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Old 10-31-2013, 11:40 PM   #41
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Ok...I from Arkansas. I talk slow, understand nothing and skip stuff when I read....so if I got anything correct then there are a few factors for fuel consumption basics. Friction:tires and weight maybe. Wind resistance: faster is more. Torque:horse power to weight/gear ratio. Somehow this math has to work for your hp/weight/fuel use.

Is this even close?
sounds good to me.
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Old 10-31-2013, 11:43 PM   #42
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JFM-jr:

As I have repeatedly stated, I am taking issue with an earlier claim that a lower gear ratio requires a higher engine rpm to maintain a given speed. I agree with you that a gear ratio of “4.56 will need alot more [engine] revolutions to maintain 60mph than a 3.73 will..” Therefore, is the converse not also true, i.e., that a gear ratio of 3.73 will need a lot fewer engine revolutions to maintain 60 mph than a 4.56 will? If so, that contradicts the earlier claim I am addressing.

Of course the wheels/axles rotate at the same rate to maintain 60 mph regardless of the gear ratio. What I have been arguing is that, with a lowered gear ratio, the engine rpm must be lowered (not increased) to maintain that speed, all other factors being equal. Are you in agreement? If so, then you are, like me, in disagreement with the earlier claim.

Not to belabor the point, but what is faulty about my understanding that, if the gear ratio is increased to 4.56, then for a given engine>transmission>pinion rpm the ring-gear>>wheels will make fewer revolutions than with a 3.73 gear ratio? I am not ignorant of the fact that the engine>transmission>pinion rpm varies as a function of how far the gas pedal is depressed. I am just wondering what you think is wrong with my understanding of the relationship I as presented it.
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Old 11-01-2013, 12:14 AM   #43
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Your understanding is wrong because it is wrong. Simply put, a higher ratio rear axle ratio requires a higher engine speed to maintain the SAME SPEED down the road. That is a fact whether you understand it or not.

If your truck runs 3000 rpm with a 3.42 axle ratio at 60 mph, it will run at 3271rpm with the 3.73 gears.

Higher numerical gear ratios will require higher engine rpm at the same speed.

The higher ratios may result in reduced stress on the power train, but it depends on other variable, such as torque curves and transmissions shift points.

THESE ARE FACTS NOT OPINIONS.
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Old 11-01-2013, 07:16 AM   #44
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more than twice as much, that front diff is a whole lot more involved than the rear. on say a K-5 or more current IFS the front labor is quite a bit more than the rear.
Post # 21 covered that! Youroo!!
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Old 11-01-2013, 10:05 AM   #45
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Nothing wrong with that, I try to tow in a place that suits the current gear selection. There is a window for each gear, I don't like to sit on the fence of at say 55. When 5 mph more or less is easier on the system. I say system because I am a transmission guy I watch my trans temp closely. You need for the converter to be locked for the trans to cool down. ( when a trans goes into hot mode it applies the TCC. To help it cool down)Whatever makes it stable is what I do. The new diesel I have has much much wider windows of operation. And that is simply because of more torque. The Allison transmission is a beast compared to what I was using. The rear axle and brakes are much more stout as well. Happy truck = happy trip.
I watch my tach, and I believe I can tell when my torque converter is locked, since you are a transmission guy is this not possible?
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Old 11-01-2013, 10:15 AM   #46
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Wilem - is there a way to force the tranny to lock the torque converter? My expertise is manual transmissions, so I'm curious if a switch or ??? could be added. Also, where is a good place to learn about transmissions/drivetrains?
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Old 11-01-2013, 11:27 AM   #47
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Converter operation and the mechanics inside it is a really neat thing to learn about.
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Old 11-01-2013, 12:11 PM   #48
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Not sure on other makes and models, but the Super Duty Fords from 2011 on have a new 6 speed (same tranny gas or diesel) and the lockup is very pronunced and you can see it on the tach. Because there is a gear indicator you know if it was a gear shift or lockup and they lockup quite early especially in T/H or full manual mode. T/C lockup is a function of the factory programming of the tranny.
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Old 11-01-2013, 02:44 PM   #49
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Garbonz (assuming your post 43 was addressing me):

I agree with you that “higher numerical gear ratios will require higher engine rpm at the same speed.” Can you cite anything I have written that argues against that relationship?

If “higher numerical gear ratios will require higher engine rpm at the same speed,” then it follows that lower numerical gear ratios will require lower engine rpm at the same speed.

For the umpteenth time, I have been responding to an earlier post (number 7) that claimed “the lower your gear ratio, the greater the RPM's from your engine to maintain an equal driving speed. “ Am I correct in assuming we both agree that claim is not accurate, all other factors being equal?
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Old 11-01-2013, 03:10 PM   #50
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Garbonz (assuming your post 43 was addressing me):

I agree with you that “higher numerical gear ratios will require higher engine rpm at the same speed.” Can you cite anything I have written that argues against that relationship?

If “higher numerical gear ratios will require higher engine rpm at the same speed,” then it follows that lower numerical gear ratios will require lower engine rpm at the same speed.

For the umpteenth time, I have been responding to an earlier post (number 7) that claimed “the lower your gear ratio, the greater the RPM's from your engine to maintain an equal driving speed. “ Am I correct in assuming we both agree that claim is not accurate, all other factors being equal?

Your claim is inaccurate. A LOWER ratio is a higher numeric value. So, 3.73 gears are LOWER than 3.55 gears.
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