towing with a GM 4L80E 4 speed auto

[Rot Box]

Does anyone tow with a GM 4L80E or 4L85E auto? I have a 95 K2500 6.5L- (F-code, HO) TD with a 4L80E auto and 4.10 R&P's. The truck has enough grunt to pull just about anything, but I am worried about using 4th when towing my rig to Moab this year. I have heard that these trannies are not to designed to tow in 4th, and with 4.10's and a 6.5L diesel I would be redlined at 65mph in 3rd any suggestions? I also have the largest factory trans cooler so I don't think that excessive heat will be an issue. Thanks

 

[mbryson]

I think as long as you're not 'lugging' and making it shift a lot, you should be OK in OD. It wouldn't hurt to add a tranny temp gauge and then you'd know when you're working it.

(Richmond, huh? Interesting...... Been there a time or three.)

 

[I Lean]

I'm no tranny guy, but I'm pretty sure the tranny killer is shifting into/out of OD, rather than towing in it. If it's able to hold OD while towing, I'd think you'll be fine--then just kick it into 3rd when you start climbing, or your load is heavy enough to make the trans "hunt".

 

[kirk86CJ]

I towed a lot with a 4L80. I ran it in OD when it would stay in gear. I pulled 14,000 lbs a couple times. (It had a supercharger) The biggest concern like said above is heat. The TC on these doesn't lock up until you get up to about 60 mph. If you fall below 60, you lose power, and it gets hot.

I found this on another site, and did it. This mod is awesome. I could manually lock the tc up at 35 mph. My heat issues were GONE. I changed my fluid often - and every time it got above 230.

"I found out that if the thermistor in the transmision is working correctly and it senses a temperature over 284 deg F then the trans will go into hot mode, freeze the shift adapts and record in history the code for a hot trans. It will not turn on the service engine soon light.

So what I did was to wire a switch so that a 50 Ohm resistor could be switched in and out of a parallel circuit with the transmision thermistor. What this does is trick the PCM into thinking the trans is close to 300 deg in temp so it works the TCC in hot mode. The goal is to make it think its hot without thinking that the thermistor circuit is shorted. Also I wired in an LED to the TCC solenoid so I could tell when the PCM was calling for the TCC to be locked.

Here's what happened with the switch on. The TCC will lock with the trans shift lever in second when it exceeds about 25mph. Also the TCC is used longer, more frequently and under higher throttle in 3rd and 4th. It still goes off when a shift is made. Also when slowing down the TCC will stay locked until you let almost completely off of the accelerator pedal. Shifts were still smooth.

I did see one thing though that needs to be watched out for. In some situations with a very heavy pull such as accelerating hard up a hill the TCC may continue to slip until it can catch up. What you need to do in this case is slack off the throttle until the TCC completely locks up then reapply throttle. It will then hold the big load."

 

[Tacoma]

.... and if anyone has a 4L80 they need to get rid of, say so. I am looking for one LOL

 

[Rot Box]

Hey thanks for the help! do you know of anywhere I could get instructions on how to do this mod? I think It would help me a lot. I always try to go easy on my trans and It will lug down to nothing before it shifts, but like you guys stated above when the TC unlocks it builds excessive heat. I have looked into the push button lockups and they are spendy, but mabey it will be worth it in the long run. I know that the 4L80E was developed around the stock ft/lbs of the 6.5L, and the peak hp of the 454's, but if my engine was even close to what it was stock I probably wouldn't even stress about it. thanks again!

 

[TimB]

I have a 4L80E in my motorhome. It has 110,000 miles on it, and I have never really kept it from going into OD unless it was shifting a lot. I run the interstate across Kansas about 75 mph in OD - towing my jeep on a trailer behind. That's a excelent transmission for towing - the alison is probably the only better one.

 

[superdave84058]

put another cooler on it, we have a savana at work that we pull 10,000lbs almost daily. We added another cooler and change the trans fluid ever time we change the oil. We have had no problems with it, it shifts smooth and the fluid is never brownish.But it is a 5.7 gas not a diesel. the guys who build our transmissions for our box trucks wont warrenty them if we dont put the extra cooler in.

 

[Rot Box]

thanks for the info guys! Unfortunatly between a massive 4 core radiator, huge engine oil cooler, power steering cooler, A/C condenser, and of course the factory trans cooler there is no room for anything else, probably one of the reasons that the 6.5L's didn't come with a factory intercooler, but changing the fluid that often is a good idea. Mabey I should invest in a ATS or BD trans pan with extra capacity and a drain plug. Thanks again for the help!
P.S. I can't believe that the 4L80E and many others don't come with a factory drain plug! every time I change the fluid I end up wearing half of it!

 

[Tacoma]

I can't believe you haven't added a drain plug after the first fluid change! Shocking. heheheh

There is room. I ran a big B&M plate cooler in front of all that and had no trouble on a big box van. Didn't seem to hinder anything. You can also get the framerail style ones, they're not the greatest but any little bit helps, or a remote one w/fans.

Cooler is better.