68rfe

[jacknife]

Just finished a run to Az with my 2014 3500 SRW Mega cab pulling a 36 ft 5th wheel with a 50 gal Transfer flow tank trl weighing about 13500 loaded. Going home on I-8 you have to pull a 6% 9 mile grade to the top. It was 87 degrees went up locked in 4th about 52 mph transmission never got over 174. Just wanted to share this info with those that are undecided on which transmission they need. 342 gearing 6 speed pulls great! Oo.

 

[RVTRKN]

I don't like the way it shifts when putting around in traffic, the 3:42 rear is too low for this, keeping my RPM's at 1250 and lower RPM's. When getting on the throttle it responds well and like the feel of it, when RPM's are over 1500. The clunky feel that has been complained about by others happens when @ accelerating and someone cuts you off and you have to let off the throttle then back on the throttle. I have been testing mine for optimum MPG with T/H on and off and EB on and off and in auto, at every tank fill up. However I'm going to extend the the length of the tests to 1000 miles. I believe I'm confusing the computor, as they have an algorithm and learn the different driving style for the individual. Mine seems to be getting worse in the way it shifts, so I'm extending the test periods. BTW, it runs very cool no matter what, in traffic or cruising at 70.

 

[Cummins12V98]

I don't like the way it shifts when putting around in traffic, the 3:42 rear is too low for this, keeping my RPM's at 1250 and lower RPM's. When getting on the throttle it responds well and like the feel of it, when RPM's are over 1500. The clunky feel that has been complained about by others happens when @ accelerating and someone cuts you off and you have to let off the throttle then back on the throttle. I have been testing mine for optimum MPG with T/H on and off and EB on and off and in auto, at every tank fill up. However I'm going to extend the the length of the tests to 1000 miles. I believe I'm confusing the computor, as they have an algorithm and learn the different driving style for the individual. Mine seems to be getting worse in the way it shifts, so I'm extending the test periods. BTW, it runs very cool no matter what, in traffic or cruising at 70.

Every time I drove my 11 Dually I hit EB and TH. Trans always shifted great no lugging when you wanted to accelerate. Never a problem in 65K towing a combined 29K all with 3:42's!

Trans never exceeded 192 on long 6% grades in 100 degree weather.

All that said I really like the Aisin with 4:10's so far.

 

[RVTRKN]

I have to track the MPG for the company, and they questioned the use of EB with T/H. So I'm tracking the MPG, and hope it's not much different. This is a company owned truck they bought for me, so I have the follow the rules.

I'm sure the Aisin is much better, however I would want to drive one for a long trip before I purchased one. The G56 would be my second choice if I didn't like the Aisin. As much as I hate the G56, driving my 68rfe has cured me of auto's if I can't get the Aisin and if I like it. The 3:42 is to low for my liking, I hate the pinging of the CTD and shudder in the 68rfe in mine makes, and is why I like T/H but even then it can ping and shudder.

 

[gsbrockman]

I have to track the MPG for the company, and they questioned the use of EB with T/H. So I'm tracking the MPG, and hope it's not much different.

As a suggestion....try the EB in the "Auto" mode for a few days. I like the Auto mode if I'm traveling unloaded......if I have a trailer behind me, it's in regular EB mode.

 

[RVTRKN]

I'm currently checking that out now and have 100 miles so far, it does better in allowing me to coast W/O losing momentum.

 

[Newsa]

http://www.cumminsdieselspecs.com/67.html

Does anyone know why the Cummins with G56 gets max torque at 200 rpm lower than some of the autos?

I assume it's OK (safe on Cummins) to pull light a load all the way down to 1250-1300 before down shifting?

I have only pulled up to 5500 lbs. (Light travel trailer through tge smokeys). Only once did I get a shudder when getting down to 1200 rpm's
with my G 56. Engine temps/oil temps maxed out at 212-215 only once.

I've seen some places where the max torque is listed at 1400 rpm for the g56.

but the document above it says max torque @ 1500. It must be safe to drive 150-250 rpm on both sides of the max torque?

Of course with the g56, its easy to drop into 5th at the first hint of a shudder. And I do.

Just curious about why the different specs for the same engine. Since I've never driven a 68rfe or Aisin, just curious at your experiences and observations of how the engine and transmission work together.

I always thought that manual trannies would get better mileage than automatics. That was probably true in the 1970's & 80's. But with locking torque cinverters, I think your autos might do a slight better by achieving a lower cruising rpm at a comfy 70 mph.

 

[Newsa]

http://www.cumminsdieselspecs.com/67.html

Does anyone know why the Cummins with G56 gets max torque at 200 rpm lower than some of the autos?

I assume it's OK (safe on Cummins) to pull light a load all the way down to 1250-1300 before down shifting?

I have only pulled up to 5500 lbs. (Light travel trailer through tge smokeys). Only once did I get a shudder when getting down to 1200 rpm's
with my G 56. Engine temps/oil temps maxed out at 212-215 only once.

I've seen some places where the max torque is listed at 1400 rpm for the g56.

but the document above it says max torque @ 1500. It must be safe to drive 150-250 rpm on both sides of the max torque?

Of course with the g56, its easy to drop into 5th at the first hint of a shudder. And I do.

Just curious about why the different specs for the same engine. Since I've never driven a 68rfe or Aisin, just curious at your experiences and observations of how the engine and transmission work together.

I always thought that manual trannies would get better mileage than automatics. That was probably true in the 1970's & 80's. But with locking torque cinverters, I think your autos might do a slight better by achieving a lower cruising rpm at a comfy 70 mph.

 

[RVTRKN]

First of all, you should never pull a grade in sixth with the G56 with a load, even with a light load. Second, the 3:42 diff in my opinion is too low and allows the CTD to run under its sweet spot of 17-1900 RPM's. My truck with its lower HP & Tq of 305/610, can pull 23K GCVW at 21-2300 RPM both directions over the Grapevine with ease. And caution you not to lug your CTD, if you don't have an EGT gauge, or never for that matter.


I've never experienced any shudder with my G56. But I have not allowed my RPM's to go as low as you have. And with 3:73's that I think are too low for the G56, and think that the EPA has a lot to do with Dodge going to 3:42 diff's, it is detrimental to the CTD, G56 and differential.

I recommend you keep your RPM's in the sweet spot for the CTD, the G56 and 3:42 are not changeable, but with good maintenance can last a life time.

 

[Newsa]

I agree, I shouldn't lug the CTD. It was my first tow and after having the truck for 9 months, was testing it's ranges and becoming familiar with it's torque curve and power band. In fact, I downshifted at the first hint of a shudder. Something that it sounds like the 68rfe may not do. My exhaust gas temps wouldn't and did not get high enough to damage the exhaust heads.

I agree that the weak link in the power train is the g56. That's why I'm surprised with you picking the g56 as your second choice in a transmission.
I love my g56. And it will serve me fine with the light towing I do. Any towing I do, could be accomplished with a 1/2 ton. But I like the feel of the CTD, and love the towing gas mileage. I borrowed my parents gasser RV with the ford V10 and it sucked gas like a 79th street hoe.

As for the differential, The 3.42 puts me right at the sweet spot of 1700-2000 rpm's while traveling highway speeds of 55-70 mph. Also, with the light towing I do, I'll never tax that heavy duty differential.

I will definitely use 5th gear this year when pulling the same rig through the smokies. I will be more cautious than last year with the transmission and possible EGT's
I don't have an exhaust gas sensor, but know that EGT's can sky rocket quickly. My oil & coolant temps never got above 212. The grades were mostly short before giving the drive train a breather. I really only had one long grade where I buried the pedal and blew out the cobwebs.

RV, thanks for your input. I've learned alot from you over the past year.

 

[gsbrockman]

I don't have an exhaust gas sensor, but know that EGT's can sky rocket quickly. My oil & coolant temps never got above 212. The grades were mostly short before giving the drive train a breather. I really only had one long grade where I buried the pedal and blew out the cobwebs.

On a stock truck----EGT's will never be an issue. It's only when tuning or programmers are introduced that EGT's can become problematic.

 

[Newsa]

Yeah, used to be able to burn heads on stock vehicles. Can't any more. No tuner here. Cummins is bulletproof. G56 is the weak link.

 

[RVTRKN]

You might want to get a temperature sensor for that G56, mine can run hot, but I only know the temps after the conversion. Browned bearings was the tell tale signs it ran hot.

 

[Powder Extreme]

All this talk about not lugging, yet since the stupid transmission is PROGRAMMED to lug the motor, apparently Ram isn't that concerned about it. My 68rfe will up shift in t/h mode with a trailer hooked up dropping the RPM to 1000-1100. Far to low of rpm in my opinion, especially loaded. Empty in regular mode it will up shift me down to 8-900 rpm and cause the truck shudder.

In my opinion, anybody who loves their 68rfe has never experienced an Aisin or an Allison. Having owned all three, the 68rfe pales in comparison.

 

[RVTRKN]

Yes, Im aware of that phenomena now, I am learning faster than the trans learns. If I'm concerned about the RPM's, now I manually shift the trany as the highest gear allowed to keep the RPM's where I want them. But what a PITA, I'm starting to like my G56 more and more. :-laf:-laf:-laf:-laf:-laf:-laf

 

[Newsa]

Does the torque converter lock up below 1000 RPM? That sounds weird.

 

[RVTRKN]

I don't know if it's locked, but I cant stand the pinging.

 

[Bob4x4]

Yeah, used to be able to burn heads on stock vehicles. Can't any more. No tuner here. Cummins is bulletproof. G56 is the weak link.

Lol I never saw a burned head on a stock Ctd.

 

[Newsa]

Me neither. Only on gasser ' s built in the 70's & 80's. Electronics fixed that problem in the gassers. Cummins has only been supplying engines since 89. Early Cummins had manual injectors. But that long stroke helped insure fuel wasn't still burning as it came out the manifold