Hi all,

I recently took possession of a bit of a barn find, a 996 cabriolet that had been sitting for about 15 years. I have just about got the engine up to par, minus any pre-emptive IMS bearing replacement, and am starting work on the convertible top. Besides being very leaky, it doesn't go down. When pressing the button, the windshield latch unlatches, the windows roll down, and I can hear the whirring noise of an electric motor but nothing happens beyond that. The clamshell remains closed and the top does not fold (which is good cause the clamshell is closed).

When looking at various troubleshooting threads I see a lot of people are looking at microswitches, but my understanding is if the top is starting to open then the microswitches and relays are probably fine. Another commonality is using the red key to manually open the clamshell for the emergency open procedure, my issue with this is that I am 400 miles away from the nearest Porsche dealer and so do not want to have to ruin the calibration of the top as I don't have PIWIS or access to it. I will include a video if it trying to open to see if anyone might be able to spot the issue, I am guessing it is something to do with either the clamshell latch or the opening mechanism for the clamshell but I have never messed with a convertible before.


Thanks in advance.

 

Look in the 996 Forum for the 75$ PIWIS 3 thread.... Get it and get it working... you will need it .....

Then you can use the emergency procedure to open the clamshell and see why it isn't operating....Probably a broken cable....

 

Funny you mention that post, I just ordered a VAS tool based on the recommendation of that post earlier, we will see if customs actually lets it through from Aliexpress. This emergency operation will break the convertible top lock and clamshell lid drive, so I will need to have replacements on hand, correct?

 

Using the manual override I was able to open and close the convertible top compartment, and after that happened the entire rest of the mechanism works without a problem. I did notice the hydraulics are leaking but can't find the hydraulic bypass valve for manually moving the top, there is a black box on my car where the screw normally is. Picture attached below if anyone has any ideas.

So I think I have identified the problem, possibly two problems. The main problem is the black box for the cable mechanism, I noticed the bit that controls the clamshell latch cable was not moving even when manually turning the gearbox. I took it apart and the cables and gears are just fine, but there is a little square with rounded corners metal piece in the latch slide that fits into a slot in the plastic housing and prevents the latch mechanism from moving. I don't see how this is supposed to work, it seems like that piece of metal would prevent all operation. Anyone ever taken one of these apart?

The second simpler problem is when the blue motor for the clamshell spins there are outer teeth that spin but the inner square drive doesn't spin unless I turn it with the manual tool. I believe this is incorrect and I think that I can use the rebuild kit from the later models #99656167301; if anyone runs into the same issue, will post if the kit fits.

 

I'm going to provide updates for anyone in the future encountering this same problem.

The hydraulic bypass valves for later model cars is accessible if you reach through the auto-roll bar. Secondly the motor did not need a rebuild kit, if you operate the motor manually it will "screw in" that screw which will disengage the inner shaft from the motor. I took apart the inner shaft (held with pliers) and the brass screw, then used loctite and set the shaft to protrude about 5mm from the edge of the motor, it is where the teeth on the potentiometer fully engaged with the teeth on the shaft so it seemed appropriate to me. Be certain to set the potentiometer by disengaging the shaft and spinning it a tooth or two until you get to 6.2kΩ (I think, double check this value before disassembling) with the clamshell at its max open position.

Next I figured out the clamshell rack and pinion / cable drive mechanism. The part of the mechanism that controls the clamshell latch has a tooth on the bottom that is supposed to interface with this slot in the upper cable rack. This tooth had somehow broken off and was causing the little black metal piece that drops down from a slot in the latch mechanism to be unable to drop down, thus screwing up the whole mechanism. This latch mechanism is made out of pot metal so I wasn't able to weld it back together, using a tig and a rotary tool I was able to copy it and make one out of steel. I'll attach photos with measurements of it. I made sure to lube the latch cable and latch, seems to move smoothly now.

I tried to rebuild the hydraulic cylinders today, and had purchased some N4x18mm (18mm ID x 4mm cross sectional width) as per the recommendation on the thread on this forum. THIS IS THE WRONG SIZE. The piston is 18mm and the bore is 26mm so you need an oring that is LARGER than that size to fit. I have ordered some 18 mm ID x 4.5mm CS x 27mm OD off McMaster and will try those. For a dynamic sealing application, which this is most similar to but this isn't really the proper application for an O-ring as there is no groove, 10-20% squeeze is typically recommended. This will have ~12.5% squeeze so I think it'll work. Unfortunately I rebuilt all of the cylinders before realizing the seals weren't the right size...

If anyone is rebuilding the cabriolet hydraulic cylinders I will also include some tips. Don't try to remove the snap rings without drilling a hole, I nicked a rod doing this and the rods are extremely soft. Repaired it with super glue and then polished to 5000 grit. Drill a small hole right behind the ring and stick a pick or something through there and they should pop out. Also cover the rod in electrical tape before you start working on it so you don't accidentally scratch it. The seal on one of the rods had literally crumbled to bits and wasn't holding fluid so it was very difficult to get the white plastic bushing out. I ended up using 20w-50 motor oil, filling the cylinder with that, blocking off the banjo ports with a rubber clamp, and then wacking the OTHER end of the rod from the side I was trying to remove with a hammer. That finally had enough pressure to get it out but also sprayed right through the rag I had tied around the rod to absorb the oil. I would genuinely recommend a plastic / metal blast shield around the cylinder if yours is this stuck, there is oil 50+ft away in my garage and I am glad I didn't get a hydraulic injection injury.

 

Here are the photos of the old broken piece and the new piece:



The new cylinders and the new clamshell drive worked great, locks fine and the top opens with plenty of power. Just three issues left to fix now haha.

My current largest issue is that when using the button the top only opens to just passed center, right at pot 1 calibration 4 on the PIWIS, and then stops. If the top is fully opened with a PIWIS or hand then it will absolutely refuse to move (nothing at all happens when pressing the button) unless I do the calibration procedure with a PIWIS and interrupt it when the top is up. Then the buttons work normally. I read on renntech that this might be an indicator of a bad microswitch in the latch, but I tested all the switches and re-calibrated the latch and everything seemed fine. Any ideas? This one is really troubling me, I have no idea how to move forward at this point. When I try to close the top or open the clamshell from the top down position PIWIS gives the error "hardtop closed."



Photos of the potentiometer and calibration values at the point where the top stops. The clamshell lid (pot 2) is exactly equal to its cal position 4 value (should it maybe be higher than it? This is fully open) and the top (pot 1) is right around its calibration 4 value (this is 4/6 of the way open).

Other two issues are surging (hopefully a restrictor from Cabriolet Hydraulics will fix this, we'll see) and the top fabric doesn't fold right. It gets caught on the clamshell latch and seal. These are minor annoyances for now as you can just stuff the fabric back in while the calibration procedure is running...being really careful not to lose a finger. Top fabric also ends up on the outside of the trim with it closed but I figure that's probably related to the folding issue.