Question: If I have a Dana 30 and put in 4340 chromoly shafts with 27-spline inners and outers, and large 297X or 760X U-joints, will it make it as strong as a Dana 44 or strong enough to run 37-inch-tall tires?
Answer: I can answer both questions with a No and a No. OK, so let's now go into a bit more detail. First, the housing and axletubes on a 44 are a lot stronger and beefier than those on a Dana 30, which results in less flex. Flex within the housing can actually pull the ring gear away from the pinion gear to the point where not full contact is made and gear breakage will occur. Next is the fact that the ring gear on a Dana 44 is 811/42 inches, while the ring gear on a Dana 30 is only 711/48 inches in diameter. This is also true with a lot smaller pinion as well as the pinion shaft. This all relates to fewer teeth in contact between the ring and pinion.
Now if you compare a high-pinion Dana 30 to a standard-rotation Dana 44, as most vehicles use up front, then the strength factor gets a bit closer-maybe somewhere in the middle between the two, maybe a bit less. This is because a standard-rotation 44 is driving on the back side of the gear teeth while a high-pinion unit is driving on the correct side.
OK, now we can get to axleshafts. Dana 30s use a 27-spline axle of 1.13 inches in diameter, while most Dana 44s use a 30-spline, 1.31-inch axle. While this doesn't seem like a really big difference, when engineers work it out with their magic math, there is a major difference in strength. OK, but what about using the chromoly axles? Well, they come close, but still not quite as close as one would think.
There is another option. Use a special ARB Air Locker that takes the 30-spline axle. Now we are up to the 44 in strength, and in fact better than a stock 44 axleshaft. But remember, we are still using that small Dana 30 ring-and-pinion and a housing with not nearly as much strength in it.
Will it handle 37-inch tires? Sure, but for how long is anyone's guess. If you drove the vehicle only on easy trails, maybe a long time. But put a tire up against a big rock and stand on the skinny pedal, and most likely you're going to clean the teeth right off those gears. Is it worth taking the chance? I don't think so. In fact, depending on the weight of the vehicle, gearing, torque available, and driver's state of mind, a 37-inch tire just may be too big for a Dana 44, even with chromoly axleshafts.
Question: I have an '01 Chevy HD Crew Cab shortbed with an 8.1L and an automatic. I have a 6-inch lift with 35s and I do a lot of towing. The truck has almost 130,000 miles on it and runs great, but of course, the mileage really sucks. How big a deal would it be to put a Duramax in it, or maybe even a Cummins? I know I can come by a Cummins a lot cheaper than a Duramax, but would the adapting process be too costly?
Answer: If you think that the diesel swap is going to save you money, well, think again. My guess is that the payback time after all the work is done will be about another 130,000 miles, and that is not counting all the time and labor you're going to have in the truck, as well as getting it smog-legal if you live in a state with inspections.
The easiest motor of the two to fit into the engine compartment would be the Duramax, naturally, as it was first offered in 2001 in your truck. Where the big problem comes is that there are two separate computer systems-one for the engine and one for the transmission-and they "talk" to each other. Jim Brightly, founder of the Diesel Page (www.thedieselpage.com) has made this conversion on his street-rod truck, an '89 Chevy 11/42-ton. Needless to say, it was not an easy task, and he ended up grafting the diesel's dash to his cab to get everything to work right and proper. In the end, it came out looking nicer than factory. I am not sure if the gas motor's dash on your truck is comparable to the wiring of the diesel engine's, so it's something that you would have to check out. There are lots and lots of electrical components to make this diesel run. My guess is that you would also have to swap over to the Allison transmission.
The 12-valve Dodge/Cummins diesel in some ways may be the easier swap, wiring-wise. I believe motor mounts are available from www.autoworldmt.com/Page_9.html. There seem to be some clearance issues with the taller and longer inline motor. This is solved in two ways: modifying the frame to sit the engine down lower, or raising the body a couple of inches with a body-lift kit. There may even be some clearance issues with the A/C pump bracket. I have been told that Cummins offers an A/C compressor bracket that mounts the compressor up high next to the alternator (PN 3930888), which cures the problem.
You could use your present transmission with an aftermarket stand-alone computer system and a performance rebuild, as adapters are available to mate the engine to it through a Cummins dealer. I think that it would be easier to just use the complete matching transmission and transfer case from a Dodge truck. Steve Rumore at Avalanche Engineering (www.avalancheengineering.com) has done several conversions but these have been on earlier trucks.