Re: brakes and lonnnng downhills

[pjrose@servtech.com (Phil & Judy Rose)]

Dan Simoes spake thus:
>> >> Anyway, my question concerns braking during the return trip, which as some
>> >> of you know, is a 7-mile long drop from 6000 feet--all done at about 20-25
>> >> mph with brakes working nearly full time.
>> >
>> >That's a good way to get killed.  You're supposed to descend the
>> >mountain in low gear, touching the brakes when needed...
>>
>> _What's_ a "good way to get killed", Dan?
>
>Chill, I'm not picking on you.

Well, just somewhat insulting; same effect.

>You say above:
>*** with brakes working nearly full time ***
>
>*That's* a good way to get killed.  I stand by my statement.

I'd say you're standing on thin ice, next to a statement you make without
learning exactly what my particular "way" (good or not) actually was.
>
>> Of course I was in low gear and
>> using the brakes just when needed.
>
>Then that's a different story, isn't it?

No. Just some elaboration needed since you unexpectedly had chosen to
*assume* I didn't have the sense to use a low gear. Oh, I guess I'd better
mention the engine _was_ running?  Anyway, "nearly full time" doesn't (in
my version of the English language) mean the same as "full time" or
"constant". I admit it's an ambiguous phrase--mainly because I can't be
very specific about the amount of braking. It was great gobs o' brakin'
(how's that?)--relative to normal-grade driving.

More to the point: I applied the brakes for several seconds every 200 or so
feet, which is a lot of braking for 7 miles (150-200 pedal applications?)
In normal driving, brakes are used for probably 1 to 5% of the time (even
less?), so when my foot is pressing the brake for what seems 50% of the
time, that qualified as _nearly_ full time as far as I'm concerned. Maybe
you thought I was braking hard for 95% of the time?  But what justifies
_that_ conclusion? You're entitled to the opinion that even 50% was
excessive, but all I can say is that was about what I needed to maintain a
low speed.

I also don't believe I said or even implied anything one way or the other
about amount of pedal pressure used or needed. Nothing about fading,
smoking, glowing, glazing, melting, warping, erupting...

>
>> Maybe you've not descended Mt. Washington in 2+ tons of Audi.
>
>Yes, as a matter of fact, I have, in both my 4kq, my CQ, and on my
>K75s motorcycle, all at a pretty good clip (ask Jim Griffin :) ).
>Two years ago I literally had to cut off a moron
>in an Escort who was riding his brakes all the way down the hill,
>all 4 wheels smoking like hell, totally oblivious to what was
>happening.

I don't doubt for an instant what you did or witnessed while descending the
mountain, but it has little to do with my fully-loaded '91 200q (4700 lbs?)
with converted front brakes.  And since you managed to ride down at a
"pretty good clip"--a good way to get killed, BTW :) --it has even less
relevance to my 20 mph trudge.

>> And I stated
>> that the brakes never heated enough to cause significant fade.
>
>Like I said, ride the brakes all the way down and you won't make it
>there.  There's a good reason why the hillclimb is run UPHILL
>and not downhill, namely, no brakes can hold up to that kind of
>treatment.

Is there gonna' be a _test_ on this material? :)

Why the need to lecture about what happens when the brakes are "ridden all
the way down"? Like *I* said, I didn't do that. Brakes _weren't_ smoking
and they didn't even fade noticeably. Heck, if the brakes were ridden as
hard as you seem to assume, it would have been durn near impossible to
*feel* the wheels and judge one end cooler than the other. Duh, let's see,
uh, my hands have only 2nd degree burns from the fronts but (damn!) there
are 3rd degree burns from the rears.  :(

So, now I'm chilled, and back to my question: why were the rear brakes
hotter than the fronts?

>> Is there any adjustment available in the
>> proportioning valve for this car?
>
>Yes there is.  It's a common cause for UFO brake gripe.  My mechanic
>Greg maintains that a properly setup UFO car will outbrake a regular
>setup and last just as long.

I have the G60 conversion (by Audi). I don't know if the conversion
procedure specifies any change in the proportioning valve or its setting.
Or, as you imply, it's possible that the setup may have been wrong from the
beginning (i.e., pre-conversion).


Phil

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