5.9 vs 6.7, auto vs manual for towing 20k th

[Ben feral]

I've got a 2003 5.9 dually Auto but I'm using to pull my 20,000 lb toy hauler. It does okay in terms of power though it certainly leaves something to be desired, but the big issue is braking. It'll be damn nice to have an engine brake, or even just the ability to reliably brake with the transmission.
A buddy has a 2008 6.7 l which of course already has an engine brake, but it's a single rear wheel, it's got a tuner in it but I'm not entirely sure I trust, it has a bunch of wiring issues including what I believe to be a ****ty plug on the transmission, and consequently it's having transmission issues. I'm pretty sure the issues are purely electrical. I can pick up his truck for $6,700 bucks, and I can sell my 5.9 for more than that, but I'd have to swap my front and rear axles as I need the dually for the towing capacity, and while I do like that he's got a mega cab, the rockers are blown out. I can fix that as well. I like my interior better as I've got power seats, but Minor details
The big question though, is what I'd be better off sticking with my 5.9, bumping the power, and either beefing up the auto or dropping in an NV 5600, or would it be better to just start with the 6.7 and 68 rfe? If I stick with the 5.9, I have to do an engine brake and possibly transmission. I could get away with just the engine brake, cuz I am making enough power to get me where I need to go, but it's anxiety inducing trying to accelerate, and 12% 20 mi long grades are a little terrifying especially considering I don't have a transmission temperature gauge.

What says the internet. I feel like the bone stock 6.7 with its stock brake and bigger transmission is really starting with an upgrade, but I don't have a heap of time to be swapping axles, and troubleshooting what is hopefully only transmission electrical issues. The other consideration here is that while everybody is trying to sell 2003 duallys with a blown up transmission or motor for near 20 grand, even if I posted it at 7k I'd be surprised if I ever even got a call back. Everyone is asking absolutely outrageous prices for ****ed up vehicles, but I've got several perfectly good trucks listed for less than half the regular asking price cuz I'm not trying to Dick anyone, and I haven't got a single call on any of them. I live full time in my trailer on the road, so I really don't want to have yet another truck added to the fleet that I have to leave in storage. Is the 6.7 really worth the upgrade?

 

[Ozymandias]

Drop a Pacbrake with controller in yours and a Trans temp gauge and enjoy.
I'd also put an upgraded valve body in or at least a Trans-Go shift kit.
The 48RE is very capable with just minor help and easy to maintain.

 

[Ben feral]

Drop a Pacbrake with controller in yours and a Trans temp gauge and enjoy.
I'd also put an upgraded valve body in or at least a Trans-Go shift kit.
The 48RE is very capable with just minor help and easy to maintain.

Dropping in a brake and valvebody into my 5.9 is easy, but man, i've heard nothing but bad things about the 48re and more than 50 extra ponies. I really can't afford to be blown up.
Also, can't find the TG valvebody right now. They almost seem like they're outta business .
How far can the stock 48re internals really safely get me with near 300k on the odo?

 

[Ozymandias]

300k says nothing, it's all about how it was treated through its lifetime, there is no such thing as a fixed milage where it needs a rebuild. Use and abuse you know.
The 48RE can be upgraded to any power level that Cummins can deliver - but it comes with a price tag - but that applies to the 68RFE as well.

Running these trannys for 20 years now and they have never let me down, and so simple built that you could do a rebuild on a Walmart parking lot. I just love the simple technology of the 60's.

 

[cerberusiam]

Pulling a 20k toy hauler with an 8k truck, you are out of bounds on braking and hauling capacity, by a lot!

At 300k you are due for a rebuild on a stock 48RE, even at stock power and that weight for very long. Even with a HD tow rebuild the 2003 48RE won't live using an EB without some additional items and they are no longer available. The only good choice at that time is a constant pressure VB like Firepunks Anteater or a reverse manual VB setup for some have hitting. The latter is a but clunky as OD and lockup is manual but with a good tight TC and some tuning it isn't bad. If you want to use it for multi-drivers then it is not a good idea. A constant pressure VB would be much better retain auto functions for lockup and OD.

It will cost about 1/2 again as much to beef a 68RFE to level you need, they just have more gears and more problems while not being heavier duty. A 351VE turbo on a 68RFE truck is not that impressive and a whole lot more expensive to build up. A manual truck would be a better choice but that can be a can of worms also. Trying to find a NV5600 to rebuild is bordering on impossible, Super Stick has a waiting list of people needing a core for them to rebuild. A worn NV5600 is a PIA when you get enough clutch into to hold and setting them up correctly is an art that few have.

A G56 is easier to find but heavy towing with them can also be a problem without adding braces, coolers, and probably some other parts. Good thing is if you have the coin Super Stick has a lot of billet gears for them in stock.

Really, you need a 4500 or 5500 to do what you are doing with heavy enough parts to last a good while. A more expensive choice but a more effective one in the long run.

 

[Rowdy Dalton]

I second the 4500 or 5500 . Sell both trucks, and get a used 4500 with lower miles.

 

[AH64ID]

Not to get too deep into the truck size ball of worms, but to answer your question of the 6.7 being worth the upgrade… yes, period.

I towed with my 05 5.9 that was modded very well for towing. BBi Stage 1 injectors, Colt Cam, Garrett Turbo, QSB Pistons (03/04 style), intake mods and custom tuning. I ran both a Jacobs exhaust brake and then a Pac PRXB, both had their advantages but the PRXB was the better brake. With the NV5600 is was a great towing setup, power for days and ran cool towing around the mountains. I also did some suspension mods that really improved its stability with a trailer. Truck was making ~480/1000 at the crank.

My bone stock Aisin/6.7/3.42 truck did better, not only the power but also the way the truck handled the weight. The 18 was rated for 385/930. The 05 had more pull from 2500-3000 rpms, but I was rarely ever there. From idle-1800 the 6.7 really out-pulled the 05, effortlessly. 1800-2500 they were pretty similar, the 6.7 was just quieter and smoother. The 13+ frame/suspension handles heavy weight much better than the 03-12 frame/suspension.

Now with a Aisin/6.7/3.73 truck rated at 420/1075 it’s another step up in towing power. The advantage of the 05 is probably down to 2800-3000 rpms, where I rarely am aside from exhaust brake use.

I do miss the 05, and the manual transmission, but the 6.7/Aisin combo is worth the upgrade.

SRW weren’t rated to tow 20K trailers until 2019.

3rd gen 5.9’s had the same GCWR for SRW and DRW, neither of which were high enough for a 20K trailer. There was a slight improvement for 6.7, but nothing notable until the frame redesign in 2013. Yes people did/do exceed those ratings on the 03-12 trucks often, but the trucks weren’t rated for it. Think I had my 05 SRW as high as 26 or 27K a couple times.

My 0.02 is to stick with a DRW, with a 6.7/Aisin/4.10 combo being the best. The Aisin didn’t get mated to the P/U until 2013, but was available in the C&C prior. Nothing wrong with a C&C for your application, but a Aisin DRW pickup would also do fine.

 

[Rowdy Dalton]

Not to get too deep into the truck size ball of worms, but to answer your question of the 6.7 being worth the upgrade… yes, period.

I towed with my 05 5.9 that was modded very well for towing. BBi Stage 1 injectors, Colt Cam, Garrett Turbo, QSB Pistons (03/04 style), intake mods and custom tuning. I ran both a Jacobs exhaust brake and then a Pac PRXB, both had their advantages but the PRXB was the better brake. With the NV5600 is was a great towing setup, power for days and ran cool towing around the mountains. I also did some suspension mods that really improved its stability with a trailer. Truck was making ~480/1000 at the crank.

My bone stock Aisin/6.7/3.42 truck did better, not only the power but also the way the truck handled the weight. The 18 was rated for 385/930. The 05 had more pull from 2500-3000 rpms, but I was rarely ever there. From idle-1800 the 6.7 really out-pulled the 05, effortlessly. 1800-2500 they were pretty similar, the 6.7 was just quieter and smoother. The 13+ frame/suspension handles heavy weight much better than the 03-12 frame/suspension.

Now with a Aisin/6.7/3.73 truck rated at 420/1075 it’s another step up in towing power. The advantage of the 05 is probably down to 2800-3000 rpms, where I rarely am aside from exhaust brake use.

I do miss the 05, and the manual transmission, but the 6.7/Aisin combo is worth the upgrade.

SRW weren’t rated to tow 20K trailers until 2019.

3rd gen 5.9’s had the same GCWR for SRW and DRW, neither of which were high enough for a 20K trailer. There was a slight improvement for 6.7, but nothing notable until the frame redesign in 2013. Yes people did/do exceed those ratings on the 03-12 trucks often, but the trucks weren’t rated for it. Think I had my 05 SRW as high as 26 or 27K a couple times.

My 0.02 is to stick with a DRW, with a 6.7/Aisin/4.10 combo being the best. The Aisin didn’t get mated to the P/U until 2013, but was available in the C&C prior. Nothing wrong with a C&C for your application, but a Aisin DRW pickup would also do fine.

Good write-up.

 

[slowmover]

“I live full time in my trailer on the road, so I really don't want to have yet another truck added to the fleet that I have to leave in storage. Is the 6.7 really worth the upgrade?”


Full time, but with a home/shop somewhere?

Genuine full time in that no property, but that which is rented, I concur with the 4500 idea.

Where the truck is storage for tools, etc, and the trailer is heavy, don’t skimp on on the TV. Dump the rental expense “back home” by disposing of the boat anchors from the past.

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[Ben feral]

Full time as in I'm legally homeless .
Bit of a backstory I won't get into, but I'm full time on the road and it's killer. I run several companies from my trailer, I typically spend a week or so at a given hot-spring and then move to the next one. There is nowhere to go home to.

So I ended up grabbing a buddies 08 6.7 6spd megacab, and while it's not without some horrendous electrical issues, my GOD does it pull harder than the 5.9, and I can't believe I spent the last 18 months without an engine brake. Night and day difference.

Unfortunately, PO did some real ****y wiring, and the truck was recently at a trans shop to swap out a flex plate. They didn't unplug the trans before pulling it back, and destroyed all the connectors/harness, so there are several buggy electrical issues I gotta work out. REally hoping it's all electrical. When she goes, she goes. Intermittently get PRN8 on the dash, and/or limp 4th, but I KNOW the trans pigtail is dicked. Pulled up a mountain pass though that with the 5.9 I was struggling in 1st and often in 4L 1st up the grades, and with the 6.7 I never once had to come below 4th and lockup. I also used the brakes maybe twice momentarily during the entire 7.5h drive (all mountains). Crazy difference.

I'll definitely need to swap leafs out or add air bags. I took the 4.10 dually outta my 03 5.9 and put it in the 6.7, but couldn't get the bigger overload leafs outta the 5.9, so i'm just barely inverted with the trailer fully loaded to 19.5k lbs. Not ideal.

I kept looking at a 4500/5500, but honestly, same motors, just bigger axles/suspension, which I can beef up myself as time permits. I take it pretty easy on the rear axle as is, as it's got a slight whine to it and i Haven't had time to re-set the gear.

 

[AH64ID]

The frame is also very different on a C&C, even a 3500. It’s more than just the suspension/axles.

 

[Ozymandias]

Reset a pair of gears that is already worn in is a sure way to disaster.

 

[NIsaacs]

Reset a pair of gears that is already worn in is a sure way to disaster.

I think he exchanged complete rear axles. SRW for the DRW.

Edit: Okay I see what you mean now, he did mention a gear reset. Yes, that's not an easy trick.

 

[NIsaacs]

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I'll definitely need to swap leafs out or add air bags. I took the 4.10 dually outta my 03 5.9 and put it in the 6.7, but couldn't get the bigger overload leafs outta the 5.9, so i'm just barely inverted with the trailer fully loaded to 19.5k lbs. Not ideal.

Do you have a flat bed or are you running the dually axle with the SRW bed, or did you change beds too?

Where do you find 20miles of 12% grades? An '08 6.7, even tuned, is not going to pull a 20k trailer up that in 4th.

I have a short 7% grade that I tow on regular, inside the city limits, so you can't take a run at it. With my '21 SO (3.73's), it works hard in 4th with 26-27k GCW.

 

[slowmover]

The frame is also very different on a C&C, even a 3500. It’s more than just the suspension/axles.

I advise the OP that this is so. IIRC, the wheel cut is tighter (this matters). Do some research.

The oilfield hotshot I did with similar 3500 ran reliably to 300k, but I don’t know who’d have bought them afterwards.

Short bed also ain’t your friend. In Texas or Massachusetts they’re called diesel Honda Ridgelines. (This is great fun on the CB to startle some Home Depot Daddy and get the other truckers to laughing). An 8’ bed is better by every measure. Zero downside.


I truly love the 5600 with my 555. Today, though, a 4+2 Auto gets the nod in most ways. The last Man’s Trans advantage is low-speed maneuvering & backing.

— It’s easier to hustle a Manual around in short spurts to use confined space even though the Auto will have been “faster” to top speed.

That backing ease thing may not seem important to many, but it’s an ancient joke (truism) among truck drivers that, they don’t pay us to drive them cross-country, they pay us to get them backed in.

The vast majority of “accidents” are in backing. A clutch makes transitions (momentum changes) easier to feather. IMO, that’s the deciding factor (comfort level).

“Grampa over there seems kinda slow getting that 36’ backed . . but you’ll notice he never really stops” (got it in “faster”). Auto Joe Sixpack was rockin’ the rig— herk & jerk the whole way”.

Joke aside, it’s not that one is “better”. They’re different. The Manual has three tools, the Auto only has two (left foot working the brakes, hard).

The sweetness of a Cummins is that it almost won’t stall. Makes 5600/56 easy to get a load underway and in backing.

The rider has to adjust himself to the horse. Just remember that Grampa Boomer over there can back a wagon with a four-horse hitch (ha!). Manual takes years to become good. Too many situations call for fairly complex decision-trees that mitigate it as first choice. (“Brakes-only”, is not a possibility with Manual in an emergency; plenty of wanna-be types never learn what’s needed, to their sorrow and ours).

Auto is default choice.

OTOH, my leaning towards Auto would go away if one could change the shift pattern that Reverse is atop First on the 5600. I’d never consider changing. That reach all the way across on OEM can be a PITA some times.

Good luck with how it goes!

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[CrewCabDiesel]

I did the swap from auto to nv5600 in a early 2004. Hardest part finding a good NV 5600 at a reasonable price. I have hated the 48re, in 2003-2004 can't program shift points to match heavily modified 5.9. Wiped out two automatics and I was afraid of frying the 3rd one. So I got the right parts put in my knee(another story and the reason I bought a automatic in the first place). Got lucky found almost complete nv5600 swap. Dropped in a South Bend dual disk clutch, a BD short throw shifter and I'm a happy camper rowing gears again.
My mpg went up 3mpg too. I also decided to add a Yukon free spin kit and now I have a 2wd low which is awesome for moving around heavy trailers, especially backing up. And please don't tell my wife how much I spent, she found the receipts from the engine build a few years ago and wanted to know how I could spend $11k on a old truck motor.

 

[Regcabguy]

300k says nothing, it's all about how it was treated through its lifetime, there is no such thing as a fixed milage where it needs a rebuild. Use and abuse you know.
The 48RE can be upgraded to any power level that Cummins can deliver - but it comes with a price tag - but that applies to the 68RFE as well.

Running these trannys for 20 years now and they have never let me down, and so simple built that you could do a rebuild on a Walmart parking lot. I just love the simple technology of the 60's.

I had a DTT w/Smart Controller and a PacBrake on my 98.5 2500. That was the only way I felt safe on the freeway with my 2200# camper load. 24v auto Dana 70's brakes sucked.

 

[Rowdy Dalton]

I had a DTT w/Smart Controller and a PacBrake on my 98.5 2500. That was the only way I felt safe on the freeway with my 2200# camper load. 24v auto Dana 70's brakes sucked.

2200#?? That's kind of light. Do you mean 22,000 lbs?

.

 

[CJ8Rockcrawler]

2200#?? That's kind of light. Do you mean 22,000 lbs?

.

I believe he's speaking of a slide in camper.

 

[Tuesdak]

I've got a 2003 5.9 dually Auto but I'm using to pull my 20,000 lb toy hauler. It does okay in terms of power though it certainly leaves something to be desired, but the big issue is braking. It'll be damn nice to have an engine brake, or even just the ability to reliably brake with the transmission.

As recommended to go to a Medium Duty 4500 5500 or other newer and capable tow vehicle because the 2003/2008 isn't the proper tool for the job. I suggest checking insurance rates before making a purchase of a 4500/5500 vs. a newer 3500 DRW that's rated for your RV/home on wheels.

You already notice the difference with the more capable 2008 6.7. However it's a project and still not what you need to haul the RV weight around without gross negligence applying esp. if you wreck. I walk back this comment IF one of your businesses is an "Upfitter" and you are changing the sticker on the door for the vehicle's weight capabilities by doing things like adding DRW. Not may left that will take on the liability for applying this sticker. We can argue all day about everything else being "the same" between a SRW and a DRW, however, unless you can change the door sticker by adding a sticker from an upfitter the numbers stay "the same" SRW rating as it left the factory.

I didn't say the accident was your fault. I said it's your Gross Negligence because that overloaded rig should not have been on the road without an upgraded sticker.

Just like "Great Smoke Stories" helped bring extreme emissions controls to our diesel engines and enforcement action putting aftermarket outfits out of business... Just Saying! Try and not set a bad example. If your rig is not capable it is a better idea to hire a transport company, including say a local towing company, to move your RV. By the time you are done with time/labor/parts it may be cheaper than owning and storing a bunch of project trucks.