Towing with a 4l60e, best practices.

I usually would drop into OD when going downhill to make life a little easier on the engine.

But yes, key is not to load too much in OD, and shift manually at light throttle so the trans doesn't kick down by itself at heavy throttle.  Shifts are when the majority of wear happens, especially on drive by cable vehicles that can't cut engine power during a shift.

Knurled. said:

especially on drive by cable vehicles that can't cut engine power during a shift.

A lot of modern-ish drive by cable vehicles with autos pull timing during shifts to reduce power output.  

My Suburban with an original and high milage 4l60e was fine towing. Did it across the mountains on the edge of CA - the truck struggled (maxing at 45-55 on some passes) and got hot, but I left it in 3 - and then on the downgrades dropped into overdrive. It never even hiccupped. 

Not the heaviest load, but the uhaul trailers weigh in at around 2.7k from what I remember + 1.5k for the exocet and a truck full of stuff. 

Is there a better fluid to use on the GM  trans ?

And where is the best place to put a trans fluid temp gauge ?

I killed off an overdrive GMC trans in the middle of Kansas years ago , not a fun day !

californiamilleghia said:

Is there a better fluid to use on the GM  trans ?

And where is the best place to put a trans fluid temp gauge ?

I killed off an overdrive GMC trans in the middle of Kansas years ago , not a fun day !

Good questions!

Looking forward to seeing the answer 

Any decent synthetic fluid should be fine.  Pan temp is a good indicator of when you're working it too hard.  Try to keep it under 200*, definitely don't let it past 210 - 220.  

There should be a test port on the passenger side with a 1/8" NPT plug in it.  Temp sensor can go there.  Since the whole case is aluminum, and fluid is getting sloshed everywhere rather violently, most anywhere will do the trick and get you pretty close.  Remember that the most important temps can't be read.  By the time the overall fluid reaches a bad level of heat, that means the fluid between the clutches is already toast.

You can do a synthetic ATF if you wish, but it can have mixed results.  I honestly use the cheap bulk stuff and do a filter/pan every 60k.  ATF isn't magic juice, it just needs to have the correct lubricity and viscosity.  When I ran the shop, I think we got ours delivered from Shell and it worked out to $1.04/qt and we warrantied every transmission we built for 2 years.

Right now in my garage I have a gallon of Auto Zone brand ATF and a gallon of STP ATF.

On the subject of coolers, it can't hurt to have one, but please install it before the radiator.  Cooler is not better... correct is better.  Fluid that is too cool can be just as bad as fluid that is too hot.  If you put it after the radiator, it might get super cool in the winter and not as much in the summer.  Putting it before the radiator means that it will dump the bulk of the heat first, then the radiator can be much more efficient about making it the right temperature.  In the winter that might mean your new cooler will drop the temps to 170 and the radiator will bring it back up to 200.  In the summer, that might mean the new cooler can only drop it to 220, and the radiator will have an easier time getting it down to 200.

The radiator cooler won't (can't) prevent over-cooling.  The cooler is in the cold side of the rad which might only be 80* on a really cold winter day.  So if you're worried about over-cooling, run a thermostat in the trans cooler lines.  And when you're working the engine hard and pushing the limits of the cooling system, the cold side of the rad could be at 200 - 210 which is already hotter than you'd want the fluid returning to the trans to be.  The radiator is also most effective when trying to cool the hottest fluid (right out of the converter).  

So IMO, aux cooler goes after the radiator cooler.  Or the radiator cooler can be bypassed entirely if the aux cooler is really big and then a thermostat added if very cold weather is a possibility.  

admc58 said:

NEVER unlock the torque converter in OD when towing...

Seen this comment a few times and want to circle back.

How do I know whether it's locked or unlocked? Is it just a foot thing or is there some manual way to control this?

This thread is relevant to my interests, having recently picked up a 95 C1500 with 172k on what I believe is the original 4l60e. This is the first automatic that I've owned on purpose and my knowledge is pretty basic. 

What about shift kits? Is there any functional advantage or disadvantage to firming up shifts this way versus through the computer, or are these a relic of the pre-computer days? Would firming up the shifts help to prolong the life of a tired old trans, or just kill it quicker?

Time to jump in with a question: I have a new-to me 2000 Silverado 5.3 with some large number of miles on the tranny (it is not the original one as it is nice n shiny on the bellhousing, but the last owner put >100k out of the truck's 207k miles on it). The truck has the tow package, so I can see that there is the GM tranny cooler in front of the radiator.

I will be towing a 5,000 lb trailer for a few hours every month. Does the hive think I need a need an additional cooler, or if I follow the keep-it-in-third, take it easy advice I will be ok? Thanks!

If it's already got what appears to be decent cooling, I'd just add a temp gauge and monitor it.  If it runs on the warm side when towing, add more cooling.  If it doesn't, you're good to go. 

In reply to rslifkin :

Thanks! Appreciate the sage advice.

Any reason to add a spin on filter that seems to come with a lot of the add on tranny coolers ?

In reply to californiamilleghia :

An external filter won't hurt (it's usually a finer filter than the in-pan filter on most transmissions) but it's not necessarily required.  It can help to keep the in pan filter cleaner though meaning you can just change the external filter and drain/fill the fluid without needing to drop the pan for a filter change at every fluid change.