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Does deeper axle gearing HELP or HURT the transmission?

Kern Dog

Kern Dog

Life is full of turns. Build your car to handle.
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I've wondered about this but just now remembered to ask it
Let's say your 4000 lb car has a 440 that runs pretty strong and you have a well built 727.
Axle gearing of 2.76 VS 4.10.
Wide open throttle acceleration, time after time.....which gear would lead to an earlier failure of the transmission?
Just my bonehead logic here but I think that the tall 2.76 gear would place more stress on the transmission because there is less leverage to move the car.
Opinions?
 
Makes sense...the taller gear will place more of a load on your drivetrain than the shorter one. Similar to how you can "lug" your engine if you try to gas it while in too low of a gear.
 
Not bone head logic. Better gear/less weight, less problems. Slide the graph around to your application.
 
I don't think the transmission cares what
rear end gears you have. It's a fluid coupler.
The torque converter does, as torque is
it's master as the name implies. Lower
gears, more torque. Lower gears will
place added stress to axle bearings, axle
spines, differential housings, driveshafts,
and u-joints with increased torque
launches. What adds stress to a trans
is heat. This just my humble opinion
of course.
 
1STMP said:
I don't think the transmission cares what
rear end gears you have. It's a fluid coupler.
The torque converter does, as torque is
it's master as the name implies. Lower
gears, more torque. Lower gears will
place added stress to axle bearings, axle
spines, differential housings, driveshafts,
and u-joints with increased torque
launches. What adds stress to a trans
is heat. This just my humble opinion
of course.
Click to expand...
I don't understand how lower gears will place added stress to driveshafts and u-joints? The torque multiplication from gearing occurs after the flow of power has already left those components. The axle splines I can understand; lower gears (higher numerically) increase the torque going through the axles. But, not the driveshaft. If anything, the driveshaft components will have an easier time of it during normal driving because the 4.10 gears lessen the effort required.
 
Photon440 said:
I don't understand how lower gears will place added stress to driveshafts and u-joints? The torque multiplication from gearing occurs after the flow of power has already left those components. The axle splines I can understand; lower gears (higher numerically) increase the torque going through the axles. But, not the driveshaft. If anything, the driveshaft components will have an easier time of it during normal driving because the 4.10 gears lessen the effort required.
Click to expand...
It's a torque thing. Compare for example
a Jeep Wrangler Sport (4 banger) vs a
Jeep Wrangler Rubicon (6 banger).
The Sport has much higher gears,
lower strength of drivetrain components, vs the Rubicon's Dana 44 and bigger/stronger
driveshaft and u-joints. Torque transfer
starts at the torque converter. Hence,
the same auto trans is used in both
vehicles. The torque converter is the
point of power/torque transmission
to the drivetrain. The more torque applied,
the faster you're gonna go, given your
gear ratios, as torque is the ability to get
you to speed.
 
The extra wear on the drivetrain with the 2.76 rear makes sense in a "wide open throttle all the time" scenario, but in the real world people with 2.76 gears probably drive more gently, plus the gears themselves are turning less revolutions, so it may even out overall.
 
Last edited:
66 Sat said:
The extra wear on the drivetrain with the 2.76 rear makes sense in a "wide open throttle all the time" scenario, but in the real world people with 2.76 gears probably drive more gently, plus the gears themselves are turning less revolutions, so it may even out overall.
Click to expand...
I don't think people with 2.76 gears drive
more gently as it's only what the car will
allow. Indy cars turn 12,000 rpm' and
achieve speeds of 200+. Their torque
numbers are not on par with 440.
An Indy car on a drag strip would suck.
 
Think of it as leverage with a short pry bar you have less leverage, long bar big difference ... same rule applies to the gears highway gears will move the leverage or change it...
 
Almost no difference. At least if there’s no tire slippage. The two places there would be differences are at the start and at the end. At the start the 2.76 will get going more slowly so the converter will be multiplying for longer but just marginally. At the other end the tranny will spin farther through 3rd gear but who cares?

For all the rest of it you’re putting in and getting out the same torques in the same curves. With the 4.1:1 you go through those curves more quickly but there’s no additional wear once you’re in a gear anyway. Yes the 4.10’s make it “easier” but that’s only if you back off the throttle to slow down and have 2.76 performance. The question was “WOT”.
 
Garngie said:
Makes sense...the taller gear will place more of a load on your drivetrain than the shorter one. Similar to how you can "lug" your engine if you try to gas it while in too low of a gear.
Click to expand...
Me thinks you mean too high of a gear.
 
Kern Dog said:
Just my bonehead logic here
Click to expand...


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It is a balance between torque load and RPM. low gearing like 4.10's will take some of the load off the transmission by getting the vehicle to move easier, but increase the RPM. This seems to make more of a difference to the driveshaft design and balance where the higher output speeds can cause vibration problems.
It seems like the newer cars are using transmissions with alot of gear ratio in the lower gears, and mild overdrive ratio along with higher rear axle ratios.
Some versions of the ZF-8 have 1st gear ratios of about 5:1. The trans and driveshaft would have to be pretty strong to handle 5x the engines torque.
a 727 or 518 trans only has a 2.45:1 first gear ratio, with a 1:1 (727) or 0.69:1 (518) high gear output.
With the 8-speed transmissions final gear ratio only slightly higher than the 518 at 0.67.

From wiki, the newest 2020 8 speed transmission may have first gear ratio of 5.25:1 and final drive ratio of 0.615:1, the 1:1 ratio happens in 6th gear. If this is true the first gear torque output to the driveshaft/rear axle would be 700 ft/lbs x 5.25 = 3675 ft/lbs of torque!

The 8HP95 (950 n/m = 700 ft/lbs?) used in the Ram TRX uses the 4.71:1 first gear ratio, and 0.67:1 final ratio with a 3.55:1 rear axle.
The Engine puts out 650 ft/lbs of torque, so if the computer allows full power into first gear, the trans output would be 3061.5 ft/lbs of torque and the axles would see 3.55 times that = 10,868 ft/lbs of torque. This does not even include the low gear of the transfer case 2.64:1

Without knowing the torque converter torque multiplication factor, it is still a guessing game. I high stall converter in a 727 might create first gear torque like a low stall converter behind something like the ZF8?

Then you are exchanging slippage and heat in the converter for torque multiplication.
 
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.
 
1STMP said:
I don't think the transmission cares what
rear end gears you have. It's a fluid coupler.
The torque converter does, as torque is
it's master as the name implies. Lower
gears, more torque. Lower gears will
place added stress to axle bearings, axle
spines, differential housings, driveshafts,
and u-joints with increased torque
launches. What adds stress to a trans
is heat. This just my humble opinion
of course.
Click to expand...
Perhaps you didn't write this as intended.
The torque converter is a fluid coupler.
But the transmission uses planetary gears.
A CVT transmission is more akin to what you've described.
 
Last edited:
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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