# what the HECK?????????

Discussion in 'The Garage' started by adamforsythe, Aug 27, 2005.

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Hello,
This is going off from another post (THE "10 bolt strength " post)
Is this true????
Do gears really act as "torque multiplier". Let's say you have a 350 pushing 355 foot pounds and is backed with a TH350/NP208 and 3.73 gears up front and in back when you put your truck in 4L you will be making like 4000 foot-pounds at the back and front wheels.

If this is true how would you do the math?
Thanks

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I found the "Math" Torque x Trans Ratio x T-case ratio x Axle Ratio
So a 400 foot pound engine with a Th350 (first gear) and a NP208 (Low gear) with 3.73 rear and front ends will be making 9813.1824. That is 2453.2956 foot pounds going to eash tire. I don't see that happing that would twist a axle shaft as soon as you put it in gear.
Thanks

3. ### SUBFAN1/2 ton status

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4. ### sandawgk53/4 ton status

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The torque mulitiplication is the whole reason for going to a lower (higher numerically) gear ratio. If it was 1:1 it would require a greater amount of torque to get the axle turning. If you increase the ratio to 4.10:1 for example it has the effect of increasing the "leverage" arm by a factor of 4 and therefore requires approx 1/4 of the torque to get the same amount of mass moving however it does require to move (i.e. the driveshaft revolutions) 4 times as much. Does that make sense or have a thouroghly confused you. That have tools called torque multipliers that you can use with wrenches and they are nothing more than a planetary gear reduction.

Ira

5. ### HarryH31 ton statusAuthor

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The numbers are right (minus a small percentage for frictional losses). Now you can see that A) axle shafts are incredibly strong, and B) why they break so often.

Try driving a manul trans rig and starting from a standstill in 4th gear. That's a 1:1 ratio in most manuals, so there is no torque multiplication. But you do still have the torque multiplication in the diffs working in your favor. It takes a LOT of torque to get a 6,000 lb. rig moving.

6. ### HarryH31 ton statusAuthor

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Another thing to consider is transient spikes that get applied to the drivetrain. The numbers above are making the assumption that power is being constantly applied in a vehicle that has good traction at all 4 wheels.

When a tire starts spinning in the air and then comes down on a high traction surface (such as the ultra-grip sandstone in Moab), the inertia stored in the mass of the spinning components of the engine, flywheel (or torque converter), transmission, driveshafts, diffs, axles, and tires/wheels gets instantly applied to the drivetrain. For a few milliseconds, the drivetrain is seeing a huge spike in torque being applied to it.

Think of it as the difference between an NFL linebacker just pushing against you steadily vs. the same NFL linebacker running into you at full speed. In both cases, the weight of the linebacker is the same. But the inertia stored in his 350+ pounds running towards you does a LOT more damage on impact...

Now it should be easier to see why so many folks post up pics of exploded diffs, gears, axle shafts, etc.

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