[VAC] Re: Installing a trans temp gauge

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Jim,
 In my somewhat limited experience (only about 15,000 miles of towing
with the trans temp guage), I can tell you this:

My reasons for installing the gauge in the pan were that it was easy for
me, requiring only a $2.00 fitting from the h/w store, and I figure that
the oil in the pan is what the transmission is going to "see" next. It's
about the same as the oil returning from the cooler and is obviously
cooler than the oil exiting the tranny.

The oil stays quite cool, about 140 degrees on my gauge, during normal
towing. When I hit a hill that causes a slowdown while in OD, I force a
downshift to 3rd (direct) gear. By doing this, instead of letting the
transmission do its own thing, the TCC (torque converter clutch)  will
lock up after the downshift. Remember that nearly all the heat in your
transmission is generated by the torque converter, not the gears, so it
only really heats up when the TCC is unlocked.

There's 2 situations when your tranny will heat quickly: during
campground manuevering, especially if the ground is soft or you are
moving up a hill, and during climbs or descents of steep hills with the
TCC unlocked. I've seen my gauge jump to 170 degrees in just a minute or
2 of manuevering. I've only been on one hill so far that caused the
gauge to climb even close to that.

That's why transmission shops love it when it snows: "rocking" your
vehicle heats the tranny in a big hurry!

Having a gauge in your transmission allows you to take action BEFORE
your tranny is overheated; you can downshift or pull to the side to
allow it to cool. Note that you should probably have your selector in
"Neutral", not "Park" if you stop for cooling, as many designs don't
circulate oil through the cooler when it's in "Park". If you do overheat
your oil, you can change it at your earliest opportunity, perhaps before
your transmission is destroyed by lack of proper lubrication. I've seen
a chart someplace that shows how long transmission fluid is "good" for,
depending on how hot it's gotten, and it's pretty short if temperatures
have reached 250 degrees.

Regarding your truck: if it's a half-ton (IE: "1500 series"), it has the
THM 700 R4 transmission; I think it's also known as the 4L60. While
there are no basic differences between those installed behind different
engines, the torque converter might be different and there will be
several subtle internal differences in the valve body, governor, etc.
That transmission is used in nearly all GM RWD vehicles, from mini-van
to Corvette, and there will be perhaps 30 or more variations in any
given model year. The only external difference is the bellhousing; it's
"small" for the 4-cylinder engines, "large" for the V6s and V8s. You
cannot simply swap out your tranny for another that's meant for a
different application, even if it bolts right up.

Do check your owner's manual on shifting recommendations: At least until
very recently, it was mandated to NEVER tow in OD, always shift it to
"direct". Failure to heed this advice will get very costly, and you'll
have no early warning.

It would probably be cheaper to change the axle ratio than to add a US
Gear, et. al, over/under unit, and that should be all you need,
especially with a gas engine. This will give you better performance,
maybe better mileage, and will be easier on your tranny.

                                                    <<Jim>>