Engine/Transmission (1998.5 - 2002) How come I cannot keep low rpms with an auto ?

[Valv]

For some strange reason I have stuck in my mind low RPMs means less fuel, and less stress on motor.

I don't like much motor revving up to 2700rpms to have good power behind, it's a lot of fuel, noise, and motor running.

Why we cannot have good power at lower rpms, like 1700 and keep running truck in the low end of the tach instead of opposite.



It feels I am wasting a lot of fuel just to move ahead.



Are auto transmissions not made to run low rpms ?

 

[csutton7]

maybe it's time to rebuild that transmission--or how about putting it in 1st and then manually shifting it to 2nd and then to 3rd---chris

 

[Nyoest]

I had the exact same thoughts as you keep the rpm down = better mileage but from what I understood from the previous TDR mag's fuel consumption graph in the article about 12v VS 24 v horse and torque, our engines actually use less fuel between 2100 and 2300 rpm rather than at 1800. I've adjusted my driving style :-laf to keep my rpms in that range at all times and I have picked up almost 1 mpg. You might have other issues with your trans though





my . 02



Neal

 

[dieselbomb]

If you wanted to keep the RPM down you should have bought a truck with 3. 54 gears not 4. 11 . You got the towing gears not the mileage gears, although I see around 19-20 mpg pretty consistently

 

[fox]

I think the answer to your issue is this.

Dodge puts a loose torque converter in the Cummins equiped truck to protect the auto. They didn't have confidence in their trans at low RPM.

The aftermarket trans shops can fix the issues.

In a nut shell, trans failures are from internal leaks( from quality control issues) and low apply pressures.

All this is from mass production. A good trans builder understands this.

You can see my profile and mine is fixed.

I have pulled 8,000 lbs at 60 in OD (which is 1500 rpm) with no slippage. Now, I should say this too, low rpm, like my 1500 is not recommended because it is hard on the flex plate. The Cummins has a lot of combution pulsations and this can break the flex plate.

 

[zstroken]

What internal leaks are you referring too? I was unaware that anybody really other than one rebuilder rants and raves about internal leaks. The other rebuilders pretty much use the stock parts in there rebuilds with increased line pressure, better torque convertors and substancinally modified shift circuits. Heck if I recall most of them used one extra clutch plate in the front clutch, which is in the 48RE. The pumps on these trannys is a positive displacement style pump. If it is unregulated the pressure can exceed 1000psi. It has ample fluid capacity so unless there is a huge internal leak i don't think there is a problem. I mean I know several rebuilders that push big power through there transmission's and don't change anything but the convertor and the VB. As something breaks(input shaft) then they change it. How many planetary failures have people reported?

 

[dieselbomb]

That is all irrelevant. Once the transmission goes into lockup the TC no longer has much effect, unless, you are overpowering the lockup clutch in the TC. Like I said 4. 10 gears rev higher than 3. 54 gears which is what 85% of all these trucks were shipped with. You got 4. 10 gears. I am guessing because yours was prepped for snow plow option or heavy towing. 3. 15 tires will get you back to about a 3. 72 corrected gear ration but you would need 37 inch tires to get back to 3. 50 ratio.



FYI I believe the difference between the two ratios ends up being about 375 RPM at 70MPH

 

[Tom W]

This is what's wrong with the stock transmission, you can't get the power to the ground until lockup. Drive a truck with a DTT transmission and you will see a world of difference. I can drive all day and never get over 2000 rpm and still beat almost everyone else up to 70 mph.

 

[jtwcummins]

From what I know of the 47re alot of them lose pressure from the pump thru the transmission. Not much, 3-5 lbs, but it can be an issue. This pressure can be increased but not to much stock. The TC is a major weak area. It isn't built to take the CTD's torque curve. Essentially it is designed more for a gasser, aka V10. Another problem is the fluid flow increases with throttle pedal position. My exhaust brake has a vac unit that applies full flow when the brake is on. In park or at idle in gear the flow is almost non existent. If you have a trans temp gauge you will be surprised how fast the temp goes up in city driving.



If you try and tow at low rpms the flow of fluid in the transmission is low and maintaining TC lock w/o slippage is impossible. Things work best around the engines sweet spot, 1800-2000 rpm for 12v and about 500rpm higher for the 24v. I defuel at 2600-2700 rpm so with 4. 1 gears 85-90 mph is basically all there is and running over 2k fuel economy goes in the tank.



As far as the 47re being a Torqueflite upgraded alittle I ran with Mopar dudes with 413 and 426 wedge and hemi ramchargers. The dual quad, 13. 5-1 compression and at least 4. 56 or 4. 88 gears. Never had a transmission problem, and they we beat hard. Things don't really start happening in those engines until rpm goes up. The CTD starts putting out torque when you take your foot off the brake and it goes up fast.

 

[fox]

What internal leaks are you referring too? I was unaware that anybody really other than one rebuilder rants and raves about internal leaks. The other rebuilders pretty much use the stock parts in there rebuilds with increased line pressure, better torque convertors and substancinally modified shift circuits. ]



Maybe this is why there are few failures of this trans company??? Could it be they are addressing the CAUSE of failure. BTW, there is more than one good transmission company. It is about putting the pressure where it does the trans some good, and keeps it solid thru out.

 

[TCDiesel]

I Don"t Post Much in 2gens I see that you guys know your transmissions,The stock TC is about 78% efficient most upgrade are 91 - 93% efficient.

 

[Valv]

Dieselbomb I can't change tires I have a dually, if I go up 1 size that's it, changing gears it's expensive (it's a 4x4 too). But still would like less rpms, I guess my call to Mr Goerend will be very soon.



Jtcummins I like your reply, thanks. .



Thanks everybody, I guess I should have bought a 6 speed, but I've got this truck used, and price... ... I don't think many can beat me on this... . very low.