Humblecowboy

Been searching here and haven't found the answer to something that I've been curious about for quite awhile. That is, at what weight range is it wise to lock out the OD on my 99 DRW all stock with the auto trans? The most I've pulled with it still in was about 10k. 8k of calves going to auction and about 2k of trailer weight. Getting ready to move some things about 60 miles from our old place and the weight will probably come in at maybe 7k. It's mostly flat terrain down here in SE Texas so there aren't any steep climbs I'll need to worry about plus it's going to be about 98% highway running. Any suggestions on whether I should lock it out and if so what should I keep my max speed/rpm at? Thank y'all for any suggestions you have. Frank

KATOOM

Simply put.....OD in any transmission generates heat from the change in compound gear ratios. So towing in OD only exaggerates the heat issue depending on the weight towing, aerodynamics of the trailer, weather, terrain and HP over stock.

Meaning, if its cold out, you're not towing heavy, the road is flat, and the trailer is not the size of a freeway billboard, then you're more than safe to run in OD.

But if the weather is hot, you're towing at or above the trucks CGVWR, in the hills, and the the trailer is anything but aerodynamic then you'll want to refrain from OD and use 1:1 direct drive ratio in that transmission.

Lastly, transmission fluid temperatures "sustained" for periods of time above 200* are getting warm. Above 225* and things are really hot and at the limit of thermal breakdown and oxidation rate. Get anywhere near 240*-250* and you're cooking things and should change the fluid immediately. Point being, install a transmission temperature gauge and you'll tow with your mind more at ease knowing whats going on.

j_martin

I have a built up A518 transmission, with a low stall TQ, and a frame mounted fan cooler. Transmission man put AmZoil in it, and told me as long as it's cool (ie, the cooler doesn't fail) that it'll run full throttle in whatever gear is needed, including OD till something else breaks.

Common sense will tell you that shifting in and out of OD under full load wears the OD clutch parts each time, so allowing that to happen frequently on long hills could get expensive.

KATOOM

Yes, NEVER let your transmission "hunt" for gears on its own. Doing so is very bad and will result in excessive wear and increased temperatures.

Humblecowboy

Thank you two for all the info. Your responses answered all of my curiosities about this trans. I had a trans flush and filter change done about 20 to 25k back so I think I'm good there for a few more miles. Since I'm going to be pulling round nosed stock trailer in flat land territory with ambient temps between 75-85 I should be good on my trans temp. And yes, a trans temp gauge is on my list of must haves for this thing. I have the FP/Boost and exhaust temp pillar mount gauge set but haven't installed yet. Yeah, go ahead and kick me LOL. This truck has a dual trans cooling system. One air cooler next to the AC condenser and a water cooler up behind the turbo next to the block. I did have an issue once where when I put it in drive after it sat parked for a little over a week that the trans didn't want to catch. Slipped into neutral then back to drive and it caught normal. I did find that my crank sensor was bad so I replaced it and that solved my gear hunting between about 48 and 55 mph. I had cleaned the grounds several times and it helped for a short time but started again. so far so good. I had never heard of the crank sensor causing the gear hunting but I reckon it can. Thanks again for all of y'alls knowledge, Frank

j_martin

The lower gears are all hydraulic controlled in the transmission. overdrive is controlled by the PCM, and one input is the CPS. Makes sense a flaky one would make the transmission erratic.

I think you worry too much. Drive it.

KATOOM

A notorious issue with these trucks is while the alternator is generating DC voltage, the diodes can also generate excessive AC voltage. That excessive AC noise will cause electrical phantom issues with sensitive neighboring electronics, like the APPS, VP PSG, and transmission solenoid. Its not always easy to know its affecting the APPS or VP but it will typically cause the transmission to rapidly lock and unlock the torque converter which will seem like its constantly hunting for gears.

People have been known to install AC filters but those are merely masking the problem. The only way to solve the issue is to test the alternator yourself (since no parts store will) and determine the AC voltage levels. If they're excessive then a new alternator is the fix. And.....quality alternators are highly suggested since the auto parts store stuff is usually sub par quality.

SOhappy

I realize the OP's truck is all stock, but I'd still recommend running a trans temp gauge. Cheap insurance. The 47RE isn't known for being able to take a lot of abuse as delivered from the factory. Keep the trans under 210° and you can squeeze some life out of them though.

Humblecowboy

Yeah, you nailed me good on that one j martin. I can't help it I reckon because I love that old truck almost as much as I love my Waf. More when she's mad at me LOL. Funny you should mention the alternator KATOOM. The one in the truck is OEM and I have been considering going ahead and replacing it since I have read a lot on here how they can create nightmares. I do feel better that j martin reaffirmed my suspicions about the CPS. So I guess to make sure I get a quality one I should go to the dealer$$$$$. The trans temp gauge is definitely one of the top priorities. I told my daughter that the truck is my hearse and that she is the only one allowed to drive it. Thank you guys for all the help and piece of mind and I'll try not to worry about it too much. Frank

Busboy

I might add I've never really seen the reason for the fancy finned aluminum transmission pans but after getting covered with oil on my last oil change I installed an after market one with a drain plug. It alone dropped the transmission temps 12degs while towing heavy.