5ktq Brakes binding, MC? (long)

[Doyt W. Echelberger]

Sorry about the length of this thing, but I thought I should get the
details in there at the beginning.

My 87 5ktq brakes are coming on while driving in hot weather, and they are
binding enough to stop the rolling car when it is doing 3-6 mph. It is
a  typical story of a phantom foot on brake pedal in hot weather, after
about 30 minutes of driving at 70 with the AC on. Serious enough that it
will stop the car from rolling at 3 mph when I get to the toll booth. It
can and has gotten considerably worse when I got stuck in stop-and-go
traffic at an accident scene on the turnpike. It would stop the car from
5mph then, and I had to slip the clutch to keep rolling with the creeping
traffic. Then, when traffic speeded up, The car shuddered and resisted my
attempt to keep up with the improved traffic movement. I pulled off onto
the berm and turned off the engine and let it cool for 10 minutes. Upon
restarting, it ran with only minimal brake binding, which gradually
lessened as the ram air cooled everything down. After 30 minutes at 70, it
was almost rolling free at the next toll booth.

During the strongest binding, the engine temp gauge showed past half way,
near the third mark. It normally runs just past the 2d mark on the highway.

I already know about checking for a plugged cap vent hole on the brake
reservoir. That isn't it.

Also learned today about trick of pouring cold water on the MC when the
problem presents itself, and seeing if that helps. I'll carry a thermos of
cold water for a few days, and try it.

And, I realize that I may have to replace the MC.

But, grasping at straws, I would like to "shorten the plunger depth on the
MC" as suggested by Bernard Litteau on July 15, 2002. Not really certain
how to do that, Bernard. Sounds like I should learn.

First, which part in the diagram (Bentley, 86-88 5k, diagram 47.2) is the
plunger? No such name on diagram. From flat on my back under the steering
wheel, looking up toward where the brake and clutch pivots are located,
there is an un-named ROD about the diameter of a pencil that goes into the
brake servo, through a boot, with a clevis and adjustment thread visible on
the brake pedal side of the rod.  Is that the plunger? Probably is. Looks
like I could loosen the lock nut and use vicegrips to turn the rod
(plunger?) and run it farther into the clevis. That is probably how I would
"shorten the plunger."  Next question, how many turns? And what are the
consequences of turning it too far? I am guessing at two turns. And if I
shorten it too much,  will I be able to fully apply the brakes? Will the
plunger hit something and mess up the seals inside the servo? Or, will
nothing bad happen? Brake system neophytes such as myself want to know
these things before we die.

I just need a little reassurance, probably. But I have an enormous amount
of respect for these brakes and what they do, and I don't want to
compromise that effect, or put it at risk.

I should add that for the past two years I have been running with the ABS
disconnected at the electrical plug under the rear seat. Corroded signal
teeth in the CV joints demanded the disconnect, and I just never got around
to replacing the joints. If the disconnected ABS has anything to do with my
brakes binding, let me know please. There is a hose between the MC and the
brake pressure accumulator, named "the pressure relief line." I'm guessing
that my brake binding problem _might_ be associated with that line not
relieving pressure in the MC, so I am asking about it/mentioning it.

Most of the time during this brake binding event (which lasted about 2
hours in stop-and-go on the blocked turnpike), there were no dash warning
lights showing, but at one point, after a period of the car sitting with
the engine off, the triangular red light marked BRAKE came on and stayed on
when I started the car. It eventually went off....maybe 10 minutes later.
The accumulator is a rebuilt by Southerlin.

So, let's hear from the half dozen or so that have already BTDT and lived
to teach the rest of us.

Doyt Echelberger
87 5ktq at 300k miles, in Ohio   USA