700R4 towing

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Supercharged111

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in 3rd, TC unlocked you are generating more heat because the TC is slipping, but i believe you have full flow through the cooler. As long as you have an adequate cooker you should be OK. The main issue is being in 4th/OD unlocked as converter flow is restricted and there is a lack of lube to the geartrain. this is where you will run into problems.

Can you expand more on why converter (or any) flow is restricted in 4th vs any other gear?
 

studigggs

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38K miles on the GM built 4L60E behind my stock L31. Broke the case even when it failed. 40K on the replacement 4L65E that was built up to hold 450+ hp and it broke hard parts. They are that bad. I have thrown whatever I want at a 4L85E I swapped in that had 110K miles in a fleet-maintained van that was totaled.

If you are breaking transmissions every 40k miles, its probably not the transmission's fault. If your situation was anywhere near normal GM wouldn't have used the same trans for the last 30+ years in light duty trucks. They'd be bankrupt. Original 4L60 w/180k on mine, daily use and I keep it loaded as the book states. Shifts like butter and the fluid is cherry red when I drop it every 30k. I gotta find some wood to knock on.
 

HotWheelsBurban

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One of my old friends who used to build transmissions, told me the earlier '60s are the weakest ones. By the late 90s they're lots better. Of course an '80 is the best, but they'll eventually break if you whale on them enough....
 

HotWheelsBurban

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If you are breaking transmissions every 40k miles, its probably not the transmission's fault. If your situation was anywhere near normal GM wouldn't have used the same trans for the last 30+ years in light duty trucks. They'd be bankrupt. Original 4L60 w/180k on mine, daily use and I keep it loaded as the book states. Shifts like butter and the fluid is cherry red when I drop it every 30k. I gotta find some wood to knock on.
You do maintenance on it like GM dreamed everyone would/should!
 

L31MaxExpress

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If you are breaking transmissions every 40k miles, its probably not the transmission's fault. If your situation was anywhere near normal GM wouldn't have used the same trans for the last 30+ years in light duty trucks. They'd be bankrupt. Original 4L60 w/180k on mine, daily use and I keep it loaded as the book states. Shifts like butter and the fluid is cherry red when I drop it every 30k. I gotta find some wood to knock on.
It absolutely was the transmissions fault. Considering my 97 belonged to my parents to start with and neither of them had a lead foot. The first 4L60E destroyed itself on a 1-2 shift taking off at moderate throttle with my mom driving the thing. The 4L65E blew up on a 4-2 downshift getting on the highway while I was driving it after I owned it. Had shorty headers and a mild cam making about 350 hp at the crank. 4L60E derived garbage should have never gone into the vans as GM themselves even lacked the trust to put a 4L60E behind a 4.3L 8-lug and used the 4.3/4L80E in many of them. 4L60E definitely should not have come with a 3.42 gear behind it in a van with the L31. Loads of stress on that POS transmission just getting the thing rolling from a stop. The Astro/Safari vans with the 4L60E also had a habit of nuking the 4L60Es at low mileage. I put a couple dozen 4L60Es in the M vans when they were newer and they all had under 100K on them. The 4L60E is like an undersized fuse in the driveline.
 
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Schurkey

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Isn't there some issue, perhaps a BIG issue, with the cooling circuit on the 700R4 when the TCC is unlocked, e.g, as might be likely when towing (esp. in 4th)?
That's exactly what my favored trans shop told me the first time I popped the '700 in my '88 K1500.

And I thought "Naw, GM wouldn't be that stupid..."

But twice I've wiped out the trans in that truck, and both times the planetaries have been destroyed--broken teeth, no rollers left in the planet gears. (and more issues in the friction material--bands and clutches) but the total failure of the planetaries has me convinced that they're suffering from lack of lube even if they're not really discolored from heat.
 

Supercharged111

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That's exactly what my favored trans shop told me the first time I popped the '700 in my '88 K1500.

And I thought "Naw, GM wouldn't be that stupid..."

But twice I've wiped out the trans in that truck, and both times the planetaries have been destroyed--broken teeth, no rollers left in the planet gears. (and more issues in the friction material--bands and clutches) but the total failure of the planetaries has me convinced that they're suffering from lack of lube even if they're not really discolored from heat.

That being said, you don't seem like the type to cruise around everywhere in 4th unlocked.
 

Erik the Awful

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I wonder if the issues are parts quality/cheapskate problems more than design problems. Some trannys nuking at 40k and others lasting 300k direct me to think more towards inconsistent part quality.

I do think GM tried to design the 4L60 to be "just strong enough", but that only works if you have strict quality control. Toss in a few accountants badgering part suppliers for another nickel's savings off each bit and suddenly the 4L60 becomes a disaster.
 

tayto

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unlocked the TC will generate more heat (fluid coupling). when its locked up it is now physically connected, so less heat will be generated. let's not forget the th350 and th400 ran without lockup FOR YEARS with no issues. I will have to check the hydraulic diagrams i am in the middle of a house move and don't have access to this stuff at the moment.
 

Supercharged111

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unlocked the TC will generate more heat (fluid coupling). when its locked up it is now physically connected, so less heat will be generated. let's not forget the th350 and th400 ran without lockup FOR YEARS with no issues. I will have to check the hydraulic diagrams i am in the middle of a house move and don't have access to this stuff at the moment.

Nobody's questioning locked running cooler than unlocked. Both my trucks have trans temp gauges, you can see that for yourself. I'm curious to hear what you have to say with the diagrams. That said, there is a bunch of info here.

 
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