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Old 10-26-2012, 10:52 PM
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MatWiz MatWiz is offline
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Yes. And, empirically, I think it was much harder to pound the adjuster post inward (into the motor) than it was to simply pull it out (out of the motor).

I'm surprised by the pounding (you said malet previously). Without the spring or without tension (when the cable is loose), you should be able to push and pull the black piece by hand.

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The strange thing is you'd expect the exact opposite!
That's why I called it "counter intuitive)!


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That is, the spring tension is clearly placing a force on the head of the ribbed adjuster post such that there is tension pulling it OUT of the motor - yet - it seems to stay in place (probably due to the design of the white plastic 'catch' inside the white motor tube?).
It stays in place because the cable is pulled and tensioned to its limits. I think the 'catch' is there to prevent it from going IN, and loosen the tension. Think of it like the alternator or water pump belt. They want it to always be tensioned.


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So, for whatever reason ... the post is not supposed to go into the motor as easily as it's supposed to be pulled out.
Right. Imagine you go on a big pothole and the shock causes the spring to compress? You don't want the cable to jump out of a roller. You want this to always be at maximum tension.

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Given that pushing it in apparently decreases cable tension, that would mean that it's designed to allow an INCREASE in cable tension - but not a decrease.
Exactly.


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Maybe it's a cable-stretch compensator?

Ah! So it 'is' a cable-stretch compensator. It's a self-adjusting tensioner of sorts!



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I see. It is adjusted in one place, and then, as cable tension slackens, it's pulled out a notch, to take up the slack in the cable.
Depends what you mean by "adjusted". By whom? If you mean by the spring - then yes. "We", can not adjust it in one place because the spring will always push it out, to the maximum tension, as determined by the spring expansion force.


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If that's the case, then pushing it in a few notches should LOOSEN the cable. Right?
Yes, but the spring is going to push it right back. There's nothing you can do to loosen it. You push it in to loosen the cable just so that you can reassemble it. Then when you let go of the spring, out it goes to full tension.


I think I'm getting way too much practice on this BMW window regulator!

Thanks for your help. You put a lot of the puzzle together (are you an engineer?).

>>> Electronics, and then I worked on big military radars, so there's a lot of mechanical aspects to that too. But that was a long time ago.

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Here is a photo of the regulator when I pulled it out of the door.
Notice that the cable tensioner was almost all the way in at that time.
Nice glasses....
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MatWiz
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