MC Master Cylinder heat causing brakes to apply.

[Doyt W. Echelberger]

Hello Scott.....I've been dealing with the same condition in my 87 5ktq,
exactly as you describe. It is the original MC, about 16 years old. From
the cabin, I tried shortening the stroke on the adjustable brake pedal rod,
without success. I tried constructing a heat shield around the MC, and the
shield prolonged the time that I could drive without "unintended
deceleration" (brakes dragging.) Gave me an extra 30 minutes, for a total
of about an hour and a half. It wasn't enough. Tried drenching the MC with
a quart of water that I carried in the trunk. Immediate relief from the
dragging condition, but temporary, lasting only about 15 minutes. But doing
this repeatedly would avoid a tow truck and get you home, eventually. Maybe
wrapping the MC with a wet towel would work even better. Didn't try it.

Having tried all the suggested remedies, I had the MC replaced today.
Didn't elect a rebuilt one. Put in a new MC. Rather costly.

Four other listers had advised me that replacing the MC was the only thing
necessary or even worth doing. All the other remedies just delay or
mitigate the lock-up long enough to get your car to a place that will
replace the MC.

I wasn't going to write this post until I had tested the new MC in the kind
of driving conditions that you describe. But that will be this weekend, and
you want answers today. So, that's my story. I am confident that a new MC
was the only thing left for me to do, since I tried all the tricks and they
didn't work. They just delayed getting to the solution by about a week. But
I haven't tested that hypothesis yet.

If you don't hear from me by Monday, you will know that I have solved my
unintended deceleration by replacing the MC.

Doyt Echelberger
87 5ktq in Ohio  USA


 >>>>>>>>>>>>>>>>>>
At 10:24 PM 6/27/2003 -0400, you wrote:

>Hey gang:
>Today's episode. '91 200 20V Sedan.
>I read about it this month and now I've felt it first hand on the central
>artery in Boston.
>Temp gauge said 97 and the car inched forward in traffic, but I didn't need
>the brakes to stop.
>The car would lurch to a stop like the brakes were firmly applied.
>The car struggled in 1st gear at idle to move.  The engine "lugged"
>Then it went away only to come back several 100 feet later.
>The ambient temps in the tunnel went to 107. (FYI: coolant temp stayed at
>half mark w/fan running)
>Wow, this is Boston and we had the windows down as the
>glass green house made more heat than the AC could cool.
>
>So I pulled the trigger and abandoned the "stop and go" commute to the Cape
>because of the dragging brakes.
>I parked in our parking garage and let the vehicle cool.
>Now down to 79 degrees.
>With-in twenty minutes I could rock the car in neutral, where earlier it
>wouldn't budge.
>Quite an experience.
>Any ideas on how to combat this?  Home made heat shield?
>Brake flush with higher temp fluid?  Drive in the winter?
>or am I looking to replace the MC?
>TIA -Scott in BOSTON