I do a lot of heavy hauling. At what point in upgrading horsepower would I need to go to a heavier drive shaft? Also what other links in the drivetrain would I need to upgrade? I already plan to put a DTT torque converter and valve body in the transmission but what else should I pay attention to? I just don't want to be hauling 14k lbs up a steep grade and hear CRACK!

 

The early trucks with the 727 and 3.07s (and chassis/cabs) came with the heavy walled 4" driveshaft stock. Your truck has a 3" driveshaft. If you want an upgrade I'd source one out of another truck and have it lengthened or shortened to fit your application. Otherwise you'd have to have a custom 4" driveline fabbed up and that gets $$ with all the cost of new yokes etc.

I had a two piece driveshaft from an 89 D250 lengthened to fit my Club cab. Works great.

I wouldn't be TOO worried about the driveshaft at highway speeds with all the power you are making. It is breakaway torque events from a stop in 1st gear (or lower/low range 4wd) that will pretzel a driveline or break pinions OR spread diff housings...

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I think you could make a case for a rear end upgrade before the driveshaft. 2nd gens with NV4500 have a Dana 80 with 35-spline shafts vs. your D70 with 32-spline shafts. However, they have the same size driveshafts.

 

I think that is a good idea, I'm going to check out the local junkyards to see if I can find a 4" driveshaft. Does the larger driveshaft use the same size universal joint as the 3" shaft?

 

My truck weights 7000# at the curb with me in it. The trailer I pull weights 4000#. The Duece and a half weighted over 13000# empty. Add fuel, oil, coolant, canvas etc. and you are looking at about 14000#. I ran from Richmond VA to Hampton VA down I64 at 60mph. A distance of about a hundred miles. Sometimes at full throttle. The stock drive shaft is still going strong. I haul tractors through the mountains of VA,WV and PA. usually grossing out at 20,000 pounds. No problems with the drive shaft. The only major problem is cooling. I really have to watch the engine and exhaust temperatures. Oh, and the fuel gauge.

 

A good drive shaft shop can hook you up for decent price. My custom drive shafts for my Toyota Cummins project were only like $150.00 each and I provided the yokes. With drive shafts wall thickness isn't as important as overall size, or so I'm told.

 

Hey Cactus Pete,

All driveshafts 3 and 4" in 1989-1993 Dodge Cummins trucks use 1410 yokes/ujoints.

 

Boatnik, are you using a 3" or 4" driveshaft?

 

I do like the idea of having a heavier rear end, I did a little research on the 80 and they made some of them with 37 spline shafts too. Would be nice to find one of those, plus they use the 80 in F450's which are rated to haul 24,000 lbs. I wonder if it would bolt up to my 250 without modifying mount position.

 

You won't find a '1-ton' Dana 80 with 37-spline shafts and/or that enormous load capacity. However, you benefit from the amount of torque the larger r&p can handle. You can slide a 37-spline shaft into most, but some builders insist on boring the spindle for extra clearance.

For that extra 24,000# beef you need to to step up to the F450/550 or GM 10-lug versions. Reason being the spindles are physically larger and carry bigger bearings (about 1/4" larger diameter iirc); also bigger brakes. Here is a thread where a guy modified a GM 10-lug version to fit 8-lug wheels: http://www.competitiondiesel.com/for...ad.php?t=64360

Unless you want a bunch of fab work, I'd suggest a 2nd-gen D80 (perch spacing the same) and upgrade the shafts when you manage to break one.