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First tow 3.21 review

Redfour5

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This quick and dirty will expand when I get home. I have a 21 Built to Serve 5.7 with 8000 tow capability and 1300 payload. My trailer is 27.3 feet long 5700 lb, 600 lb tongue (dry). I'm 6800 and 810lbs loaded and right at payload running. I went from Helena MT to Spokane WA, 310 miles, two moderate passes.

First impressions. I was running at 72 mph and less on the passes regular traffic, on 10 mile 35/45 mph construction zone. I had 1300 miles on the odometer at start.

First impressions: Mileage 8 mpg calculated 8.6 by lyometer. Plenty of power exceeding expectations even up passes. Not as much as my old 3.92 2015 Outdoorsman and delivers it differently as you can tell the tranny is doing some of the work vs a 3.92. It spent a lot of time in 5th gear some in 6th and a little in 7th. Never saw 8th. Tow haul. Mileage about the same as the 3.92. The biggest weakness was the Falkens too soft (sense of wallowing vs KO2's at 50 psi old truck) even at 41psi temps at 95 to 100 degrees the whole trip. Most important. Plenty of power.
 

LaxDfns15

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So if you put the truck in tow/haul mode it will lock out of 8th. That's why you only ever hit 7th.

EDIT: As seen below I was wrong.
 
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Rlaf75

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So you're saying that it did fine? My trailer is an older beefy 7x11 enclosed and it's pretty heavy empty and gets really heavy with 2 big Harley Davidson's and a bunch of other equipment in it. I'm a little nervous about my 21 BTS with 3.21 gears when it comes time to tow my trailer. I liked the truck so much I didnt pay too much attention to which gears it had. If I ordered the truck I would've got the 3.92's but this was a lot purchase. I'm pretty sure I'll be fine after I actually hook the trailer up
 

Trooper4

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So you're saying that it did fine? My trailer is an older beefy 7x11 enclosed and it's pretty heavy empty and gets really heavy with 2 big Harley Davidson's and a bunch of other equipment in it. I'm a little nervous about my 21 BTS with 3.21 gears when it comes time to tow my trailer. I liked the truck so much I didnt pay too much attention to which gears it had. If I ordered the truck I would've got the 3.92's but this was a lot purchase. I'm pretty sure I'll be fine after I actually hook the trailer up
Someone had a thread about the difference between the two, and it was something like one gear higher than the 3.92.
 

Redfour5

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So you're saying that it did fine? My trailer is an older beefy 7x11 enclosed and it's pretty heavy empty and gets really heavy with 2 big Harley Davidson's and a bunch of other equipment in it. I'm a little nervous about my 21 BTS with 3.21 gears when it comes time to tow my trailer. I liked the truck so much I didnt pay too much attention to which gears it had. If I ordered the truck I would've got the 3.92's but this was a lot purchase. I'm pretty sure I'll be fine after I actually hook the trailer up
You only have 8K lbs total. I'm around 1300 lbs below that consciously. AND I'm right at my 1300 lb payload. Since it is a work trailer, you may be OK. If it is a two axle it likely has two 3500 lb axles. Unless the trailer is way over weight you are likely OK. If it is a single axle, i might be worried about the trailer.
 

Rlaf75

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You only have 8K lbs total. I'm around 1300 lbs below that consciously. AND I'm right at my 1300 lb payload. Since it is a work trailer, you may be OK. If it is a two axle it likely has two 3500 lb axles. Unless the trailer is way over weight you are likely OK. If it is a single axle, i might be worried about the trailer.
Yeah I'm not worried about the trailer. It's been loaded several times over the course of the 20 years I've owned. My main concern it the 3.21 hearing in the truck pulling it. I'm not even concerned about miles per gallon at all either
 

silver billet

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Yeah I'm not worried about the trailer. It's been loaded several times over the course of the 20 years I've owned. My main concern it the 3.21 hearing in the truck pulling it. I'm not even concerned about miles per gallon at all either

The concern about gear ratio is pretty irrelevant these days with 8 and 10 speeds. The only spot you'll notice it is <= 2nd gear. On the highway towing, there is no difference; a 3.21 and 3.92 towing the same load at the same speed will be at the same RPMs with the same power/MPG, except the 3.21 will be in one numerically lower gear than the 3.92 (it's just the name of the gear that is different, the actual mechanical advantage of gearing is pretty much equivalent between the two beyond 2n'd, and then finally the 3.21 gets an additional "top end" final gear.).

You know how all the youtube "reviewers" and Tundra fanboys like to talk up how good the Tundra is for towing? Well the 3.21 with the 8 speed has a lower first gear than the Tundra 6 speed with 4.30 rear end. The 3.21 also has a higher top gear than the tundra for unloaded cruising on the freeway. So the 3.21 kicks the Tundra's butt in both towing power and unloaded fuel efficiency, even with a much much lower rear end.

If you're one of these guys who lives in an RV and is constantly on the move every week and towing heavy, well the 3.92 would be a better option (just for easier pulls from a dead stop). If you're just pulling a trailer on vacation couple times a year, the 3.21 is a no brainer.

So don't worry about the 3.21, it's a great truck.
 

IvoryHemi

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Yeah I'm not worried about the trailer. It's been loaded several times over the course of the 20 years I've owned. My main concern it the 3.21 hearing in the truck pulling it. I'm not even concerned about miles per gallon at all either

When towing heavy you essentially get 6 useable gears with 3.21 and 7 useable gears with 3.92

I wouldn’t worry too much about it, you’ll have plenty of power
 

AMS Guru

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That's not true. Tow/haul affects shift points and lockup. It doesn't lockout 8th gear.
View attachment 103053
I do wish RAM would provide more "drive modes" to the truck for engine/transmission behavior other than the Tow/Haul mode. It would also be nice to control the exhaust brake on the EcoDiesel as well. The ZF tranny I believe is a solid quality unit and smooth but it doesn't like to stay in overdrive very well when the torque of the engine could/should be able to carry the truck. I went with the 3.92 this time around vs. the 3.21 after a lengthy test drive and hoping in my mixed driving I'll get similar or possibly even better mileage. Time will tell I guess. I would REALLY like to see RAM offer the 3.55 axle in more applications. It would be a great compromize I think......
 

millerbjm

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This quick and dirty will expand when I get home. I have a 21 Built to Serve 5.7 with 8000 tow capability and 1300 payload. My trailer is 27.3 feet long 5700 lb, 600 lb tongue (dry). I'm 6800 and 810lbs loaded and right at payload running. I went from Helena MT to Spokane WA, 310 miles, two moderate passes.

First impressions. I was running at 72 mph and less on the passes regular traffic, on 10 mile 35/45 mph construction zone. I had 1300 miles on the odometer at start.

First impressions: Mileage 8 mpg calculated 8.6 by lyometer. Plenty of power exceeding expectations even up passes. Not as much as my old 3.92 2015 Outdoorsman and delivers it differently as you can tell the tranny is doing some of the work vs a 3.92. It spent a lot of time in 5th gear some in 6th and a little in 7th. Never saw 8th. Tow haul. Mileage about the same as the 3.92. The biggest weakness was the Falkens too soft (sense of wallowing vs KO2's at 50 psi old truck) even at 41psi temps at 95 to 100 degrees the whole trip. Most important. Plenty of power.
Did you follow the manual break-in suggestions for towing? Not judging just curious - I started towing a small travel trailer (approx 3,200lbs loaded) at about 2,000 miles on the odometer and tried to follow the procedure and stay under 50mph for the first 500 miles towing but it is really tough to stay that slow on the interstate!
CAUTION:
  • Do not tow a trailer at all during the first 500 miles (805 km) the new vehicle is driven. The engine, axle or other parts could be damaged.
  • Then, during the first 500 miles (805 km) that a trailer is towed, do not drive over 50 mph (80 km/h) and do not make starts at full throttle. This helps the engine and other parts of the vehicle wear in at the heavier loads.
 

Rlaf75

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When towing heavy you essentially get 6 useable gears with 3.21 and 7 useable gears with 3.92

I wouldn’t worry too much about it, you’ll have plenty of power
The concern about gear ratio is pretty irrelevant these days with 8 and 10 speeds. The only spot you'll notice it is <= 2nd gear. On the highway towing, there is no difference; a 3.21 and 3.92 towing the same load at the same speed will be at the same RPMs with the same power/MPG, except the 3.21 will be in one numerically lower gear than the 3.92 (it's just the name of the gear that is different, the actual mechanical advantage of gearing is pretty much equivalent between the two beyond 2n'd, and then finally the 3.21 gets an additional "top end" final gear.).

You know how all the youtube "reviewers" and Tundra fanboys like to talk up how good the Tundra is for towing? Well the 3.21 with the 8 speed has a lower first gear than the Tundra 6 speed with 4.30 rear end. The 3.21 also has a higher top gear than the tundra for unloaded cruising on the freeway. So the 3.21 kicks the Tundra's butt in both towing power and unloaded fuel efficiency, even with a much much lower rear end.

If you're one of these guys who lives in an RV and is constantly on the move every week and towing heavy, well the 3.92 would be a better option (just for easier pulls from a dead stop). If you're just pulling a trailer on vacation couple times a year, the 3.21 is a no brainer.

So don't worry about the 3.21, it's a great truck.
Thanks guys. Yeah I'm not regularly pulling the trailer and I used to pull it loaded with furniture in Nissan Xterra with a V6 ad it did ok. I guess I'm just thinking old school gear head days when the lower gears had a lower end torque but I'm new to this 8 speed trans. My 5 speed Ram bighorn with the hemi had 3.55 gears and I liked the way it pulled the trailer. I'm sure I'm just over thinking the 3.21's.
 

Redfour5

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Did you follow the manual break-in suggestions for towing? Not judging just curious - I started towing a small travel trailer (approx 3,200lbs loaded) at about 2,000 miles on the odometer and tried to follow the procedure and stay under 50mph for the first 500 miles towing but it is really tough to stay that slow on the interstate!
CAUTION:
  • Do not tow a trailer at all during the first 500 miles (805 km) the new vehicle is driven. The engine, axle or other parts could be damaged.
  • Then, during the first 500 miles (805 km) that a trailer is towed, do not drive over 50 mph (80 km/h) and do not make starts at full throttle. This helps the engine and other parts of the vehicle wear in at the heavier loads.
Yep did the break in the trip started at 1300 miles. I averaged 8 mpg 768 miles.
 

Redfour5

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Yeah I'm not worried about the trailer. It's been loaded several times over the course of the 20 years I've owned. My main concern it the 3.21 hearing in the truck pulling it. I'm not even concerned about miles per gallon at all either
I was pleasantly surprised. Yes, the 3.21 works...differently and a bit harder. You can tell the tranny is more involved but power wasn't really a problem.
 

Redfour5

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The concern about gear ratio is pretty irrelevant these days with 8 and 10 speeds. The only spot you'll notice it is <= 2nd gear. On the highway towing, there is no difference; a 3.21 and 3.92 towing the same load at the same speed will be at the same RPMs with the same power/MPG, except the 3.21 will be in one numerically lower gear than the 3.92 (it's just the name of the gear that is different, the actual mechanical advantage of gearing is pretty much equivalent between the two beyond 2n'd, and then finally the 3.21 gets an additional "top end" final gear.).

You know how all the youtube "reviewers" and Tundra fanboys like to talk up how good the Tundra is for towing? Well the 3.21 with the 8 speed has a lower first gear than the Tundra 6 speed with 4.30 rear end. The 3.21 also has a higher top gear than the tundra for unloaded cruising on the freeway. So the 3.21 kicks the Tundra's butt in both towing power and unloaded fuel efficiency, even with a much much lower rear end.

If you're one of these guys who lives in an RV and is constantly on the move every week and towing heavy, well the 3.92 would be a better option (just for easier pulls from a dead stop). If you're just pulling a trailer on vacation couple times a year, the 3.21 is a no brainer.

So don't worry about the 3.21, it's a great truck.
Yep, that pretty much describe my experience.
 

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