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Does deeper axle gearing HELP or HURT the transmission?

Hey-O said:
Think of it as a 10 speed bike, It puts more stress on your knees in tenth gear than it does in first. In first, it's easier on your knee's, but you're working other parts more because they are now moving much faster. Lower gear 410, more stress on all components behind the rear end , axles, etc. Higher gear 2.76, more stress on the engine mounts, tranny and or clutch.
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This isn't actually correct. A person
5.7 hemi said:
Just putting this out there....... a lifted Ram 2500 with the 68rfe trans using 37” tires with stock 3:42’s puts a HUGE strain on the trans. That’s why people usually install 4:10’s to 4:56’s. A lower gear set will help the trans live longer, at the expense of higher rpm’s on the engine.
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But in fact it does nothing. Torque from the engine is identical, hence torque through the tranny is identical.
 
Why does a tow package come with 392 gears.
 
Not buying that. Torque is multiplied through the trans and multiplied again at the rear and then 1 final time at the tires.
 
5.7 hemi said:
Not buying that. Torque is multiplied through the trans and multiplied again at the rear and then 1 final time at the tires.
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So the engine makes torque that I think we can agree doesn't change depending on the rear axle ratio. The tranny multiplies that, and in the case of the OP's question, we aren't changing the ratios. so we now have "X" torque times 2.45, 1.45 or 1. Where's the extra torque coming from?
 
The rear gears are also multiplying that torque from the trans.
 
In addition to changing the direction of power flow by 90 degrees (from the driveshaft to the axles), the purpose of the rearend gears is to multiply the torque delivered by the engine and transmission. Gears can be thought of as complex levers.

Copied from HotRod.Com
 
The transmission is "transferring" the power, not absorbing all the engines power.
For the transmission to "see" all the power, the vehicle would have to be stopped with the engine outputting all of its power.
Once the vehicle starts moving, the actual power the trans will see it the amount needed to move the vehicle.
Usually if too much power is applied, either the rear rubber fuses blow (smoke the tires), or the clutch(s) slip hopefully before finding a weaker hard part like U-Joints, axle shafts, gears, transmission shafts, and such.

As mentioned, in simple terms look at the the transmission (or other gear ratio) as a lever. The lever only needs to be as strong as the part it is lifting.
The lever is lifting (moving) an amount of weight, but if the lever is prevented from moving on the weight side then the lever needs to be as strong as the force applied to the other side.
That is the simple terms, not including dynamics of how the lever is accelerating (or bending) when moving.
 
451Mopar said:
The transmission is "transferring" the power, not absorbing all the engines power.
For the transmission to "see" all the power, the vehicle would have to be stopped with the engine outputting all of its power.
Once the vehicle starts moving, the actual power the trans will see it the amount needed to move the vehicle.
Usually if too much power is applied, either the rear rubber fuses blow (smoke the tires), or the clutch(s) slip hopefully before finding a weaker hard part like U-Joints, axle shafts, gears, transmission shafts, and such.

As mentioned, in simple terms look at the the transmission (or other gear ratio) as a lever. The lever only needs to be as strong as the part it is lifting.
The lever is lifting (moving) an amount of weight, but if the lever is prevented from moving on the weight side then the lever needs to be as strong as the force applied to the other side.
That is the simple terms, not including dynamics of how the lever is accelerating (or bending) when moving.
Click to expand...
Exactly. And in our case the force applied to the lever is defined by the engine, which doesn’t change in torque characteristics because of the rear axle.
 
put 600ft/lbs of torque into a driveshaft with lower numeric gears and sticky tires your driveshaft will look like a twizzler if the ujoints/yokes don't break! same thing is happening in the trans, the sun/gear teeth and shafts are receiving the same high load, sun/shaft will bend/break/ teeth will shear,whichever is the weakest link.
higher numeric rear ratio will transfer high load to the axles!
 
BB BELLA said:
put 600ft/lbs of torque into a driveshaft with lower numeric gears and sticky tires your driveshaft will look like a twizzler if the ujoints/yokes don't break! same thing is happening in the trans, the sun/gear teeth and shafts are receiving the same high load, sun/shaft will bend/break/ teeth will shear,whichever is the weakest link.
higher numeric rear ratio will transfer high load to the axles!
Click to expand...
Yes, and nothing different to the tranny.
 
the same converter with both a 2.76:1 & a 4.10:1
will act completely different,
Edited; to clarify
especially if the converter was intended to used
is the larger diameter (like 12"-13" 1000-1200rpm stall) converter
used for 2.76:1 gears
it will have almost not stall speed with a 4.10:1 gear
if it's a 10" converter like a 2800-3200 converter, performance converter
it will act like it has far more slip or stall speed, with the 2.76:1 gears
it's intended for use with higher numerical gears, like the 4.10:1

you will have more effective stall speed
(probably heat in stop & go traffic)
& work the converter much harder
with the 2.76:1 vs the steeper gears
far easier to get the car moving
& less effective stall speed with the 4.10:1 (better gear leverage)
with the exact same converter

so yes it affects the transmission,
possible/likely generated heat, the friction/wear on clutches & bands
too if nothing else, especially in stop & go traffic

how the engine cycles & uses it is far more complicated
it can aid in power, to have a looser 'smaller' diameter higer stall converter
(can generate heat too)

a good rule of thumb (ballpark) is to multiply your 1st gear ratio
& the final 'rear gear' ratio to achieve near 10.1:1,
especially for performance applications
depending on what kind of engine
& what kind of converter (or even clutch) you have in front of it,
makes a huge difference too, especially feel
or seat of the pants performance, actual performance too

it's not like an engine dyno,
lots of things are affected thru the drivetrain
gears & converter can make or break a combo
much like the camshaft with the proper gear & converter specs too
even tire size (another story altogether), can & will affect
the transmission & it's life

If that makes any sense

on the same not during regular driving
hwy speeds (not around town per se) the lower numerically gears
like a 2.76:1 gear will tend to run cooler,
not constantly spinning at higher RPMs
a good cooler (especially like a Derale with a fan)
or a deep cast alum. pan with fins (like the B&M)
or cooling tube will drop that temp down some too
 
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If you were pulling 5000 lbs with 276 gear the engine and trans load up trying to turn the rear gears. More gas pedal is needed creating heat the loading up creates. 410 gears turn easier making for less power needed to pull the same weight reducing heat build up. Horse power is horse power, all the torque is in the transmission till it starts to pull away.
 
And this is where weight comes into play.
Less weight, greater torque,, more
horse power=win. A lot already have it
figured out. For us novice builders such
as my self,
Nate S said:
This isn't actually correct. A person

But in fact it does nothing. Torque from the engine is identical, hence torque through the tranny is identical.
Click to expand...
Exactly my point. The same trans used in
two different torque applications. The trans
cares not, what gear ratio is run with an
automatic trans. The torque converter
reacts to the stall. A four speed manual
is a more direct connection and I think
that is where confusion begins. Case
in point:
I have a Jeep CJ7. Stock rear gears 3.55.
Changed those rears to 4:10. Result was
more torque at a lower rpm. Torque plays
hell with axle splines, housings, bearings,
and driveshaft u-oints. Most of these items
failed, and have since been upgraded.
The turbo 400 trans is still running strong
with the addition of a trans oil cooler and
a torque converter that distributes the
the added torque from the lower gears.
What makes a auto trans strong is it's
ability to deal with heat. Trans oil coolers
and increased oil capacity.
 
Gear reduction is power and it’s real simple leverage to move the object... why can an old power wagon from the 40-50s with an ol flat head move a mountain and barely grunt , deep gear reduction at the expense of top speed. The guys from A&A told me the I did the best thing for my Nag1 when I put 3:91 gears under my supercharged SRT Challenger... it makes the trans work easier.
 
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Has anyone making comments in this thread actually driven a car, long term and hard, with 2.76 gears?

I have. My 71 Challenger 318, 8.75” open rear 2.76 with a 904 Torqueflite. Entire rear end was original to car, including the ring and pinion. Had the car for 12+ years, never had to touch the rear end. Trans was rebuilt one year after I bought it, because previous owner put a manual valve body in it and installed it incorrectly. I had it changed back to an automatic valve body.

So after 11 years of spirited driving, the rear end sounded better than my Super Bee does now. The 904 shifted better and sounded better than my Super Bee’s 727. My Challenger could run at 120 mph without sounding like the engine was going to explode and with a ride quality that was smooth and confident.

In contrast, currently my Super Bee is simply not capable of even hitting 80 mph without sounding like it’s going to fall apart. The engine RPMs are much higher and the car was struggling to hit 80.. Feeling very unstable while doing so. Don’t know what gear ratio is in the Super Bee but I’ll be finding that out soon.

I discovered how terrible my Super Bee runs at even moderate “high speeds” when I was provoked by an obnoxious driver of a black Jeep two weeks ago. I’d have much rather been in my Challenger with it’s 2.76 gears that day. It would have been far less embarrassing.. A ******* Jeep showed the Super Bee its tail lights.. It was supposed to be a casual cruise in the Bee until that damn Jeep started tail gating me.

Anyway, I’m guessing the gears in the Bee are 3.55. We’ll see how close my guess ends up being..
 
MoparGuy68 said:
Has anyone making comments in this thread actually driven a car, long term and hard, with 2.76 gears?
Click to expand...
Yes. Had a '69 Barracuda with a 7 1/4 diff with 2.76 gears, 904. Used to hammer it, never any issues. Now have an 8 3/4 with 3.23 gears, 727. Hammer it and never any issues. Both have 318 engines, probably why the transmissions have no issues.

I don't see what your post has to do with the original question. Are you indicating that because your Super Bee feels like it's falling apart and couldn't pull the skin off rice pudding that any gears steeper than 2.76 will cause the same effect in other cars? Your Super Bee is not a prime example going from your previous posts.
 
Don’t forget, the size of tires also plays a factor.
 
I've used 2.76s, 3.23s, 3.55s, 3.91s and 4.10s in my Charger.
The 3.91s were with and without a Gear Vendors overdrive. The 3.55s were with a 727 and now the Tremec 5 speed.
Low rpm, high speed cruising is fantastic whether it is with tall axle gearing or moderate gearing with an overdrive.
The 3.91 and 4.10 gears sure made for snappy throttle response but holeeeeee crap did they suck on the freeway!
 
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