PT36 retarder & other things

[Don Bradner]

The difficulty is in determining the effect of short-term retarder temps
compared to elevated "operating" temps.

Allison says "Normal range 160-200, Maximum 330 Intermittent"

The 330 number for my HT755 is found here:
http://www.allisontransmission.com/servl...bs&Fi\
leToGet=OM1475EN.pdf and I imagine I can find a similar listing for other
Allsons (give me a model number).

On 8/23/2007 at 3:19 AM davidkerryedwards wrote:

>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
>> >
>> >
>>
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