2nd Gen Non-Engine/Transmission Final drive ratios, carriers, torque ratings... etc.

[sparks57]

I've got some questions about the stock D70 rear I have:



•I'm looking for about 500-550 HP and screw around a lot... am I going to kill my D70? Should I look into a D80 conversion? I'll be running 315 (~35") tires.



•If I can continue to safely run my D70, what is the lowest gear I can run in it without changing carriers if I currently have 3. 55's? (I'm thinking of 3. 73).



•How tough are the stock u-joints? Should I look into converting to the next size up?



•Also, I've been crunching numbers and found that the 3. 73 makes the truck run like 3. 55 with 33" tires (keep in mind that I have a slushbox)... do you guys think that's a good final drive ratio? Or should I look into just getting 4. 10's? 3. 90's make the truck run close to stock when running 3. 15's... . but I haven't found any for the D70 or D80???



Thanks guys!

 

[Mundgyver]

There are a few qustions that come to mind. 1. What are you going to do with the truck??? Toy or Daily Driver?? 2. If it's a toy, how bad are you going to abuse it?? If it is a daily driver, how reliable do you want it?? 3. How big is your wallet versius how bad to you want to upgrade??



Question 3 determins the answer for question 2 which determines the answer for question 1.



These truck will last a very long time and take you anywhere you want to go. Not trying to disuade you from bombing or upgrading, just answer the question posed in order of importance to you. The answers you come up with will determing your needs.



Reliability and durability for the long haul are my goals.

 

[NIsaacs]

The Dana 70 is a good rear axle with good torque capacity. They are rated for 8,000 ft. lbs. of intermittent max torque and 2,000 ft. lbs of continuous torque. The carriers are, 4. 10 and up, 4. 56 and down. The u-joints should be ok with the auto, the auto is more gentle with shock loads. If you are going to hot rod or race the truck, 4. 10's with big tires would be my choice. If not, then I would leave the 3. 55's alone. I like to gear fast, (mph) run slow, (rpm) with the Cummins.







"NICK"

 

[sparks57]

Daily driver, with a lot of stop-light racing. I don't abuse it much, but I'd use the horsepower I'd have frequently. Reliability is important to me... and wallet is no biggy, I'm not apposed to saving!



Not much towing either, maybe a camper trailer, and quick trips with my race car trailer.



So basically should I stick to the "if it breaks, upgrade" phylosophy and just keep what I have?



And the gear swap is going to happen if I run 35's... I feel like this thing is geared too high already!