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Discussion Starter · #1 ·
Hi Fellas, My buddy is working on an '04 avalanche and ran into a trans problem the other day. It will upshift from first to second fine but not out of second after about 35 mph. In fact when he steps on the gas in second it sounds like its trying to up shift but the engine just revs and you can see the tach needle just swing left and right.when he lets off it locks back into 2nd and will lunge forward 'till about 30-35 mph. and then do the slipping thing.

Any ideas?
 

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Wow first and second and I guess reverse works. This is classic 3/4 clutch is gone. Pretty common.

More detail as to mileage and how this vehicle is used. These tranny’s really need beefier parts and a damn good external cooler.

My own build is a 700R4 that replaces a 4L60E. Nothing but the case is GM, I run ATI Super F, Synthetic, 20 wt, type F. I think Ford named this stuff type F ‘cause when it shifts you effing know it. My wife hates how it shifts so she doesn’t even like riding in it let alone ask to use it. Of course when I took the electronics out of it I structured the electrical system like that of an AT-6, so if you don’t understand how to start an old airplane radial motor you ain’t even going to get this outta the garage.

Bogie
 

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Discussion Starter · #5 ·
Thanks Guys.
"Wow first and second and I guess reverse works. This is classic 3/4 clutch is gone. Pretty common.

More detail as to mileage and how this vehicle is used"

Yep reverse works just fine. The truck has over 100K on it. It's a daily driver that gets rest now and then when he takes his other car.
 

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I don't even change transmission fluid every 25k. 40k if used hard or 60k normally or every 10 years if it sits alot(moisture/gaskets). Filter and gaskets at the same time.
 

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Thats because they are a th350 with a extra gear added in a 5500lb truck that the curb weight alone strains them.

You slap another 1500 to 2000lbs on the back then run 75 in overdrive thats going to shorten the life.

It should have never went into a truck or behind a v8. Great for a car or maybe a 4200 envoy that never tows. But not a 1/2 ton.

Good news is they are everywhere. I get rid of them for between $100 to $150. I try to take a test drive. But the trans (or brakes/frame) is usually the reason I bought the truck.
 

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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
 

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What GM needs to do is put the Allison behind these 1/2 ton trucks or at least make it an option if you plan to tow with it. Then these trucks would be bullet proof. An LS backed with an Allison, oh boy!

Keith
 

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What GM needs to do is put the Allison behind these 1/2 ton trucks or at least make it an option if you plan to tow with it. Then these trucks would be bullet proof. An LS backed with an Allison, oh boy!

Keith
8.1.
It gets around 8mpg when towing over hills.
Most people either stick with the 6.0 or jump over the 8.1 to the diesel.

Going from 60 to 80 or even 85 is a easier swap and will still give mileage in the teens towing.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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I'm sure it has towed something in its life and I highly doubt the fluid has been changed every 25K
Is the plan to get a used transmission or is your buddy getting it rebuilt? Either way, the great information here on cooling and fluid changes are a must.

Let us know if your buddy is going to talk to a rebuilder. There are a few upgrades worth incorporating into the rebuild. We can provide some ideas and some rationale for doing so, if you're interested.
 
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