BMW E53 Door Handle Carrier fix

These door handle carriers (on the BMW E53) are notorious for failing frequently. It's not only from "user error," pulling too hard on the handle; the carrier is just horribly engineered. No wonder BMW improved the handles for the later models. 

This is a replacement carrier. My old carrier broke at the red line below:

There are two major problems with the design:

1. The geometry of the carrier creates a mechanical advantage of 5x near the point of the arrow in the photo.  If you pull with 5 lbs (which can happen easily when pulling on the handle with body weight, as some folks do) then there's 25 lbs of force on the tiny teeth of the "gears" that pivot a bar to pull up on the cable.  Then, the mechanical advantage reverses to mechanical disadvantage due to the length of the bar that pulls the cable up. Thus, even though the cable moves about 0.8 times the distance that the handle pulls, the force gets amplified 5 times, then reduces to about 1/4. An ideal design would only increase the force by 1.25x on any component; that's the force that is applied to the cable pull.

Also, there is friction in many places (like in the cable itself), that only increases the force required to pull, which in turn increases the force on the weakest parts. It's a wonder that this carrier lasts as long as it does.

2. There's a little rubber stop for the handle movement, but it's not good enough to stop a strong pull from flexing things and causing the moving part to press (with 5x force) at the point of the arrow. When you have it in your hands, you will see it happen. It should not press at that spot at all! So, it broke at the red line.

HOW TO IMPROVE IT

The solution was to get a new carrier (obviously), and file away some metal on the moving part (I used bits of sandpaper; that was the only way to reach in between the two parts). It took a while to file away enough metal (but it's ok because the moving part is thicker than the thin part that broke). The technique is to cut a piece of sandpaper small enough to fit in between the two parts that touch, insert it rough side toward the stronger moving part, then move the handle so the paper is squeezed, then slide the paper out. and do this 100 times! With a little practice, you'll be able to scrape away a little metal on each pull without tearing the sandpaper. I sanded away bit by bit until the sandpaper wouldn't get "grabbed" in between the formerly touching pieces. (Clearly, this carrier was designed to only withstand "just enough" force to open the latch gently. Good luck with that!)

Hopefully, this will be the last time I have to replace this particular carrier.

ANOTHER ISSUE

On my 2005 E53 X5 (front passenger door) I found there's a piece of rubber that gets flexed when the door handle is pulled. WTF? This just adds extra resistance and serves no purpose that I can see. So I cut off the lower part of it with a razor blade. Tough to reach that spot, even with the carrier removed.