I think the big problems with the 700R4/4L60 and the 4L60E family that grew out of them when used in trucks the loading is too high especially in 4th which as with all overdrives places all the components within the transmission at a significant disadvantage in load transfer, this is seen as heat. The theory is to load the engine higher for the given RPM this results in higher thermal efficiency on the engine. To a big extent this was extensively used in aviation with the big engines run in cruise lean mixtures with the RPM’s kept low but the prop taking big bites of air. Back in the day this was carefully monitored by the flight engineer keeping very close eye on mixture ratio and head temps to guard against overheating and detonation.
The problem especially in trucks is Detroit automates this function using generalities that don’t necessarily apply well to a road vehicle that sees stop and go, variable speeds, and variable loading based of topography. Detroit has been stuck forever in designing vehicles that are engineered for cruising on a near flat interstate at a bit over the posted limit on an average weather day. Your real world experience may be different.
Then we collide with Detroit cost cutting a place where this shows is years ago if you bought anything rated higher than half ton in 2 wheel drive they beefed up the cooling system. Now and for 20 to 30 years or so the beefed up cooling system is an extra cost option that most people pass on in favor of useful things like a throbbing stereo and power windows.
I have a friend that lives in this trap, many years ago he bought a GMC half ton, stretched cab with a 350 and 4L60E. It ran fine for a couple, three years. Then he loads up to take the family camping and boating at Sun Lakes on the desert side of the mountains. But they never get there the truck with a camper stuffed with supplies and gear, the boat on a trailer behind the tranny goes up in smoke in rush hour traffic on a hot day in downtown Seattle. When I next saw him my question was did you opt for the cooling option, answer no they aren’t needed. So when he gets it fixed he trades “that piece of junk” GMC on a Dodge pickup, same thing half ton, crew cab. He does not option up the cooling package. A couple summers later it’s tranny goes up in smoke but at least this time he got to the middle of nowhere out in the desert when that let go. Then he bought a Nissan Titan, that automatic fried itself on a trip to Texas just after it got out of warranty. It was replaced with a junk yard transmission by an independent shop, but since it has an ID code different from the truck’s the computer won’t shift it. So it had to be transported to a big city Nissan Dealer who charged a princely sum to reprogram the tranny’s ID so the truck’s immune system would recognize it as a friendly part.
The takeaway message in my mind is everybody is running on the cost cutting edge they are designing to an average which if you stay at that point or below your probably OK. If you’re running above that point not so much. Basically the pickup truck has been redefined and redesigned as the replacement for the American sedan unless you belly up to the bar to order what today are the heavy duty option package which was standard fare years ago when pickups were vehicles that were expected to earn their keep on ranch and farm or in the trades. Today the standard package just isn’t up to the needs of doing hard work, they’ve become family transportation.
So responsibility for design to loading is now the buyer’s responsibility. Hopefully, the average purchaser knows as much about automotive engineering as they do about their music preferences.
And my wife wonders why she can’t pry my hot rod 89, S15 out of my grasp?
Bogie
