Sunroof Gearbox Stiff - Can it be Overhauled?

[OZCarrera3]

My sunroof ceased operating recently, so I have been working my way through the possible causes. I know the switch is working and that the motor is working (after taking the gearbox out). What is apparent now is that turning the gearbox is quite difficult. The mechanism seems to be very tight and hard to turn with a screw driver, like the grease inside has gone hard or something.

My question is can these units be pulled apart, cleaned out and then re-lubricated? The backing plate seem to be held in by the edges of the casing that have been pressed over the edge of the backing plate.



My guess is that this is a replacement rather than rebuild fix - not very appealing thought as the gearbox is $530+ from our host.

[sc_rufctr]

At $530 for a new one I would certainly try and fix what you have.

I haven't had to do this on my car so I'm not much help but...
There are some talented guys here who should chime in soon.

Up for more views.

[stevie 77 930]

Yes they can be overhauled... Remove the gear on top. Carefully pry away the tabs to remove the cover. This will reveal the gears and the glue-like grease that has aged. Carefully clean out all of the grease and spray liberally with brake cleaner. You should notice that the gears move freely. Apply new grease....here's where a little goes a long way. When completed, I used a silcone adhiesive to seal the top back together. Put it on c-clamp overnight to cure. I carefully pinched the tabs back just a bit and reinstalled. Good as new for the last couple of years

[OZCarrera3]

Thanks for the advice Stevie.

I had actually come to the conclusion "I have nothing to loose" overnight, but its good to know that someone else has tried and been successful. Thanks particularly for the advice about sealing the case at the end, I had not thought of that and had intended to just close it up (which would obviously result in leaking grease on hot days and/or dust/dirt entering the unit).

Love this forum!

[aadrew10]

I did this one month ago. Everything was frozen and after removing each part, shaving off the dried grease with a blade, and re-lubing it, works as good as new! You'll have to re-tune the clutch adjustment of course.

Keep everything in order as you take it out. So easy a mechanic can do it!

[OZCarrera3]

Aadrew,

Last night I pulled the gearbox case apart and cleaned out all the old grease. The drive shaft was still very stiff, so left it overnight to soak in cleaning fluid. Its much better this morning, but still a little stiffer than I think it should be and after working it a little, will leave it in for the rest of the day. I'll post a full pics/description on this thread when complete the re-lube, re-installation and I know it works.

Also, how do you "re-tune the clutch adjustment" and where is it?

[aadrew10]

Sheldon,

The clutch adjustment is the flat head screw that tightens what I'll call the main shaft. The main shaft is the shaft that goes through the large gear, and the clutch plates. If you keep it fairly loose, you can turn the 'input shaft' without the main shaft moving. Anyways, keep that snug, and after you get everything installed, try and open and close the sunroof. If it will not open and close, tighten the screw a tiny bit until it opens and closes. The purpose of tightening the screw in increments is so you don't over tighten it and start putting extra stress on the cables and gears. The object is to get the sunroof to close completely with the loosest clutch setting.

Interesting thing happened to me when I was trying to reassemble the assembly. I could not get the bushings on each side of the main shaft to line up perfectly. The main shaft would turn effortlessly if it was installed in the top and bottom bushings separately, but once I put everything together and pressed in the cover plate thingy, they went out of alignment. I was pretty upset about this, but when I put it in the car it magically became easy to turn. If this explanation is hard to understand, it's not that important anyways.

Have you taken the main shaft completely out, or are you just cleaning what you can see?

- Andrew

[kolies]

I had the same issue with mine. My car sat out sire for 6 years before I bought it. First project that I did was tear apart the sunroof (there were repair records in the glove box that it was very slow).
The input shaft was very hard to turn. I took off the little metal plate above the worm gear, and scooped out as much of the old grease as I could. (I was going to take the bigger cover off, but didn't want to uncrimp the casting, and take the chance that it wouldn't stay together after re-assembly.) I applied new grease to the big gear and kept on turning the input shaft by hand to distribute it. It got better, but was still very stiff. The thing that made the most difference for me, was when I dripped some of the Magnum Teflon lubricant into the worm gear bushings (it could probably be any lubricant, like Gibbs potentially as well). I kept turning the input shaft by hand, and it loosened right up, and spun very freely. A year and a half after I did it, it still opens and closes very easily.

[OZCarrera3]

Thanks for the continued help Andrew.

Please confirm my notations on the following picture. Unfortunately I am at work at the moment and do not have access to my photos of the open gearbox.



You are correct, I have not removed the main shaft from the housing as yet. I was going to see how well soaking the unit in cleaning fluid works on loosening up all that old grease first.

Assuming this does not work, how did you get the mainshaft out from the bushes out? I remember seeing two small allen screws or pins (?) on either side of the top bush, but nothing on the bottom (from memory).

[aadrew10]

Our names for main shaft and input shaft are switched. The shiny yellow thing in the picture is just a cover that you should be able to pry up if you haven't already. I did not remove what I call the input shaft. If you are going to remove the peened cover after taking off the cable gear, I would suggest you grind out the peened sections so you don't bend that cover. If the cover gets bent the bushing will not line up nicely with the shaft and the bushing on the other side of it. Removing this cover is the only way to get the internals completely clean and re-lubed. Soaking may be enough though...

- Andrew

[OZCarrera3]

Ah yes, got the names around the wrong way sorry.

I have already taken off the cover, unfortunately not by grinding them as you suggested. Hopefully I have not warped the housing.

The input shaft (as you rightly describe it) is the one that is hard to rotate in my unit. I feel more comfortable now that soaking it will "loosen" is up sufficiently.

In re-reading your earlier post about the clutch, I am sure this has been one of the main problems with my sunroof, along with the dried-out grease. Since I've owned the car, the sunroof has always made a grinding noise when at full travel in either direction. To stop this, I just released the switch the moment it started to make the noise. I had wrongly assumed it was some sort of override release mechanism, but clearly the clutch has been too tight and was not releasing the drive on the main shaft. I will make sure to adjust it as you've advised.

One nice thing is that even though this is a sealed unit, the internals are all metal as opposed to the plastic they would make them out of today. That main shaft drive cog for example is beautifully made. It appears to be a cast aluminium wheel with a brass ring and teeth pressed on to its circumference! After 33 yrs of use, mine still look like new.

[aadrew10]

After overhauling mine, the cables still grind if I hit the open stop. If I loosen the clutch, then it doesn't close. Now, I just watch the sunroof as it opens and stop it about a half inch to an inch before it gets to the open stop. No sense grinding the cables further.

- Andrew

[Forza]

Originally Posted by aadrew10

After overhauling mine, the cables still grind if I hit the open stop. If I loosen the clutch, then it doesn't close. Now, I just watch the sunroof as it opens and stop it about a half inch to an inch before it gets to the open stop. No sense grinding the cables further.

- Andrew

I was having the same problem. When I rebuilt my sunroof tranny, I replaced the sunroof pinion gear (928 564 125 02; $17). Comparing the two, the older gear's teeth were worn. With the new pinion gear installed, my sunroof has worked perfectly. Visually inspect the rubber clutch coupling (between the tranny and sunroof motor) while you're at it to ensure it's not deteriorated.

[78 911SC]

Time to dig up an old post:

Andrew above talks about tightening the clutch in the transmission:

"The clutch adjustment is the flat head screw that tightens what I'll call the main shaft. The main shaft is the shaft that goes through the large gear, and the clutch plates. If you keep it fairly loose, you can turn the 'input shaft' without the main shaft moving. Anyways, keep that snug, and after you get everything installed, try and open and close the sunroof. If it will not open and close, tighten the screw a tiny bit until it opens and closes. The purpose of tightening the screw in increments is so you don't over tighten it and start putting extra stress on the cables and gears. The object is to get the sunroof to close completely with the loosest clutch setting."

Can someone please post a picture of this?

My transmission does not have the screw that he states and my transmission just does not seem to have the power to close the roof.

I've already removed and cleaned everything so with the transmission removed I can easily slide the roof back and forth. The cables and all other parts are intact and work fine (rubber clutch, motor, transmission is in smooth working order).

If I run the roof with the switch and at the same time put my finger up against the pinion gear that is connecting to the cables I can feel it stop moving...which leads me to believe that the internal clutch in the transmission is slipping.

And about this screw: what size is it and can I just go and pick one up at the local hardware and install?

Thanks!!

[78 911SC]

bump

[aadrew10]

It's been awhile but I I remember correctly its a large flat head screw right in the middle of the gearbox assembly. Does yours have a hole instead of the screw? I would take a picture for you but I'm on a long trip out of the country. Maybe someone else will send a shot? It only involves unzipping the headliner...

[78 911SC]

Yes, I just have the threaded hole instead of the screw.

I can't seem to get how this could solve the internal transmission problem, because it's just a simple thread. How does it help to engage the clutch?

Here's a pic of the hole in the transmission (larger hole in the middle):

[aadrew10]

Yeah you are missing the screw. The screw squeezes the clutch discs together. Try and figure out what thread it is. Take it to your local hardware store and try a few. As long as it is not too long it should work.

[78 911SC]

Thanks! Should the head be wide enough to cover the entire top, or fit inside the opening?

[78 911SC]

Also, does that mean the screw should be a tight fit?

I did try a 5mm screw from Home Depot (I believe that was the size) and it felt tight...the size on either side of that was either too big or too small.