Brake Shake....

[Diver88]

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:

You must be registered for see images attach

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.

This is actually one of the things I have discovered. The bearings are very quiet and smooth but one (passenger) has more play than it should for sure and coupled with a sticking caliper on that side seems to be at least part of the problem, Thank You, I'll read the information... I'm sure it'll be helpful.

 

[Diver88]

I (and a few others) are running Raybestos EHT369H. They're doing great on both of my '97s, JB5 and JB6 brake systems specifically. Very aggressive friction compound (HH DOT rating), more so than any other offerings I've been able to find. More info here, the good stuff starts on page 5:

https://www.gmt400.com/threads/ebc-yellowstuff-brake-pads-worth-it.47903/page-5

Thanks, this will help to know. Last garage was supposed to use all Raybestos, but who really knows?

 

[Diver88]

- Here's an example of a front suspension variable that can easily checked/eliminated from the list -

When troubleshooting pulsating brakes, we will get out the dial indicator and look to see if the
rotor is still within specification. And it's just a handful of thousandths allowed. But what if
the underlying wheel bearings aren't adjusted to run within specs? Will a set of wheel bearings
mis-adjusted and running too loose exacerbate the reaction caused by applying brake pads to
a slightly less than perfect brake rotor?

'96 C/K Service Manual, Vol. 1, p. 291 in the .pdf

You must be registered for see images attach

Am I predicting that this is the root cause? It's possible, but then again it could be one of
several competing possibilities. The point is, everything in the front suspension will need to be
inspected/verified to this level of detail *before* we start throwing parts in the general direction
of our troubleshooting suspicions.

If anyone reading this has fixed a brake issue by eliminating one or more worn front suspension parts,
then please share your experience.

Just a little more food for thought...

EXACTLY, and this very well what we might have discovered. Thank You very much !!