GMT400 Vibration Troubleshooting A-Z
Schurkey's reply is what prompted me to write #35 last night. I'd like to add a couple of short comments that
didn't make it into last night's tome.
Re:
1. I found the 'hard braking fixed problem temporarily' interesting. Getting disc brakes that hot =
a *lot* of radiant heat is being thrown from the rotor. (Where we turn the truck's kinetic energy into
thermal energy.) Wheel bearing grease is specially formulated to withstand temps up to 475° (F) without
breaking down for this very reason. (
Hi Temp wheel bearing greases) Given this, which part(s) would tighten
up with this amount of localized heat, removing excess play, and temporarily solving the vibration issue?
Re:
4. I completely agree with this thought process. Anyone reading this who's pushed a shopping cart
around (where the front wheels have negative caster & experienced all kinds of wobbly vibration) has a
glimpse of how the twisting forces associated with clamping brake pads onto a spinning rotor might
take a stable suspension system (with excess play somewhere) and dynamically reduce the caster angle,
creating momentary bad geometry that's more susceptible to vibration inputs?
****
To prepare yourself for the next level of vibration analysis, I strongly recommend that you
read the chapter on Vibration Diagnosis and Correction in the Factory Service Manual.
More specifically, this section seemed to get stronger over the years, so by the '99 C/K
Service Manual it is a great read.
And here's where you can obtain a free download of the '99 Service Manuals:
(
LINK, tip of the hat to
@PM18S4)
Note: You could just download the file with Vol 1, open it up, go to page 94, and check it out.
Here's the start of that section:
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Anyway, between all of the above the answer is hidden in there somewhere. :0)
Happy Hunting! And please be sure to let us know what you discover -- this way
we can all learn from your experience.