PT36 retarder & other things

[davidkerryedwards]

I found this on another website:

Why Atf Wears Out
An automatic transmission creates a lot of internal heat through friction: the
friction of the
fluid churning inside the torque converter, friction created when the clutch
plates engage,
and the normal friction created by gears and bearings carrying their loads.

It doesn't take long for the automatic transmission fluid (ATF) to heat up once
the vehicle
is in motion. Normal driving will raise fluid temperatures to 175 degrees F.,
which is the
usual temperature range at which most fluids are designed to operate. If fluid
temperatures can be held to 175 degrees F., ATF will last almost indefinitely --
say up to
100,000 miles. But if the fluid temperature goes much higher, the life of the
fluid begins
to plummet. The problem is even normal driving can push fluid temperatures well
beyond
safe limits. And once that happens, the trouble begins.

At elevated operating temperatures, ATF oxidizes, turns brown and takes on a
smell like
burnt toast. As heat destroys the fluid's lubricating qualities and friction
characteristics,
varnish begins to form on internal parts (such as the valve body) which
interferes with the
operation of the transmission. If the temperature gets above 250 degrees F.,
rubber seals
begin to harden, which leads to leaks and pressure losses. At higher
temperatures the
transmission begins to slip, which only aggravates overheating even more.
Eventually the
clutches burn out and the transmission calls it quits. The only way to repair
the damage
now is with an overhaul -- a job which can easily run upwards of $1500 on a late
model
front-wheel drive car or minivan.

As a rule of thumb, every 20 degree increase in operating temperature above 175
degrees
F. cuts the life of the fluid in half!

At 195 degrees F., for instance, fluid life is reduced to 50,000 miles. At 220
degrees,
which is commonly encountered in many transmissions, the fluid is only good for
about
25,000 miles. At 240 degrees F., the fluid won't go much over 10,000 miles. Add
another
20 degrees, and life expectancy drops to 5,000 miles. Go to 295 or 300 degrees
F., and
1,000 to 1,500 miles is about all you'll get before the transmission burns up.


Kerry
82 FC 35
Denver


--- In WanderlodgeForum@yahoogroups.com, "davidkerryedwards"
wrote:
>
> Those temperatures seem really high to me. I was looking at hose temperature
ratings
> and fluid temperature ratings when I was redoing my power steering. My
recollection is
> that standard hydraulic hose was rated to 250 degrees and the expensive high
> temperature hose was rated to 325 or 350. I think regular transmission fluid
was rated
as
> functional up to about 250 degrees and synthetics up to about 350. These
numbers are
> from my memory, If anyone else has knowledge about the functional temperatures
of
> transmission fluid, I'd like to know. I'd be quite concerned with
temperatures over 300
> degrees.
>
> Kerry
> 82 FC 35
> Denver
>
> be sure to keep it below
> > 320-330 degrees or you'll shorten the life of the tranny fluid
> > greatly. Most commercial bus drivers have to change the tranny fluid
> > every 50K miles when using the tranny retarder often. Mine easily goes
> > from 230 to 300 degrees when descending a steep off-ramp. One way to
> > slow the heat is to engage the fan override and let the hydro fan rob
> > 25-30 horses from the engine and cool the tranny fluid a little
> > quicker. On an off-ramp it does not make much difference, but on the 3
> > or 4 mile grade, you can usually make it to the bottom under 320
> > degrees if you also use the service brakes along with the tranny brake
> > and fan to slow the coach down.
> > Shane Fedeli
> > 85PT40
> > Hershey, PA
> >
> >
>