof down and sealed.  If a small adjustment is needed, there is a knob on the motor mechanism in the hatch area where you can adjust the cable.  Only small adjustments should be needed.

The real test comes when you want to remove the roof.  With the key in the first position, activate the console switch.  If all is well, the lifting arms will retract completely into the bodywork and stop on their own, allowing you to remove the roof.  When replacing it, just put it back into the hole and activate the console switch.  The lifting arms will move back into position, allowing you to open and close the tilting sunroof.

A word of caution – take the time to look everything over and understand how this mechanism works.  It will go a long way.

Some folks just want to lock the sunroof down and never open it.  For them, you can make sure that the screw cable is present in both roof latches, put in new gears, and position the lifting arms so that they are holding the roof closed.  Reassemble everything, use the knob on the motor in the hatch to make sure that the roof is down and tight, and unplug the sunroof motor.  This works.

Kevin Duffy, Author and Chief Geek View All

Kevin Duffy is an Associate Professor of Criminal Justice at Daytona State College in Florida and a dedicated car guy. He divides his time between teaching criminal justice topics in the online environment and working on/driving cars, particularly Porsches. Kevin is one of the principals in InspiringLifeOver50.com.

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