Saturday, August 30, 2014

A Missing Knob is Like a Missing Tooth

Beside myself with excitement, I went out this morning to have a quick look at the console of the TLRP, where one of the knobs is missing.  My guess is that someone back in the mists of time turned this knob too hard one time too many, or the system that controls how the air is routed within the car just got more and more stiff over time.  

In any case, the torque of the turning action stressed out the (cheap / underspec ) plastic that lives within the knob body, causing it to crack.  The knob no longer stays on the switch stem. 

For those who are curious, the knob is composed of three pieces:
  1. A cosmetic bit that faces into the cockpit of the car
  2. A non-cosmetic bit that faces into the dashboard
  3. A little metal sleeve that prevents the non-cosmetic bit from rounding off
The cosmetic bit looks like ABS, which is a durable plastic that lasts forever - but is expensive

The non-cosmetic bit looks like PE or PP, which  is cheaper and (should be) softer than ABS

The metal bit is spring steel, and it is "keyed" to enable the knob to only be put on in the righ orientation, which is a good idea, but I think the flexing of the steel has probably played some part in weakening the stem over time.

Because the sleeve was still on the stem, another knob couldn't be put on it easily.  So I used  pair of pliers to gently slide the metal sleeve


Front view of the console knobs:










Here's a good shot of the missing knob:


Here's the console that the knob fits into:




Hmmm...here's a shot of the "good" knob, see the crack?


Here's a top view of the knob:


Here's a comparison view of the cracked knob and the good knob.  Notice how they've cracked in the exact same place?  Is it because the broken knob was used more than the other one...but the cracked one is on the way to being broken as well?


Top view of the two cracked knobs:


Closeup view of the two cracked knobs:


Focusing on the cracked knob, here's a view of the broken one:


Closeup of cracked knob:














Once everything was repaired, here's the fixed knobs BACK IN SERVICE:

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