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Discussion Starter · #1 ·
Yeah, newbie here. Still learning.

Question just hit me - based on some things I think I remember reading on the forum.

Does the converter lockup in 5th & 6th? Seems I read something that if the trans heats up too much one should limit it to 4th gear so it locks up, or some such thing? Or did I read or remember that wrong? Seems it should lock up for mileage in OD, too.

And when one selects TOW mode, does that do anything other than increase rpms for upshift and downshift points, particularly into OD gears?

Thanks!
 

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The Auto Transmission locks in 3rd through 6th. It needs to be above 70 degrees (trans. temp) which means it may not lock up at first when it's cold out. I think I've mine lock up in 2nd before but I don't remember the circumstances. Also I don't usually see the lock up below 25 mph which means a slow hill climb in the hills can make things warm up quickly. if I use 4 lo I can lock up at a much earlier speed but I limited to about 15 mph. So - up to 15 mph in 4lo if I'm on gravel or snow for low speed and above 25 in 2 or 4 hi or watch the temps.

I think what your might have heard is that when the auto trans goes into limp mode it will go from 1st directly to 4th and wont lock up
 
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When towing up a grade, it is helpful to use a lower gear, but not to allow lockup.

On steep grades at low speeds (like 25 mph or below, as on switchbacks, etc.) drop it all the way down to 1st gear if possible. This reduces the slippage within the converter (even though the TCC is not locked up), which will greatly reduce the amount of heat generated inside the converter. In 2nd gear, the TCC will lock up, but generally (when towing on a steep grade) this will drop the torque so much that the truck will slow down, which will cause the TCC to unlock again. And if you pull a grade in 2nd gear (unlocked), you will cook your converter a LOT faster than you will running in 1st gear.

At higher speeds (45+ mph) it is good to drop it down to 4th gear when pulling a grade. The TCC will lock in 4th (or 5th, or 6th), but here the concern is the OD clutch. Using 4th gear will put a LOT less torque on the OD clutch (than using 5th or 6th), which could greatly extend the life of your trans.
 

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Discussion Starter · #4 ·
Bingo! That's what I was primarily looking for. In the next few months I'm pulling 7k to near 10k up the mountains West of Denver and East of Salt Lake, up to 6% grade and several miles long.

For that reason, and the 180 k on the vehicle, I got a RevMax 550. Didn't want to take any chances. Used to run big rig in those areas and Montana and Idaho and more than once was saved by preparation and knowing the vehicle capabilities and how to run it so I didn't try to make it do something that would harm it.
 

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When towing up a grade, it is helpful to use a lower gear, but not to allow lockup.

On steep grades at low speeds (like 25 mph or below, as on switchbacks, etc.) drop it all the way down to 1st gear if possible. This reduces the slippage within the converter (even though the TCC is not locked up), which will greatly reduce the amount of heat generated inside the converter. In 2nd gear, the TCC will lock up, but generally (when towing on a steep grade) this will drop the torque so much that the truck will slow down, which will cause the TCC to unlock again. And if you pull a grade in 2nd gear (unlocked), you will cook your converter a LOT faster than you will running in 1st gear.

At higher speeds (45+ mph) it is good to drop it down to 4th gear when pulling a grade. The TCC will lock in 4th (or 5th, or 6th), but here the concern is the OD clutch. Using 4th gear will put a LOT less torque on the OD clutch (than using 5th or 6th), which could greatly extend the life of your trans.
Pretty much everything TransEngineer says should be a sticky on this forum. :thumbsup:

Great advice.
 

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Discussion Starter · #7 ·
X 2. He alerted me to the possibility of reduced lockup pressure due to valve body bore wear in high miles units when I first found this forum and started asking questions about any concerns I should have about things, incl the transmission, and what to do about any possible problem areas.

That started my path forward to the RevMax 550 I have now. I'm glad that I ended up with it. I ran big rig all over between Chicago and Seattle/Denver/Salt for a while a number of years ago and learned very early that anything I could do to minimize the possibility of breakdowns on the road was well worth it.

I just finished learning the trans a few days ago and have driven it a little more aggressively just to experience the shifting, and I have to say I couldn't be happier with it. I've built several automatics over the years into upgraded street performance trim but this is an entirely new animal for me and was very glad to have knowledgeable advice. Now I have peace of mind on that important item.
 

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What rear gears are you running? I have 3.73 and tow a 16K 5th wheel. I lock it in 5th on the level and run about 2100 rpm at 65. In tow-haul it seems like the 2nd-5th shifts are "mushy", so I try to get up to speed as soon as possible. I didn't have any over temp codes last summer in the heat. Any torque converter generates more heat through the fluid coupling until in lock up.

I have a PML pan and trans temp gauge to add this year before going out. I'm new to towing heavy also.
 

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Discussion Starter · #9 ·
3.73's and stock size tires, the larger of the 2 options, and a new RevMax 550
that comes with a deep pan and a heavier duty converter than stock.

Just got done with a trip over the hump west of Denver and then all those hills from there to Vegas, but only towing about 4k.

I had to downshift to 5th on some of the longer and/or steeper hills after I got over the hump, but did it mainly to keep rpm's at/over 2000 to reduce strain on the lockup and hi trans temps. Have a CTS, didn't see over 145 trans temp even up the steepest hills when I got down into 3rd for awhile, and even after it warmed up into the 60's. In colder temps, with just 2 holes open in the winter front, I saw mostly 130's max.

I didn't notice any particular mushiness in those shifts, seems like the Tow Haul focuses a lot on running the rpms up higher before the shift. But that was with the RevMax. Shifts were still nice and firm, even without putting my foot into it too hard. No harshness or shocking on the drivetrain, but not mushy either.

Don't have any experience towing with the stock trans, and not with any serious weight yet.

You might want to consider a trans temp gauge. temps are critically important to an automatic, and are a good guide on how to drive it while towing.
 
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