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How to Select Proper Truck Axle Ratios

broocksbroocks Posts: 1
edited February 28 in General
Can someone please enlighten me to the importance
of different axle ratios. I was told that the 3.42
was the best for a Z71 or 2 WD chevy that would
occaisonally be used for towing. What is the axle
ratio and why is a 3.42 better? Thanks for your
help.

Comments

  • hcombs0hcombs0 Posts: 22
    The axle ratio is the ratio of the number of revolutions of the input shaft of a differential to one revolution of the half-shafts coming out of it. In the 3.42 axle, for instance, the driveline will turn 3.42 times for every 1 turn of the wheels (assuming your traveling in a straight line).
    The gear ratio is important because it determines the amount of mechanical advantage your truck has when pulling itself and any payload/trailer. The lower (numerically higher) the ratio is, the easier it will be for your truck to pull a given load, provided other things (engine/tranny combination) remain the same.
    However, you can't get something for nothing, or else we'd all be driving trucks with 4.11 to 5.00 axle ratios! In getting more mechanical advantage, you give up mileage, since your engine will have to turn more rpms for a given road speed. For example, where a 3.08 axle truck might turn 1400-1500 rpm at 65 mph, a truck with a 3.73 or 4.11 will turn upwards of 2000 rpm.
    There's some background, but let's look at your situation. I'd say that the 3.42 should be fine for light towing situations (2-3 tons) on relatively flat terrain, providing good mileage at highway speeds, especially with GM's overdrive transmission. You could go with 3.73, which has even more mechanical advantage, but there's an attendant loss in mileage when not pulling that you probably wouldn't be happy with.
    Good luck.
  • cdeancdean Posts: 1,110
    this input is coming from lots of chevy experience and by knowing lots of people and fleets with different combinations of axles and engines.

    if you get a 2WD, get the 3.42. geared perfect for no-load, runs great, still has good power for pulling. will get low mileage (~11 or 12) when pulling, but good mileage when empty.

    if you get a 4x4, get nothing (numerically) less than the 3.73. the 3.42s and 3.08s are too tall for these heavier trucks, and the engine really strains compared to the 3.73. the 3.73 4x4 runs as effortless as the 2x4 with 3.42. i've heard some Z71 owners with 3.42's getting worse mileage than those with 3.73s. that means the engine is working harder.

    if you plan to tow regularly, you might get the 3.73 in the 2x4, for much better pulling performance and mileage, but otherwise the 3.42 gets better mileage and runs great.

    i wouldn't get any chevy with a 3.08. my experience is it is just too tall a gear, and the only way to ever get good mileage with it is to travel on long trips often, something i don't do.
  • RoclesRocles Posts: 985
    The 3.08 is for the guy who tows twice a year. The small-block 8 or six from Chevy works well with this ratio in the light-trucks. My Chevy trucks have the 3.42 for added strength and ease on the motor. Then again, I'm a roofer and we always have crap in the bed weighing us down.
    Don't let anyone talk you into a 3.73 or lower(higher numerically)for any truck that isn't 4x4 or a heavy tower. Heavy as in anything over one ton(2 thousand lbs).
    It's what you really need that should matter. Don't listen to any clown telling you need a super low ratio unless you really need it. Otherwise, you will be paying Texaco every 200 miles.
  • lwflwf Posts: 223
    Just to add to the confusion, you may want to ask yourself if you want a limited-slip rear end. Some manufacturers don't provide that with the 3.08. I'm pretty sure Ford doesn't, and I suspect the same is true for the GM pickups. On the other hand, if you do want it, that eliminates one of the choices.

    I couldn't do any towing when I test drove a sample of what I recently bought, of course, but I felt the 3.08 was adequate and got it. But I've had shorter axle ratios (bigger number) before and enough experience to believe I know what's good for me. If you have never been through this before and are going to make a decision based entirely on what someone else tells you, I'd say you would be taking a chance getting a 3.08 and your best bet would be the 3.42, which I guess is what you were going to do even if you hadn't started this topic. You won't have to ask anyone the next time you buy a truck. By that time you'll be as pig-headed regarding this topic as the rest of us.
  • akjbmwakjbmw Posts: 231
    broocks
    To bring the concept up close and personal, Borrow a multi-speed bicycle and try starting from a stop in the highest gear. Then do the same maneuver in the lowest gear. See how fast you can go in low gear and still keep your feet on the peddles, then see how high gear does. When YOU are the engine, it becomes more clear.
    Now review the above entries again. :-)
  • RoclesRocles Posts: 985
    akjbmw,

    My hats off to you for an excellant analogy!!
  • bonvecbonvec Posts: 11
    I will soon order a Ford f350 dually with the 5.4 engine. I'm in the masonry business and haul heavy materials frequently. My current truck has a 351 engine and first gear is a creeper gear a setup that I really like. My question is do I need to special order to get a similar setup or does this setup come standard.
  • stanfordstanford Posts: 606
    You do realize that the V10 costs ~$200 more and gets, if anything, better mileage... not to mention considerably better performance and towing capabilty in the heavier trucks... don't you?
  • BrutusBrutus Posts: 1,113
    I would definitely go with the V-10 on a dually. As Stanford mentioned, early reports are that the gas mileage isn't much better with the 5.4 in the Superduty, if at all.
  • bonvecbonvec Posts: 11
    Here are my reasons for selecting a 5.4 engine. 1. I am reluctant to purchase a engine in its first years of production. Will there be some bugs to be uncovered. 2. My present truck has over 180,ooo miles and is all original and this is with extremely hard use. I am told that the 5.4 is basically a new version of my old reliable 351. 3. I am suspicous of claims of good gas mileage ,I once owned a 460 engine that gulped gas.Also are two additional cylinders two more potential problems. 4.This is going to be a work truck my351 has enough power and with my creeper gear goes everywhere I need to go. I don't want to appear stubborn but simply want the most reliable truck not the fastest. I am still open to suggestion.Does anyone have any experience with this 5.4 and how long has Ford been producing it.
  • cdeancdean Posts: 1,110
    the 5.4 is NOTHING like the 351. totally new modular engine design. its only been out a couple of years, and theres no real way to tell reliability yet. the v10 has been in the E350 vans for a couple years now and I would say the bugs should be worked out.
  • BrutusBrutus Posts: 1,113
    I believe the 5.4L and the V-10 have been around about the same amount of time. They are actually made on the same line. The new Triton engine was designed with a V-10 in mind, so they share alot of parts. That's one of the reasons, the V-10 option only cost a couple hundred bucks more than the 5.4L. The 460 had to have it's own line since it shared very little in common with the other Ford V-8 engines.

    Like cdean mentioned, they have been using them in the big Econoline vans. Until they built the Superduty, they didn't have an engine compartment big enough to hold the V-10. It won't fit in the F-150.
  • bonvecbonvec Posts: 11
    Brutus, do you know if a 5.4 has a equal amount of power as the old 351. And since they are similar do you believe the v10 and v8 will be similar as far as maintenance and durability
  • BrutusBrutus Posts: 1,113
    No idea about the 5.4L compared to the 351. I just sold my 92 F-250HD 5.8L. I believe they are both considered versions of the 351. I never had a problem with mine. It had 86,000 miles. However, it does appear as if the Chevy 350 beat it in mpg. But like I said, no problems at all with my engine. Still, from everything I've heard, I would not consider the 5.4L over the V-10. I have yet to hear one person on this site, or any of the other sites I participate in, say that the V-10 gets significantly worse gas mileage than the 5.4L when it comes to the Superduty. I've actually heard the opposite from some people. It's a matter of weight. The Superduty is not a light truck. It appears the V-10 is more efficient at pushing that weight than the 5.4L. But once again, I have to say that my 5.8L never cost me a dime in maintenance. I can only hope the same of the V-10 I ordered.
  • cdeancdean Posts: 1,110
    ford built the 5.4 off the same modular basis that the 4.6 v8 was built off of. the 4.6 was in t-birds and cougars for a while before they started putting them in the trucks. the 5.4 is basically a bigger bore version of the 4.6, and the v10 is the same, add 2 more cylinders. mechanically, there is absolutely nothing to compare to the 351.
  • KCRam@EdmundsKCRam@Edmunds Mt. Arlington NJPosts: 3,495
    The dilemma right now is the announcement from Ford that they are punching up the power on the 5.4 in the _light_duty_ trucks - to 260/345. Very close to the V10's 275/410, and well above the 5.4's current 235/330. There has been NO announcement as to whether the upgraded 5.4 will see SuperDuty use, or if so, when.

    I would go along with the majority here and go with the V10 (if you're sold on gasoline) strictly because the Super Duty trucks weigh more than the old 1980-1997 chassis. If you notice, the GVWRs were raised substantially, but there wasn't much increase in payload compared to the older body. All DRW Fords are now at 11,200 GVWR, up from 10,000, but there's a lot less than a 1200 pound payload increase in the otherwise identical configuration.

    KCRam - Pickups/Wagons/Vans+Minivans Moderator

  • bonvecbonvec Posts: 11
    I want to thank everyone at this site for their advice , It sure has made me rethink my position on this v8.
This discussion has been closed.