2.62 gear ratio

ok I give up. Some of the things some of you are saying make's me wonder if the closest you ever got to a truck was standing on the shoulder pumping your fist trying to one to blows his horn. Sorry for the insult but you need to think about what you say. you say I'm wrong about torque and the tell me you have to beef your driveline to handle the extra torque, Think driver it matter's where you gear reduction is. we pulled the same loads in the 70's with a290 and 900 lbs ft of torque, but everyone had 4.11's, today we have 16 to 2000 lbs ft of torgue is the only reason you ever heard of 2.62.

 

Had an 84 with small sit in sleeper . love that old truck, wasn't that old then. this 05 squeeks and rattles with only 600k, but it ride better.

 

It matters where the reduction is only if you're stressing the driveline. Most operations would work just fine with 2.62s and a direct 10 speed.

What transmission ratios did you have in the 70's? Don't know? Then why bring it up?

Funny you mention 2000 ft lbs engines and 2.62's. Try speccing that, it wont happen. Most directs can only handle 1650.

 

Well, first I will say that I know much less than you guys do, but I have always been interested in this topic.

So much of this has to depend on where you run, how heavy, mountains, length of haul, etc. Add on to that computer models, dealer spec'ing, optimum cruising rpm, tire sizes, aerodynamics, rolling resistance, hp/torque/ powerband, trans ratios... it's not hard to see confusion with so many variables.

What I do know is that if you have a small engine, say 300 hp, the higher that it is geared, the more it feels sluggish. The lower that it is geared (higher numerically), the more pep in your step so to speak.

So on a 600 hp engine, I would think the same fundamental rule still applies, to what extent I do not know. I will say that the guys that I knew that bought trucks geared higher than their old truck said their trucks were more sluggish pulling hills (no scientific data here).

My understanding is that overdrive is for cruising and direct is for pulling. My (limited) research on overdrive vs. direct is that theoretically direct should give better mpg, but in reality it very well could be negligible.

Also, for a new truck purchase, i would not necessarily follow what the fleets do, unless I actually ran one of their trucks myself. They will do anything to save a penny per mile (as they need to). They are not nearly as concerned with sluggishness/ driveline/ clutch issues/ longevity as an owner operator will be. If they decide they do not like it, they will just buy a new fleet geared differently. An owner operator does not have that luxury, and changing your gearing after the fact is an expensive proposition.

Again, I am sure you guys know way more than I do about this, especially when it comes to very high gearing and mpg, so take my .02 with a grain of salt.

Happy holidays to all, and be safe.

 

ok, I didn't mean to turn this into a knock down drag out. I apologize for that. your last post you said 2.62's will work for MOST operations. If what you've been telling me was true they would work for every operation. One of you said you have spec your driveline heaver because of the extra torque to turn 2.62's. Think about that for a sec, if it was 3.70's it would take less torque, meaning it's not as hard to move, so, if you put the same torque on the 3.70 it would be moveing faster, therefore smoking your 2.62's up a hill. 2000 ft lb on 2.62's, ask yourself why you can't get them. As for the transmission ratio slur, I ask for that, although you missed the whole point, the point being we didn't have enough torque back then to pull tall gears. Not knowing what ratios they were back then, yes I know, but it don't matter. we did have 10 direct's 1 to 1, 12513 .89, 15 over .79, first 18 I saw was .84, first 15 sp were called 10 sp with deep reduction and the deep reduction switch was on the dash. Had a 6 sp had to go through second gear to get to first gear and a 4 sp that you had to go into first gear hold a button down and pull into reverse. I don't mean this as a cutdown. but you've never pulled in some of the place's I'm talking about, I know this because if you had, we wouldn't be having this conversation. Ya'll have fun on your run, and if you pass close to Louisiana put it on here and i'll buy you supper.

 

You're not really making sense here. You put the same transmission and engine with the 3.70s in the same gear you would be going slower (road speed). Adjust your gear to match the engine rpm and road speed and guess what, you have exactly the same overall multiplication. The engine and axles do not care if it's the transmission or rear gear giving the multiplication. The driver doesn't care either. The driveshaft seeing more torque doesn't mean it goes up a hill faster. The overall ratio is the same. That's what's important. I'll say it for the last time, a direct drive 10 speed with 2.62's is almost identical to a B ratio overdrive 10 speed with 3.58s. If you have two trucks side by side but match the engine rpm, transmission and by extension road speed, both trucks will pull up a hill or accelerate exactly the same.

You are looking at things one-dimensionally. Just like all the talk about torque. That's one dimension. Telling me an engine produces 3000 ft lbs of torque is irrelevant. I need to know the speed that it produces that torque. I can produce 3000 ft lbs of torque with my body with a 20 foot pipe. The problem is it's at such a low speed that I cannot get work done.

What I just described to you is horsepower. Torque is one dimension, speed is the other, of horsepower. If I told you an engine produces 2000 rpms would you be impressed?

All of the above applies here. Looking at the rear gear only and saying one truck will start better or go up a hill better is like answering "how much power does your truck make?" with "2000 rpms". It's only half the story. YOU NEED THE WHOLE STORY!

The transmission ratios are essential to the conversation. You also ran mostly directs in the 70s correct? Thing is you compare 4.10s to todays gear and go wow, we really had to run lots more gear. What you don't realize is there was an even larger difference in the transmission ratios, it would be like running 4.80-5.00 gears compared to todays overdrive setups.

I've pulled into my fair share of interesting places. 16% grades are fun, better have lots of speed at the bottom.

To prove what I said before:

http://www.eaton.com/rr/ProductsServices/ProductsbyCategory/Transmissions/PCT_308991#tabs-2

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[TD]direct[/TD]
[TD]14.8[/TD]
[TD]10.95[/TD]
[TD]8.09[/TD]
[TD]5.97[/TD]
[TD]4.46[/TD]
[TD]3.32[/TD]
[TD]2.45[/TD]
[TD]1.81[/TD]
[TD]1.34[/TD]
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[TD]2.64[/TD]
[TD]39.072[/TD]
[TD]28.908[/TD]
[TD]21.3576[/TD]
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[TD]11.7744[/TD]
[TD]8.7648[/TD]
[TD]6.468[/TD]
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[TD]11.06[/TD]
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So #### close it's not even worth talking about, around 1%.

Remember what multiplication is. We sacrifice speed for torque, but the horsepower remains the same as before multiplication. 2:1 multiplication gives us twice the torque on the output but half the speed. 4:1 multiplication gives us 4 X the torque but 1/4 the speed. Always the same horsepower.

It's important to remember that when speccing out a truck especially when different transmission ratios come into play. The only time a direct drive transmission matters is taking off, because the driveline sees a bit more shock load than an overdrive setup. That's why they can only be specced to 110k.

 

Let's take this further. Two trucks like the above setup, same tire size, same road speed. Both cruising at 1500 rpms making a max of 1650 torque. That's 471 HP BTW, but not important for now.

They're both in 10th gear and approach a hill. Truck "A" - the direct drive truck - pushes 1650 torque through the transmission. Since the transmission is 1:1, there's no multiplication, and the driveshaft sees 1650 torque. The axles are reduced 2.64 times, so the axles actually see 4,356 ft lbs of torque.

Truck "B" - the overdrive truck - pushes 1650 torque through the transmission. Since it is overdriven, the torque gets divided down 75%. 1650 X .75 = 1237.5. Now put it through the diff, which is 3.55. 1237.5 * 3.55 = 4,393 ft lbs of torque.

Which is exactly what we expect from my previous post, it's within 1%. Truck B is actually cruising 1% slower as well, but that's such a small number nobody cares.

Put 2.79s in Truck A and it will have better startability, better gradeability, better hill pulling than Truck B.

 

it doesn't matter if you have a 5 hp briggs with a 3sp with .62 OD or 5000 hp jet engine with a 98 sp direct, it will not change the amount of torque it takes to turn the yoke on the front of a rear end with 2.62 or 3.70. but 3.70 are easier to turn than 2.62. it still takes so much to turn a rear end no matter what you turn it with. even if over all gearing is the same you still have to overcome the fact that 2.62's are harder to turn.

 

what part do harmonics play with the slower driveshaft speeds at greater torque caused by more powerful O/O spec engines?? and do the bigger, higher tooth count pinions absorb (waste)power at higher loads, ratio change move the peak load to different places, numerically higher ratios place less of the axle torque on the drive shaft, so with numerically lower gears/direct transmission, some where the u joint phase loads may be greater (with increased engine power) than the gearing losses from the overdrive trans/numerically higher gears.

It all maths out on paper, if empirical data is different then the losses are happening somewhere, U joint oscillation/harmonics or greater tooth contact area at a higher torque load in the numerically lower gear set.

 

Direct drive transmissions, take more of the stress, verses letting the rear gears handle more of the torque on an O/D trans.
Maybe the extra leverage of the deeper gears, offsets the extra drag of the O/D transmission?

I think it is difficult to get a 10 speed direct any more with 1850-2000 lb torque rating. One use to be able to, and it was only about a 10 lb. hit.

Also, another consideration, one is spinning the gears more on say a set of 3.55s verses those 2.62s, in the gear oil, and there probably is some loss. How much, who knows..

I too always thought direct transmissions made more sense as well, but like has been stated, maybe not.

$14,000 sounds like a bad bet, but just driving a 100,000 miles a year, with going from a realistic 6.5 to 7.5, would be around $40,000 in 5 years.......I have no dog in this race, but that sounds like a solid investment.