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Thread: Truck Rear Ends

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    Truck Rear Ends

    Any Gearheads on here?
    Been looking at used trucks, Silverados or Sierras mostly. Been debating between 3.42 and 3.73 rear ends. I understand better milage with the 3.42, better towing and torque with the 3.73. Leaning toward the 3.73, but there are a lot more of the others available. Then there's 6-speed vs. 4 speed. So I'm wondering, does the 6 speed offset the 3.42 in terms of towing performance so it will not suffer compared to a 4 speed with the 3.73 gearing?

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    What engines are you looking at getting in it? Are those 4 and 6 speeds manuals or autos? What do you plan on towing?

    My powerstroke has 3.55 gears and a 5 speed manual. I was told the 6 speed manual would only give me a lower 1st gear. They are great when not towing or not towing a heavy load but when I get towing heavy loads it really has to big of a gap between the gears and I wish I had 4.10's or a spliter on it. Still I hate to give up the 19mpg I get with the 3.55 gears when not towing. I think 3.73 would be a good compromise.
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    Really depend on the loads you are towing. I had a Ford diesel with 3.55s that did fine with less than 8000#. Bought a new 28' boat that came in at 11.5K on the trailer. It really turned into a slug and I had a hard time getting it up a launch ramp sometimes. Changed the gears to 4.10 and it pulled great....but the mileage sucked.

    One thing to remember, diesels have a very narrow torque/power range. The "sweet spot" on my Powerstroke is about 1950 rpm. The truck mfrs are doing a better job in their transmission offerings. More mid range gearing allow you to keep the rpms where they need to be when you are towing. Generally speaking, the heavier the load, the lower gearing is better. MM is right about the splitters. I had a Gear Vendors splitter on my old Ford, which gave me 6 gears forward on the C6 auto trans. With the 4.10 rear end, I chose over gearing, which gave me better mileage. I could have under gearing which would have gave me lots more "pulling" ability, but a lot less mileage. My current Powerstroke 7.3 has 3.73s which Ford does not offer today. It is a great choice for me now as I am only towing a 10,000# travel trailer. I get the best performance and mileage.

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    Thanks for the replies.

    I'm looking at Chevy/GMC 1500s with a 5.3 in them, automatic transmission, not a diesel. Heaviest towing would be a mid-to-larger size travel trailer, I'm guessing at least 5000 but no more than 7500 pounds (currently pull a pop-up with an old Cherokee, and we'd like to upgrade he camper in the near future, so might as well upgrade the tow vehicle now). With the 6 speed, you should, in theory, spend more time in the power band, and would that offset some of what you would loose in terms of torque going from a 3.73 to a 3.42 (basically, I've run across some good deals on used trucks with 3.42's, I had been leaning toward the 3.73, I do a fair amount of highway driving, so I'd probably actually see a small benefit in mpg, but I don't want to sacrifice too much). I think most of the newer GMs come with a tow/haul mode, which keeps you in a lower gear for a longer period as well.

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    Quote Originally Posted by Murdy View Post
    Thanks for the replies.

    I'm looking at Chevy/GMC 1500s with a 5.3 in them, automatic transmission, not a diesel. Heaviest towing would be a mid-to-larger size travel trailer, I'm guessing at least 5000 but no more than 7500 pounds (currently pull a pop-up with an old Cherokee, and we'd like to upgrade he camper in the near future, so might as well upgrade the tow vehicle now). With the 6 speed, you should, in theory, spend more time in the power band, and would that offset some of what you would loose in terms of torque going from a 3.73 to a 3.42 (basically, I've run across some good deals on used trucks with 3.42's, I had been leaning toward the 3.73, I do a fair amount of highway driving, so I'd probably actually see a small benefit in mpg, but I don't want to sacrifice too much). I think most of the newer GMs come with a tow/haul mode, which keeps you in a lower gear for a longer period as well.
    Get the 3:73, or a 4:11. If you add larger tires/wheels, or the truck already has them, that will reduce your overall effective gear ratio. I had a friend, who put over 200,000 on his Chevy with a 5.3 L engine, with 4:11 gears, and a good bit of that was towing horse trailers. That being said, if the truck is not 4WD, it is relatively inexpensive to change the gear ratio.
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    With the 5.3 I would get the 3.73's. They aren't monsters of power like diesels can be so if you do some towing and it isn;t your commuter car, you cant go wrong with the 3.73's. I think the difference in mpg is negligible

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    Towing with the smaller gas engine I think the lower gears would be the better choice but I am not at all familiar with that 6 speed auto and with it the higher 3.42 gears might work just as well?

    Proper gearing will compensate for lack of power and lots of power will compensate for lack of proper gearing.
    Last edited by Musket Man; 08-01-2014 at 08:13 PM.
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    Like the others said, go with the 3.73 you will be happy.

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    Thanks, all -- been outa the loop the last 2 days. I appreciate the input. Seems like if you go newer than 2009, the 3.73's start becoming real hard to find -- which one salesman claimed was due to the 6-speed tranny. I was looking at one over the weekend that had a tow package, and I called to talk to the dealership. They told me it had a 3.08. Surprised me that that was available with a tow package. I wouldn't touch it myself. I'm still looking, but on further research, I wouldn't consider the 3.42 with the 6-speed a deal-breaker at the level I intend to tow at.

 

 

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