Well another question about this stuff. I understand you should NEVER tow in overdrive, to my understanding for the reason that it is not as strong as other parts of the transmission, added to the fact that the engine isn't in its optimal pulling power RPM.

Currently running 3.55 and 33.5in tires with a 5.2 so shes a dog, without a trailer. I have a hemifever tune, FI Hughes Airgap, CAI, no cat and a muffler, if that does anything.

Nonetheless I want to change to 4.56 gears which with my tire set up at
70 mph in O/D : 2214 RPM
70 mpg out of O/D : 3209 RPM

I'd like to cruise at about 65-70mph with the trailer but not run at 3200 RPM the whole way. Basically what I'm curious about is, how detrimental would it be to tow 4000-5000lbs in overdrive, atleast down hills, and when I need the power I have no problem turning O/D off and running about 3000RPM for a minute or two and then just back to Overdrive to cruise in. Thanks.

 

Just don't do it. It's got nothing to do with the strength of the overdrive unit or the engine's optimal pulling range, and everything to do with the fact that you destroy the transmission that way.

 

Yup. In O/D, the trans generates more heat. Towing puts more stress on the trans in any event, which equals... more heat.... combine that with O/D, and you burn the fluid fairly quickly, and the trans follows shortly thereafter.

 

Compromise with 4.10's? Still a bit doggy but lower RPM's.

 

And add in greatly accelerated clutch wear, the friction material added to the oil by it, the mostly undetectable mechanical shocks those slipping clutches deliver while you're tearing the friction material off of them, and the stresses the hard parts weren't designed to withstand forever, and it's just a big bag of Don't Be A Fool with a side order of You Deserve What You Get If You Do seasoned to perfection with You've Been Warned.

In my world, fuel is easier to pay for than transmissions.

 

I gotcha, I believe you, but what exactly do you mean destroy the transmission?

 

Now what if I got one of those heavy duty transmission coolers with a fan on it, and it kept trans temps without a doubt under 180?

I have a tranny temp gauge that is right in the line coming out of the tranny right to the cooler so I get best instant readings and never let it get over 200 thats when I pull the truck over and throw her in neutral.

 

I thought about it, but I was told if I'm going to do a gear change thats not much of a drastic change and 4.56 would give me that acceleration right off the line, I don't plan on towing often, but I think 4.56 would give this 5.2 right in the RPM range it wants to be in and make my driveability awesome.

 

You bring up a good point.. I don't beat on her very often, I actually get called the Grandma of drivers for that reason. But what if the temperature on the tranny in general was just kept down?

 

problem with towing in od is the thrust washers on the planateries
even cool oil is not enough
on my tranny we drilled the shaft and all the passages
installed half inch diesel size hoses and a 100 fin platecooler with half inch in and out
this cut the backpressure measured at the trans output from 45 lbs to 5 (mush more flow)
but biggest trick was to install the diesel straight cut planetariums which generate no thrust. The later low angle helical planataries are better but not perfect
you can also install the stronger better transgo OD spring and diesel number of clutches
I tow in OD all the time but would not without diesel guts
we are talking RE-RH here
in any case do not lug your motor down
better to let it spin at light throttle than lug at more throttle even if the lower rev solution gives slightly better mileage= but don't drive with it reved way up either