In the July 2007 issue of Roundel, I wrote a column titled “Walking in Hack Footprints,” in which I described addressing a window issue in my then-recently-purchased 1999 M coupe. The driver’s-side window was making a metallic banging sound when rolled up to its highest position. I’d taken off the door card and found, with some degree of horror, that a previous owner had jigsawed a section of the door out, taken a slightly larger sawed-off section from another door, and bolted the latter on top of the former. Then I found that the regulator had been modified: Another hole had been drilled in the rearward-facing section and bolted to the back inner edge of the door in a rather odd manner.

Not knowing what the problem was, I decided to order a new regulator, which at the time cost only about $85. While going through the process of removing the old regulator and installing the new one, I realized that the reason the door had received this odd surgery was that the welds holding the bracket that holds the regulator had broken; they’re very difficult to reach and re-weld because they’re inside the door, and the bolted-in section was there because it contained a bracket from another door.

I initially regarded this the way you would if you bought a house and found the previous owner’s crazy uncle living in the attic—at least that’s how I regarded it until I found that the root of the problem was that some of the welds in the bracket in the bolted-on section had also broken. I quickly realized that its removability was no longer a kluge; it was in fact a highly-desirable feature: I could simply undo the bolts and take this piece from another door into a welding shop to be re-welded. And fourteen years ago, that’s exactly that’s what I did.

The slot cut into the regulator was also a genius hack, and I wound up having to do exactly the same thing to my brand-new regulator in order to get the back corner of the window to tuck itself neatly into the corner of its gasket.

Fast-forward to last week. I’d been driving the clown shoe quite a bit, as I still hadn’t put the time into doing the delayed maintenance on the 2003 E39 530i stick sport. At some point, the M coupe’s driver’s-side window had begun banging when I rolled it all the way up. This almost literally rang a bell: I dug out the old article, pulled off the door card, and came face-to-face with that which had vexed me fourteen years ago.

Hello, crazy old uncle. What are you doing out of the attic?

I unbolted the hacky-yet-effective workaround, examined it, and this time found the welds intact. Hmm.

I re-read my original article carefully. It said, “Typically, this banging on roll-up is caused by a broken window-regulator clip. These are white plastic sliders that form the mechanical interface between the window regulator (the Rube Goldberg-looking thing with gears and arms) and the window itself. The regulator has posts that snap into the side of the clips, and the clips slide back and forth in a short horizontal section of track at the bottom of the window. If both clips fail, the window won’t roll at all; but if only one fails, the window twists, and the current-sensing mechanism that usually stops the motor keeps trying to roll the window higher—hence the banging.”

I think I got it wrong years back when I talked about a “current-sensing mechanism.” I believe there’s a Hall Effect sensor in the window motor that detects rotation, and thus knows when it’s ceased.

But I also said that after replacing both clips, the window wouldn’t roll up more than a few inches, and I couldn’t figure it out, so I took everything apart, replaced the regulator, and greased all the tracks. This was a mistake: I believe that the window motor can lose its sense of where the top and bottom are if the battery is disconnected, and I was disconnecting the battery in order to avoid setting off the air-bag light. (There is a method to re-initialize it.) It’s possible that I unnecessarily replaced the regulator fourteen years ago. But then again, when I was done, I had a window that was no longer banging, so who knows?

Hmm a second time.

I checked online and found that, unfortunately, the window regulator now costs about $235, substantially more than the $85 it was fourteen years ago. I’ve been spending money like water recently on maintenance on a bunch of the cars, and wasn’t sure that I wanted to drop it here when I wasn’t certain that it was the cause.

It took a while, but I was able to see where the banging was coming from: It’s part of the window regulator rhythmically snapping up and down over the crash reinforcement bar in the door. Why it began doing this now, after years of silence, is still a bit of a mystery.

The smoking gun—which is almost what it sounds like when it bangs.

One of the dynamics that plays out frequently these days is that with my garage full of must-keep-out-of-the-weather vintage cars, I’m hesitant to kick one of them to the curb in order to shelter a newer car whose repair may stretch out over several days (and, I’m ashamed to admit, the M coupe has been sitting outside). And if I remove the window and the regulator in the M coupe, there seems little choice but to do that. Plus, I’ve got a number of irons in the fire: I’m still putting time into the E39 (I’ve refreshed the cooling system, and am about to do the same with the fuel pump). Our little RV needs more maintenance before its next long-summer-weekend jaunt.

And I just bought a truck (a long story you’ll hear about).

I’m not sure that I want to continue to play this hand with the M coupe when the window still does in fact roll up and down. Years ago, in a different Roundel column, I said, “Look the beast in the face. If you’re not prepared to battle it to the death, back slowly out of the cave.” Granted, this is a very small beast in a very small cave, but I took the coward’s way out: I bailed. I buttoned things back up.

The M coupe has been here at the house since I loaned it to Magnus Walker for that video shoot in early May. I typically cycle cars back and forth to my outlying storage area in Fitchburg every few weeks, and I’m overdue. I think that I’ll order a set of window-regulator clips and try installing those, because if memory serves me correctly, that’s a quick hit-and-run repair that I can try without completely disassembling the door. If it works, great; if it doesn’t, I’ll leave the mystery for another day and let the clown shoe sit out in Fitchburg for a bit.

So yeah, this week’s installment ends with your intrepid Hack being a bit of a wuss. Next week I shall endeavor to be daring again.—Rob Siegel


Rob’s new book, The Best of The Hack Mechanic, is available here on Amazon, as are his seven other books. Signed copies can be ordered directly from Rob here.

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