700R4 towing

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1998_K1500_Sub

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...there is a bunch of info here.


This link (below) shows two hydraulic circuit diagrams of the TCC (locked and unlocked) with detail that I didn't see in @Supercharged111's link:


All I've managed to glean from the two figures is that:

- when unlocked, the valve routes all of the fluid to the TCC; from the TCC the fluid then returns to the valve where it is then routed to the cooler circuit (and then on to the "lube" circuit that lubricates the front of the transmission), and

- when locked, the valve splits the fluid; part of the fluid from the valve (a) is routed to the TCC, and from the TCC the fluid returns and is exhausted to the pan and (b) the remaining part the fluid from the valve goes to the cooler circiut.

The volume of fluid passing through these components in the unlocked and locked states isn't clear to me. I haven't determined what device / orifice is controlling the fluid volume in the locked or unlocked case.

Volume of fluid is key, with higher volume offering improved (a) heat transfer to the cooler and (b) oil flow to the "lube" circuit.

My observations are NOT definitive. Maybe someone can springboard from my comments.
 

L31MaxExpress

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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.

It has been close to 20 years ago now, but when I was in my Automatic trans class at the trade school I attended we built 4L60Es. There were like 20 of us in the class and we built like 5 units in groups of 4. If I remember correctly the problem is actually more low line pressure causing lack of cooler flow. If the bushings, lip seals, etc are worn and have fluid leak, the converter charge and thus cooler flow are limited. A 700r4 and 4L60E do not have much in the way of excess pump flow especially at lower rpm. When we had them hooked up to gauges on the transmission dyno the the cooler line pressure was extremely low even on units that had been gone through while they were at low rpm. When you shifted it from say Park to Drive the cooler line pressure was non existent during the shifts. One of the units had Zero cooler line preasure and low line pressure. Subsequent tear down on that unit found that a teflon sealing ring had been pinched during assembly. It still shifted through the gears but would not apply lockup and would have failed in a short time in a vehicle. That team had to go back through that transmission, find and correct the issue before they had a passing grade for that transmission build.

Similarly the AOD that I had a hand in building would not shift. On the dyno we noticed it did not have any governor pressure to the governor pressure tap. We removed the tail housing, swapped the governor and then it shifted fine. When we pulled the old governor apart it had rusted stuck valving inside. Sticking governors were a problem on the old AODs.
 
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Supercharged111

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It has been close to 20 years ago now, but when I was in my Automatic trans class at the trade school I attended we built 4L60Es. There were like 20 of us in the class and we built like 5 units in groups of 4. If I remember correctly the problem is actually more low line pressure causing lack of cooler flow. If the bushings, lip seals, etc are worn and have fluid leak, the converter charge and thus cooler flow are limited. A 700r4 and 4L60E do not have much in the way of excess pump flow especially at lower rpm. When we had them hooked up to gauges on the transmission dyno the the cooler line pressure was extremely low even on units that had been gone through while they were at low rpm. When you shifted it from say Park to Drive the cooler line pressure was non existent during the shifts. One of the units had Zero cooler line preasure and low line pressure. Subsequent tear down on that unit found that a teflon sealing ring had been pinched during assembly. It still shifted through the gears but would not apply lockup and would have failed in a short time in a vehicle. That team had to go back through that transmission, find and correct the issue before they had a passing grade for that transmission build.

Similarly the AOD that I had a hand in building would not shift. On the dyno we noticed it did not have any governor pressure to the governor pressure tap. We removed the tail housing, swapped the governor and then it shifted fine. When we pulled the old governor apart it had rusted stuck valving inside. Sticking governors were a problem on the old AODs.

So. . . does locking the converter reduce the transmission's demand for fluid flow vs unlocked?
 

Supercharged111

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It does not really alter the demand much, however it does greatly reduce the cooling demand. Less BTUs of heat because of the reduced slippage.

I knew about reduced cooling demand, wasn't sure if what you were saying was going to line up with the bit about unlocked converters sending less fluid through the cooling circuit.
 

Erik the Awful

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It has been close to 20 years ago now, but when I was in my Automatic trans class at the trade school I attended we built 4L60Es. There were like 20 of us in the class and we built like 5 units in groups of 4.
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We built 700R4s individually, and if it didn't run right on the dyno you had to tear back into it and fix the problem. One person in our class of 12 had their transmission work correctly on the first try. I was meticulous, and then forgot to hook up the shift linkage inside the case. Doh!
 

1998_K1500_Sub

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There’s a GM sticker on the driver’s door of my father’s former 1995 K1500 5.7 4L60E 3.73 that specifically instructed to not tow in OD.

I assume the 1996 and later powertrain control was more advanced and mitigated “the problem”… at least GM did NOT put that same “do not tow” sticker on the door of my ‘98 K1500 L31 4L60E 3.42 Suburban as was on Dad’s ‘95.

I took a picture of the sticker on the door of Dad's 1995 5.7L TBI K1500, it says...

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Supercharged111

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I took a picture of the sticker on the door of Dad's 1995 5.7L TBI K1500, it says...

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What it should say is "sorry, we fvck3d up and put a POS transmission in this thing so you can't do anything in OD"

I believe 3500# and under, the manual says you can tow in OD in my 98, but I'd have to get off my lazy ass to verify.
 

1998_K1500_Sub

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I believe 3500# and under, the manual says you can tow in OD in my 98, but I'd have to get off my lazy ass to verify.

I suspect the powertrain control improved in 96 and later years; perhaps other "improvements" were made then too, to mitigate whatever problem(s) this sticker was intended to address.

Just a guess.

My '98 K1500 Sub doesn't have that door sticker.
 
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