Can someone please explain this or provide a useful link.

This is my first Diesel, and I'm not getting used to this weird 48re doing it's own thing and I'd like to understand what's going on and why it feels so much more different than the auto tranny in my 03 1500 Hemi.

 

Well its a 4 speed auto with tow haul feature. When you push button on end of shift lever you activate tow haul. In tow haul mode the shift points are raised to a higher rpm for moveing out a heavy load. Also if you hit the button at say 50 mph while trans is in 4th gear it will downshift to 3rd. but then will shift back to 4th as soon as the trans sees fit to do so. Also in tow haul mode you have downhill motor brakeing . Trans will downshift as you go down hill automaticly to help hold load back. To be effective doing this the torque converter clutch must be locked up to keep motor locked to wheels, same as a stick shift. The tow haul mode does this for you. In regular mode when you let off throttle say at 50 mph the torque converter relieses and you like freewheel. Not much help then for downhill motor brakeing. Thats about the jist of the way she works.
To help you understand the torque converter and TC clutch ( torque coverter clutch ) . Think of two fans , faceing each other. start one fan and it will blow on the 2nd fan making it turn. OK motor is turning #1fan , #2 fan is hooked to trans. Instead of air between you have trans oil. As you can see there is much variation between fan speeds,as the motor forces #1 to turn . #2 is being held back by the load. Between these fans there is a clutch. Called the torqe converter clutch. It locks the two fans together, so theres no more variation in speed between the two fans. As you get the load rolling and the trans upshifts, eventually the TC clutch locks up and gives you a solid drive between motor and trans.
So as you go downhill this TC clutch must be locked to have downhill motor brakeing. The tow haul mode does this for you.
Another feature the TC clutch does is eliminate heat. As you can immagine the two fans whipping the oil will get the oil hot. Once the TC clutch locks up the fans no longer whip the oil and the oil will run much cooler.
Hope this helps

 

bluepp,
Are you a tranny mechanic? Man, that was an incredible explaination. I didn't realize it's only concerning the tow/haul mode.

Driving slowly and cycling through the gears in regular mode(?), why does it feel like the tranny wants to shift sooner than it it actually does? The rpm's are up there but sometimes it seems like it's not shifting soon enough. Hard to describe. It seems like something isn't quite right, but I think I'm just used to the smoother shifting 5 spd auto in the 1500 Hemi I had previously.

Anyway, thank you very much for your comments. Much appreciated.

 

What your discribing sounds like the tow haul mode. When engine will wind up much higher then nessesary before upshift. This would be good if you got a 10,000 lb trailer back there, but would seem funny empty. You should be able to see or feel a difference between tow haul and normal setting. Especially if you put a load on.
But theres always a chance your unit is not fungtioning right. Like stuck in tow haul ALL the time regardless of button setting.
More food for thought.You say going slow and cycling through the gears??. OK You put shifter in 1st. You take off it stays in 1st. You then put shifter in 2nd, truck should shift right into 2nd, but with the shifter in 2nd position, the torque converter clutch will lockup the TC. Which will take a few seconds and feel like another gear as all TC slippage will be elliminated. Which is what you want for climing steap grade with load too big to clime in 3rd. Now when you move shifter fron 2nd to drive, three things happen, (1) TC clutch releases,engine will pickup some rpm,(2) trans will make shift into 3rd, rpm drop a little, (3) TC clutch will lockup again. And then eventually trans will shift to 4th.
Thats a lot of messing around. This 48re is designed to give you TC clutch lockup in 2nd,3rd and 4th. Where your hemy had 5 gears . it would only lockup in the finnal gear . Clear as mud???

 

Clear as mud! I don't think I've ever had it in the tow/haul mode...at least knowingly. I'll have to see if I can feel a difference. I'd hate to think it's stuck in tow/haul mode and my dumb butt doesn't know it. Usually there is a light that comes on for tow...I think.

These CTD's and 48re's are so different than what I'm used to, but it's growing on me.

 

Are you just asking what is going on based on what you feel?

When you start out the truck will shift from 1st to 2nd, then 2nd to 3rd, then you will get lock up and then it shifts right into 4th. The lock up seems to happen right before it goes to 4th and I think that throws some people off.

 

That is if you put it in drive and let the computer do the shifting. But if you work the shift lever by hand ,you can get 2nd gear lockup.???

 

Yeah but I am lazy.......especially when driving around empty.

 

I always let the tranny do the shifting rather than manually shift with the lever. I don't have anything to tow yet. I wish I did, to help speed up the break-in. I'm about ready to find something to rent for a weekend just to make it sweat.

It seems as though it's normal with the way it sounds and feels when shifting and locking up. It's just so much different than the 1500, but I'll figure it out someday.

 

Well you refered to driveing slowly and cycling through the gears ---- I assumed you were cycling the shift lever by hand . If you were just letting the trans upshift by its self ,thats quite different. They do react quite different then a gasser.
My 98 with 4.10 gears ,when takeing off slow fron a light will upshift to 2nd within 10 feet and shift to 3rd by the time your through the light. You really must be paying attention or you'll miss the 1-2 shift. The motor rpm hardly change at all. Quite confusing untill you get used to it. By the time you get to 30 its in 4th and will go into lockup at 40 mph.

 

Good posts bluepp.

DISCLAIMER : The following post is a semi rant.
Guys, you have got to get out of the "get in and drive it" mode. If you have never used the tow mode, or 4 wheel low, or 4 wheel high, then you haven't read the manual and you don't understand what your truck was designed for and how it is to be used correctly. If you expect these vehicles to perform then don't you think you should know how and when to use the design features?

 

Whats with this disclaimer????? The diesels react different then gassers. Its Dirteaters first diesel, he just asked a question!!!!

 

Geico266,
I'm not sure what that was all about, but I have read my manual, and ofcourse I don't understand it all. It's a sharp learning curve.

We're not all mechanics that know the do's and don'ts of these trucks. We're not all ranchers, farmers, or construction workers that use our trucks daily for a good workout. I got mine in hopes of purchasing a toy hauler someday soon to tote around dirt bikes. So far, it's simply a daily driver as I only have around 5000 miles.

As far as this comment:

That's exactly why I'm asking about it, because I want to know how it works. I'm relying on the good folks at DTR's experience. Isn't that what this forum is for...to learn about our trucks. Remember your first Diesel? This is my first and I want to understand it more. I'm sure there are thousands here in my same boat - their first Diesel.

My original question was "can someone please explain this or provide a useful link". So far, you've done neither.

Thanks for your LAME input.

 

Thanks bluepp for your input and understanding that some of us need some help.

 

Geico,
Waiting for my education; when to use 2WD 4HI 4LO, Tow Haul ext. Be specifice, Mud, Mid mired, Sand, Silt, Clay. Nebraska Flat, you need tow haul there?

Thanks
Jeff