700R4 towing

[Supercharged111]

Not according to that one ****** over on trailvoy, swears up and down towing with an unlocked converter won't hurt a thing. @Schurkey knows who I'm talking about. Negated cooler flow never came up, but I am curious to hear more about this.

 

[L31MaxExpress]

You think they're weak now? They used to be so fragile/brittle as to be totally unusable. The early TH 700-R4s used to pop when used behind 2.8L V-6s in S10s and Camaros. Grandma drivers would fail them in Caprice Classics with 4.3 V-6s. The TH350 was considered a "heavy-duty" trans in '84 when I was in a Chevy dealership. Numerous companies sold crossmembers and "conversion kits" to remove a '700 and stuff in a TH350.

By '88, they'd made about a hundred upgrades, many of them "major" to the silly thing. It was ALMOST a transmission by then. But not one suitable for a full-size truck.

Which is weird. The ONLY one I have had hold up at all was a 10/1982 built unit. Nearly 300K on it dragging around the 83 G20. My parents had that van from 1983 until I got it as a hand me down and started driving it in 2002 at 180K. I put a cam in the 305 and head work on it around 200K. Put another 50K on that transmission with a 305 making about 300 hp. Then put a 400HP 350 in front of the 250K mile trans. The transmission held together until about 300K, then finally let go. That van had a trailer behind it for many miles and I can say for certain my parents never took it out of D which was overdrive on the old 1983 shift indicator that was D-3-2-1 marked. A local transmission shop that was well known for building performance 700r4s built a 1992 700r4 core for it. The newer "4L60" was an absolute garbage transmission for the early application. Shift points were off compared to the stock unit, the nice firm 1-2 shift was gone with the upgraded auxiliary valve body as well as the 2nd and 3rd gear lockup. The newer TBI valve body calibration was not a good match for the carbureted small block.

 

[Komet]

Assuming it's a 700R4 from 1992, it's good to tow whatever the truck is. What's going to kill it is heat, so your best bet is to install a trans temp gauge and an additional trans cooler with thermostatic bypass (controversial opinion: in series after the factory rad cooler). Personally I'd leave it in D and pull over to let it cool down if you're still seeing temps climb.

 

[studigggs]

I dont think the 4l60/700R4 is that bad. Heck, nearly every sketchy landscaper in Southern California drives 12 hours a day in stop-and-go lugging around a twin axle dump trailer full of gear and plant carcasses. Their clapped out GMT400 keeps on going. Rarely do I see 90's Ford's or Dodges being used as such.

 

[L31MaxExpress]

I dont think the 4l60/700R4 is that bad. Heck, nearly every sketchy landscaper in Southern California drives 12 hours a day in stop-and-go lugging around a twin axle dump trailer full of gear and plant carcasses. Their clapped out GMT400 keeps on going. Rarely do I see 90's Ford's or Dodges being used as such.

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.

 

[1998_K1500_Sub]

Not according to that one ****** over on trailvoy, swears up and down towing with an unlocked converter won't hurt a thing. @Schurkey knows who I'm talking about. Negated cooler flow never came up, but I am curious to hear more about this.

I'm digging around trying to find a credible reference for my remark about "TCC unlocked" vs. flow through the coolant circuit. I posted about this earlier in this thread.

Here's perhaps the most credible post on that subject I've found (so far):

Towing in 3rd or drive​

https://bobistheoilguy.com/forums/threads/towing-in-3rd-or-drive.245366/page-2

I can't decide yet if this Sonnax story has any bearing on the subject:

Anatomy of a Transmission: Oil Flow in the Pump-PR-Converter-Cooler Lube Circuits

View Transmission Parts for Resolving & Preventing Torque Converter ProblemsRemember the old nursery rhyme, “The hip bone’s connected to the thigh bone, the

www.sonnax.com

Searching Google for "700r4 cooler flow TCC unlocked" yields links to various forums.

I wonder if @tayto can comment on this topic . I've seen some good comments in his posts.

 

[tayto]

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.

 

[92GMCK2500]

Question is, is the factory trans cooler adequate? Mine runs through the rad (34x17" size) then aux cooler.

I lug the camper around in 3rd always. At 100 km/hr it sits around 2800 rpms, which is peak torque for the L05 350. I have 4.10 rear and stock tire.

In OD (4th), it hunts gears, 4-3-4 constantly which is worse case scenario for your trans.

 

[GoToGuy]

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.

" More heat " well driving home from work this summer it was 113° F. I'm sure it generated more heat. Then did it generate more heat driving my wife around Christmas shopping in third on a 36° F day. That's vague terminology, implying a problem. Is it within operating parameters or not? What is " torque converter slipping"? Normal TC operation? Are you calling the propulsion, velocity loss between rotor and stator " slipping"? " In 4th/OD unlocked " (?) . What is your reference I'd like to read it.
It's a no brainer, the " Owners Handbook" ( the glove box edition nobody bothers to read). Clearly states tow capacity and Gross Combined weights. Combined means truck and trailer.
And states to tow in third or drive not fourth or OD. Sure something's are engineered better than others, Cosworth Vega, Ford Pinto, 69 Z28, 87 Buick GNX. I'm not gonna try to pretend I'm smarter than GM engineers. Everybody's got a this happened to me. I follow the handbook first. Your choice.
Good luck.

 

[1998_K1500_Sub]

It's a no brainer, the "Owners Handbook" … states to tow in third or drive not fourth or OD. I follow the handbook first. Your choice.
Good luck.

In support of this ^^^…

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 know the current owner of Dad’s truck and can get a picture of the sticker upon request.

I assume the 1996 and later powertrain control was more advanced and mitigated “the problem”… at least GM didn’t 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.

We can debate “the problem”… and it’s worthy of debate:

- lubrication insufficiency when TCC unlocked?

- heat due to slippage and/or reduced flow to cooler (perhaps in combination) leading to excessive (>230F?) oil temps?

- enhanced “holding” when operating in driver-selected 3rd, on account of engagement of the overrun clutch assisting other clutches (see markup in attached image)?

- other?

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