Towing with 3.42 ratio

[mikel]

Ok, here's the deal. I'm looking at a truck that has the 6. 7 and 6-speed automatic, but apparently someone ordered it with the 3. 42 rear axle. Does anyone have this combination and how does it pull? I have an approximately 11,000lb 5th wheel and I don't want to make a mistake buying this truck to pull this trailer.



Thanks!

Mike

 

[TAbbott]

With oem size tires, I think it would probably do a pretty decent job. The 6. 7 makes peak torque clear down at 1400 rpms (I don't know how low the auto transmission will let it pull) some 200 rpms lower than the 5. 9. If the transmission shift points are such that it will let it pull to 1500 or 1600 before shifting, I think it would work pretty well and even deliver reasonable fuel mileage when not towing.



Will it pull as hard in a particular gear as it would with 4. 10's? Nope, but it would still get the job done pretty well even if it was in direct gear when it did it and I certainly don't think you'd be dropping gears on every overpass or something like that.

 

[mikel]

Thanks for the feedback, I'm hoping it'll do ok. I think I got a decent deal on it so we'll see how it works out.

Thanks again!

Mike

 

[Bhale]

Please let us know how it does as i'm considering ordering an '09 in a few months and that 3. 42 looks pretty good right now. If my math is correct, the 6sp auto with 3. 42 rear will give you 66mph at 1600 rpm where as the 3. 73 would get you 61 mph at 1600 rpm. (based on a tire diameter of 30") That's the full 650ft/lbs torque at 1600rpm, not to shabby!



Brian

 

[HBarlow]

Please let us know how it does as i'm considering ordering an '09 in a few months and that 3. 42 looks pretty good right now. If my math is correct, the 6sp auto with 3. 42 rear will give you 66mph at 1600 rpm where as the 3. 73 would get you 61 mph at 1600 rpm. (based on a tire diameter of 30") That's the full 650ft/lbs torque at 1600rpm, not to shabby!



Brian

Well, I hate to disagree with the above opinions but I would not buy a 3. 42 geared truck for towing. Use Klenger's gear/road speed calculator and you'll see that when you combine a 3. 42 gear with the new 68RFE transmission fifth and sixth gear will be useless when towing unless you plan to tow at 70 mph or better.



My first Dodge-Cummins, an '01, was intentionally ordered with HO 6 speed and 3. 54 gears. It was great for pulling an 8,500# Airstream or Avion which I owned when I bought the Dodge. But later I bought a used Travel Supreme fiver with a GVWR of 14,500#. The old Dodge would pull it but it grunted and groaned getting the load moving from a dead stop. It was not pleasurable to drive when towing the trailer. It also was not geared ideally for towing in CA or IL which have 55 mph speed limits when towing. At 59 mph I could keep it just barely on the edge of the torque peak at 1600 rpm. Often I had to downshift to run in 5th direct. Pulling a lighter trailer or running empty it was geared perfectly. Personally, I recommend 4. 10 gears for towing anything but very light trailers.



When I bought a new '06 with 48RE I ordered the 4. 10 gears. 4. 10 gears work great with the new 6 speed automatic transmissions.



But each to his own. If 3. 42 gears are your choice I rest my case.

 

[Vaughn MacKenzie]

Well, I hate to disagree with the above opinions but I would not buy a 3. 42 geared truck for towing. Use Klenger's gear/road speed calculator and you'll see that when you combine a 3. 42 gear with the new 68RFE transmission fifth and sixth gear will be useless when towing unless you plan to tow at 70 mph or better.

Who says you have to tow in 5th or 6th? Direct (4th) would be just about right with the 3. 42 gears, especially with 11,000 lbs in tow. 60-65mph puts you at 2200-2375 RPM, a far better RPM range to operate at than 1600-1700. Fifth could be used at upper 60s-70mph on the flat with no headwind, that's about 2000 RPM. 6th is definitely a No-Tow gear no matter what rear axle you get

The biggest concern with 3. 42 gears is rear axle temp. . . I'd put some 75W-140 syn lube in there and have a temp gauge.

 

[CUMMINZ]

You will stay in 5th a lot that is for sure. With that gear even when you are running in 5th and 6th you will be downshifting every little hill.

 

[WOT]

If you do get it and the gears aren't quite right with the auto I bet you could find plenty of members with early G56 trucks willing to do an axle swap...

 

[mikel]

Good information here, I've been looking at the gear/speed calculator and it looks like:



4th with the 3. 42 is pretty similar to 5th with 4. 10



5th with 3. 42 looks to be a little shorter than 6th with 4. 10.



6th with 3. 42 looks to be too tall to be useful when towing.



I know my '96 with 3. 54's and 5-speed pulled a trailer this heavy quite well. It was BOMBed a bit, but probably pretty close to what this truck is stock, so I'm hopeful that this one does ok.

If you do get it and the gears aren't quite right with the auto I bet you could find plenty of members with early G56 trucks willing to do an axle swap...

I have actually considered this. I'd hate to start wrenching on a brand new truck but it's definitely a possibility.

Use Klenger's gear/road speed calculator and you'll see that when you combine a 3. 42 gear with the new 68RFE transmission fifth and sixth gear will be useless when towing unless you plan to tow at 70 mph or better.

I generally run 65-70 towing on the flats, looking at the chart am I mistaken to think that this truck will do that at about 2000 rpm in 5th? My previous Dodge truck really seemed to like 2000 RPM, did they change something recently that will make this one want to be treated like a Ford and run at 2700+ in order to make any power?



Thanks again for all of the feedback, I appreciate the advice and help understanding what's going on here.



Mike

 

[WOT]

Good information here, I've been looking at the gear/speed calculator and it looks like:



4th with the 3. 42 is pretty similar to 5th with 4. 10



5th with 3. 42 looks to be a little shorter than 6th with 4. 10.



6th with 3. 42 looks to be too tall to be useful when towing.



I know my '96 with 3. 54's and 5-speed pulled a trailer this heavy quite well. It was BOMBed a bit, but probably pretty close to what this truck is stock, so I'm hopeful that this one does ok.







I have actually considered this. I'd hate to start wrenching on a brand new truck but it's definitely a possibility.







I generally run 65-70 towing on the flats, looking at the chart am I mistaken to think that this truck will do that at about 2000 rpm in 5th? My previous Dodge truck really seemed to like 2000 RPM, did they change something recently that will make this one want to be treated like a Ford and run at 2700+ in order to make any power?



Thanks again for all of the feedback, I appreciate the advice and help understanding what's going on here.



Mike

Since I have the early G65 I've been considering the 3. 42 swap - if you were closer I'd try harder to convince you to get 3. 42 so we could swap axles! (I'm in NC)...

 

[HBarlow]

... ... ... ... ... ... ... ... ... ... ... . did they change something recently that will make this one want to be treated like a Ford and run at 2700+ in order to make any power? Mike

No, your assumption is correct. The 6. 7 will run great at 2000 rpm. It will pull down to 1600 but it does produce more hp at 2000 rpm. Only Ferds have to be revved to produce usable power.

 

[donnandon]

Who says you have to tow in 5th or 6th? Direct (4th) would be just about right with the 3. 42 gears, especially with 11,000 lbs in tow. 60-65mph puts you at 2200-2375 RPM, a far better RPM range to operate at than 1600-1700. Fifth could be used at upper 60s-70mph on the flat with no headwind, that's about 2000 RPM. 6th is definitely a No-Tow gear no matter what rear axle you get



The biggest concern with 3. 42 gears is rear axle temp. . . I'd put some 75W-140 syn lube in there and have a temp gauge.

I have to disagree with the "6th is definitely a No-Tow gear". We have 4. 10 gears and have been towing our 12. 5k 5th wheel around for about a year now, letting the trans pick whatever gear it wants. Normal highway driving, 6th always wins out. When we hit a small hill it goes to 5th when it needs it. We just got back from a 2500 mile trip down the Atlantic coast and up back through the Smokey Mountains... . the trans temp was around 175-180F towing in 6th!

 

[HBarlow]

My gross combined weight is just under 24k#. If the speed limit is 55 I tow at 59 mph in Tow/Haul mode which means 5th gear. If speed limit and the wind and terrain allow I tow in 6th at about 62 mph. I don't know of any reason not to tow in 6th unless the ECM/transmission computer call for frequent downshifts.

 

[DPKetchum]

3. 42 is NOT a work gear. Its a comuter gear. 3. 73 is the compromise gear. With the new 6 speed auto 4. 10 is not a bad gear eaither anymore. Its not just towing but starting off with a load behind you. Its a gear I'd never consider in my lifestyle period. 3. 42 strains everthing else on the truck pulling any kind of big weight.

 

[Vaughn MacKenzie]

I have to disagree with the "6th is definitely a No-Tow gear". We have 4. 10 gears and have been towing our 12. 5k 5th wheel around for about a year now, letting the trans pick whatever gear it wants. Normal highway driving, 6th always wins out. When we hit a small hill it goes to 5th when it needs it. We just got back from a 2500 mile trip down the Atlantic coast and up back through the Smokey Mountains... . the trans temp was around 175-180F towing in 6th!

I would agree 6th is probably OK for towing if you have the 4. 10 axle, but I was talking about doing it with the 3. 42 rearend ratio. . . definitely too tall of gearing to use 6th for towing significant loads.

 

[mikel]

Hey, just wanted to keep everyone up to date here. The deal fell through on this truck, and I ended up with one that has 3. 73's.

Mike

 

[DPKetchum]

You'll be a lot happier pulling 11k with 3. 73

 

[SBeretz]

Thats great, let us know how you like the new truck with 3. 73's and especially how it pulls. I like the idea of 3. 73's since I would use the truck for both driving empty, to towing a 20ft flat trailer with quads, to pulling my 40ft Raptor. Gotta start building my database so when I buy the next truck I get what I need. My current truck is pretty awesome with the G56 and 3. 73's, but since I have the older model G56, I did upsize tires to 285/75's in order to get 2050rpms at 70mph.

 

[RVTRKN]

The 3:42 would have been a problem in the axle only. You can always down shift to make the proper engine speed but the strain on the axle is a lot greater than a higher ratio. You made the write decision with the 3:73. Both of mine have the 3:73's and they both pull heavy just fine, but when my C&C is pulling close to the max GCWR, (DMV registered 26K) I run it a lot in 5th when going up slight grades and 4th pulling steep grades. I think it has been a great choice so far, just this last week I had to pull my boat to Las Vegas and then to lake Mohave with the C&C because an illegal hit my 04. 5 and its getting repaired. The MPG is worse than my 04. 5, but it would have been more of a MPG loss than what I would of had with 4:10 or higher gears.



If you are only going to tow lite or haul lite loads it would be a good choice and even better MPG, but once you start hauling heavy, the cost of repairing the rear axle would surpass the savings of fuel.

 

[mikel]

Thats great, let us know how you like the new truck with 3. 73's and especially how it pulls. I like the idea of 3. 73's since I would use the truck for both driving empty, to towing a 20ft flat trailer with quads, to pulling my 40ft Raptor. Gotta start building my database so when I buy the next truck I get what I need. My current truck is pretty awesome with the G56 and 3. 73's, but since I have the older model G56, I did upsize tires to 285/75's in order to get 2050rpms at 70mph.

Hey, so far so good. I've just been driving around empty so far but with the 3. 73's I'm seeing about 1800 rpm at 70 mph on the freeway. I just got my hitch installed and will hopefully be pulling this weekend. I'll report back when I get some towing time.