Transfer Case info

[Scollins]

I know the forum guidelines say "no drivetrain discussion," but I feel this information is applicable to both 12V and 24V trucks, thus I'm posting it here. So, here goes... ...

In the May 2001 issue of 4 Wheel & Off-Road, they have an article talking about the various transfer cases used throughout the years in the industry. Here is the information they posted:
Model Max Torque GVW
NV241 LD 5,555 ft-lbs 8,000 lbs
NV241 HD 5,555 ft-lbs 11,000 lbs
NP205 N/A 10,000 lbs
NV271 7,890 ft-lbs 17,500 lbs

I find it strange that the max torque for both versions of the NV241 are identical, yet the GVW is different.

The NV271 is used in the Stuper Dooties, so they've got the better case than ours. The NV271 is a floor shifted model versus the NV273 (electronic control. ) So, I think that swapping an NV271 into our Rams wouldn't be TOO difficult. Not easy probably, but it might just require a simple adapter. I'm going to keep my eyes open for a used one to see if I could accomplish this.

Now consider this: The NV4500 and the NV5600 both have about the same first gear ratio (5. 61/5. 63). Let's use the HO torque figure of 505 ft-lbs for the following calculation: tq x ratio = t-case input tq. 505 ft-lbs x 5. 62 = 2838 ft-lbs. This is well below the max input torque listed above for either NV241. The maximum BOMBed torque for the manual transmission crowd should not exceed 990 ft-lbs. Switch to the NV271 and you can BOMB up to 1,400 ft-lbs.

The calculation for the auto transmission isn't quite so easy, due to the torque converter. But, let's assume it provides a ratio of 2. 0 when unlocked. The first gear ratio is 2. 45. The equation looks like this: 2. 45 x 2. 0 x 450 ft-lbs = 2205 ft-lbs. The max engine torque for the auto transmission crowd is 1,133 ft-lbs. Obviously, this is assuming the limiting factor is the transfer case, not the automatic transmission! #ad
Using the NV271 t-case, an automatic owner could go to 1,610 ft-lbs! Any bets that the auto could handle this much power, even with DTT parts?

Now, I need to find the NV271, get some DTT goodies for my automatic, and go CRAZY! What would be the next "weak link" in the system after transmission and transfer case? Drive shaft? Rear axle? I think the u-joints in the drive shaft would be next... ...

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Scott Collins
'98 Ram 2500 4x4 12 Valve Cummins. Slightly BOMBed! #ad

Renton, WA

[This message has been edited by Scollins (edited 04-09-2001). ]

 

[Craig DeYoung]

Scott,

According to some Dodge info I have from 1995, The NV241 has a max input torque of 1028 lb-ft and the NV241HD has a max input torque of 1400 lb-ft. I think the NV271 has a max input torque of 1600 ft-lb but I'm not sure. I think they come up with these ratings by working from the tires forward. A truck at GVWR can only generate so much torque at the road-tire interface before the tire slips. The load at the tires's OD when this occurs is the tire's coefficient of friction times the normal force (which is the vehicle's weight on that tire). Once you have that load and know the the tire's rolling or static radius, you know the torque at the axle, and you can work back to the transher case through axle gearing. They likely do their durability testing based on their calculated answer. I guess the stickier your tires and the heavier your truck (and the more you BOMB, of course), the more you have to worry about breaking your transfer case.

Craig

 

[Scollins]

I pulled those figures straight out of the magazine. The header on the box indicated "New Venture Gear Transfer Case Ratings. " Also, this can be verified on New Venture's website: http://www.newventuregear.com/tcases.html

With a maximum torque of 505 ft-lbs, multiplied by the first gear ratio for the manual transmission, you have 2838 ft-lbs at the transmission output/t-case input. Guys would be shredding their t-cases at 1600 RPM if the case was only rated for 1000 or 1400 ft-lbs. Since an un-BOMBed Cummins doesn't normally suffer from clutch slippage, I assume the clamping load on the stock clutch is high enough to transmit this power 100%.

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Scott Collins
'98 Ram 2500 4x4 12 Valve Cummins. Slightly BOMBed! #ad

Renton, WA


[This message has been edited by Scollins (edited 04-09-2001). ]