Rear axle question from clueless member..

[Calfdemon]

Excuse my ignorance in this matter, but I absolutely know NOTHING about rear axles or gearing ratios, or how they effect the RPM's, torque, power, or whatever it is they effect. That being said, here comes my ignorant questions that I am embarassed to ask (but once I have the answers, I will then know ).

I currently have a 72 F250 which according to my door tag and the decoder from this site, has a 4.10 Dana 5250# rear end.

I am buying a 69 F350 Crew that according to the door tag has a 3.73 Dana 70.

The 72 has a 390 with a C6 (original) and the 69 has a 460 with a C6 (originally a 390 with a 4 speed manual).

What is the difference between those rear ends and which one is "better"? I am planning on swapping all of the better parts from the 72 to the 69 and then selling the 72 to recover some of my money.

One of the things I did notice about the 69 is that the posts for the lugs appear to be a lot longer and thicker. I also noticed that they are reverse threaded and the lugs that hold the wheels on the 69 are monsters.

I currently run my 5 slot mags on my 72 that I want to keep. The wheels require the deep sleeved, closed end lug nuts to properly hold the wheels in place (the sleeves go down into the lug holes on the wheels). I do not think that the lug nuts would fit on the posts from the 69, nor do I think they are reverse threaded (I have to check, I just dont remember). This would probably require me swapping out the rear ends from the 72 to the 69, but again, which axle is better of the 2?

Of course, the front wheels on the 69 run the same lugs and have similar posts, so I might need to figure out what to do up there too, but I will tackle that at another time if needed.

As always, any info and help is appreciated. Sorry again for the dumb questions, but I think I slept a little too much in auto shop all those years ago...

[Calfdemon]

Ummm... A possibly brilliant and painfully obvious solution just popped into my head as I read this. If I didnt want to swap the rear axles, couldnt I just swap the parts from the rear that have the posts on them? Both have drum brakes on the rear so would the parts be interchangable?

I will probably have to do the front too and that might be trickier since the 72 has drum and the 69 has disc. But I just am clueless when it comes to that area of our trucks... I know I will learn soon enough when they are both here and I dive in. But in the meantime, any knowledge I can acquire up front will surely help when I am hands on...

[fordman]

the larger the number of the ratio the more the truck will pull. but the less gas mileage it will get. you would want to stay with the same lugs and wheels all the way around your truck. that way you dont have to carry two different spare tires. the brakes may not interchange.

[Calfdemon]

Ok, so the 3.73 on the 69 will get better gas milage than if I put the 4.10 on it? I dont really plan to tow with this truck, so I dont think I need more pulling power.

Maybe I can look at ordering new lugs for my wheels to fit the posts on the 69. I have no idea if they even make them that size, but I will have try I suppose... One way or another I will run my wheels on the 69. Thanks Fordman for the input.

[forrestbump]

F350's have 9/16" wheel lugs and F250's have 1/2" wheel lugs. You'll need to get lug nuts to fit PLUS you've got the left hand thread lugs to deal with...that'll require some digging for "Mag" lug nuts with the shoulder you'll need.

Now you MAY want to consider swapping wheel studs to 1/2", right hand thread - OR - if you can find the proper lug nuts that will work on your mags, replace your left hand 9/16" studs to 9/16" right hand studs (this is what I'd do IF I could find the proper lug nuts.

another possibility is to have the lug holes in your wheels bored out to fit a proper lug nut for your mag wheels.

You CAN use the disc brakes from your F250 as long as the king pins are the same size as your F350. My F250 has smaller king pins (a low GVW rated F250) but some F250's DO have the 1" diameter king pins that match F350's. Just compare the two sets of I beam king pins to make sure.

Decisions, Decisions, Decisions...

EDIT: Keep the Dana 70 with 3.73 gears. You've got a 460 so plenty of power on tap. Lower gear ratios are great for smaller motors, not your issue.

[Calfdemon]

Ok, the 3.73 is staying put in the 69... Now to clear up the lug issue:

The 69 is the one with the disc brakes in the front (which I obviously want to keep).

The 72 has drum all the way around.

Is it possible to swap the smaller wheel lugs from the 72 onto the 69, and put the larger wheel lugs from the 69 on the 72? If I would be able to swap those straight across, that would solve my issues. If not, then I have to figure out how to make my wheels work on the 69 with other means.

[forrestbump]

Is it possible to swap the smaller wheel lugs from the 72 onto the 69, and put the larger wheel lugs from the 69 on the 72? If I would be able to swap those straight across, that would solve my issues. If not, then I have to figure out how to make my wheels work on the 69 with other means.

YES! Use a press if at all possible. If NOT available, I've used a hammer and drift to knock out and/or install wheel studs.

Bump era F250's and F350's disc brakes are identical from what I know...that's based on me swapping F350 disc brake parts onto an F250. I DID change the studs to 1/2" from 9/16" on the donor F350 front hubs.