What kills axles - Horsepower or Torque?

[Edahall]

The reason I ask is because I recently purchased a 2 door 1996 Tahoe that originally had a 350 Vortec with 255 hp and 335 lb·ft torque. However, it was converted to diesel and has approximately 210 hp and probably pushing around 600 lb·ft torque at 1600 rpm's. The rear axle is a 10 bolt and 3.42 gear and was not upgraded. I'm thinking that since the gas engine put out more horsepower, it would be harder on the axle than the diesel engine. Yes I know that torque is what is hard on components but torque multiplication already occurs before the power is applied to the axle. You wind that Vortec engine so that it's putting out 255 hp and it's going to put more torque on the axle than the diesel engine that puts outs 210 hp at 1600 rpm.

Here's some pictures of the diesel engine in the Tahoe to prove it can be done.

http://img.photobucket.com/albums/v48/rhedahl/P1020430.jpg

http://img.photobucket.com/albums/v48/rhedahl/P1020431.jpg

[rustyk]

You wind that Vortec engine so that it's putting out 255 hp and it's going to put more torque on the axle than the diesel engine that puts outs 210 hp at 1600 rpm.

Actually, it won't, as HP is essentially torque x RPM. Short-stroke (gaso) engines develop their HP at high RPM; diesels produce more torque at lower RPM.

However, unless you are using the truck to pull very heavy loads, the torque shouldn't overstress the diffy. The 4L80E tranny in stock form is rated at 450 lb-ft, though.

[Edahall]

Actually, it won't, as HP is essentially torque x RPM. Short-stroke (gaso) engines develop their HP at high RPM; diesels produce more torque at lower RPM.

However, unless you are using the truck to pull very heavy loads, the torque shouldn't overstress the diffy. The 4L80E tranny in stock form is rated at 450 lb-ft, though.

This is what I thought. So it's heavy sustained power that'll kill an axle?

Luckily the truck has an NV4500 5 speed manual that's strong enough to handle the torque of this engine.

[More Power]

So it's heavy sustained power that'll kill an axle?

;)

The relatively small wear surfaces in a 10-bolt can shear through the oil film under a heavy sustained load. Heat builds till the lube fails, then hard parts fail.

One of Dodge's learning trials in the early 1990s was how big of a rear diff the 5.9 needed to live while used for heavy towing in the high summer heat. A big diff and synthetic lube cured the failures.

Jim

[Robyn]

Just driving down the boulevard, you will likely never hurt the little 10 bolt.

I have had some pretty nasty 454's in K5 Blazer and used them hard and not broke the diffy.

One thing that will break stuff quicker than you can shake a stick at it, is high loading then unloading then reloading it again with a BANG.

Off roading with a lot of wheel spinning and grabbing is the quickest way to break things.

I put 200K on the old late 70's K5 with the 54 motor in it and never broke anything.

Heavy towing under hard pulls can certainly cause lube related failures.

I would not worry too much about the little cummins breaking your 10 bolt unless you take the rig out and FLOG it hard

Enjoy the Cummins Tahoe.

Missy

[SoTxPollock]

What kills the gears is shock loading to the extreme causing the pinion and ring gear teeth to depart from each other, not a pretty sight and it's accompanied with a very loud bang. You wouldn't experience that with a torque converter in front of the trans. it helps load the differential in a non shock manner. Just use synthetic gear lube and don't sweat it. Installing a standard, trans, don't pop the clutch and you won't hurt the differential gears.

[convert2diesel]

The only issue I have with the 10 bolt is the bearing configuration out at the wheels. By the time you can hear a bad outer going, its already dug a groove in the axle shaft. This configuration is also very intolerant of overloading, as in high tongue wieghts or overloading the back.

Echo the above comments about shock loading and synthetic gear oil. If driven with respect, the 6 banger shouldn't over tax the diff.

Bill