An inexpensive fix for convertible top cover motor problems

Mike Reily, October 7, 2012

I have had my 1999 328 convertible for going on 4 years now. It is my daily driver and I love it. This year, I started having some fully automatic top failures. These all had to do with the storage compartment cover motor making grinding noises on raising or lowering, setting an error code and requiring manual override. I did a lot of research and had almost decided to convert to a fully manual top. However, after reading some of the write-ups I found primarily on this board and taking the cover motor in and out several times, I was inspired to make the fix and keep the fully automated to operational. This situation has been documented already (see http://forums.bimmerforums.com/forum/showthread.php?t=1584458) what happens over time is that the large amount of torque that the motor applies to the lever arm that raises the cover causes the motor/transmission assembly to bend. This is exacerbated when the cover movement is hindered by, for example, rubbing on the top during operation. When it bends enough so that the motor gear is not fully engaged with the transmission box, the gears make the grinding noise and the cover fails to open or close, setting an error condition and requiring a manual reset. I removed the motor assembly (Figure 1) and straightened the mounting plate that was clearly bent (see Figures 2 and 3) several times.

Each time it fixed the condition, only to have it return after a few more opening/closings. I tried to straighten the actual transmission body in a vice after separating it from the motor by driving out the hinge pin (see Figures 4 and 5). Again, that helped, but it was only a temporary fix. A new motor assembly is several hundred dollars and used ones - well, the chances are high that I would be buying the same problem I already have. So, I took an idea suggested by apatrizi in the above bimmerforms post and came up with a simple and inexpensive fix which has held up for 3 months and much longer than any of the repairs I have done so far.

Since the problem is that the motor is no longer held tightly to the transmission by the flimsy plate and hook contraption that are clearly seen in Figure 3, I tried using a C-clamp to hold them together temporarily after one of my remove/straighten/replace operations. That seemed to work well but of course looked like crap and would not allow me to put the trunk liner back over the motor assembly. So, I bought a cheap 2-1/2” C-clamp, cut the handle off and cut a slot for a screwdriver in the stub of the handle to lower the profile of the clamped assembly, see Figure 6.

The clamp basically squeezes the motor (on the left in Figure 6) tightly against the transmission (in the center of Figure 6 and obscured by the black metal mounting plate). This eliminates the gap that develops between these two parts when the motor mounting plate becomes bent. It is important to make sure that the placement of the clamp does not interfere with the operation of the top lift actuating lever. In order to keep the back of the motor body from being damaged by the clamp, I reinforced it with a scrap piece of steel plate I had laying around, using double sided foam tape. You can see this in Figure 7 and 8.

Obviously, one could to a prettier job of cutting this plate, but it is not visible once the motor is installed, so I did not spend too much time on it. Figure 9-10 show some more views of the modified clamp attached to the motor/transmission assembly.

Figure 11 shows what it looks like installed in the car.

With the trunk liner up, you don’t see any of this. If I ever need to release the motors via the emergency release cable, all I have to do is first remove the C clamp with a screwdriver. I hope this helps keep a few convertible owners happy with a few more bucks in their pockets!

Useful references

Pelican Parts Convertible top information: http://www.pelicanparts.com/bmw/techarticles/101-Projects-74-Convertible/101-Projects-74-Convertible.htm

Resetting convertible top: http://forums.bimmerforums.com/forum/showthread.php?t=564247

Zack on YouTube - nice video on resetting semiautomatic top: www.youtube.com/all_comments?v=boiybaJkMrI