8 lug rear-end & 5 lug front end...looking to change it.

I've got quite the dilemma with my pickup. Back in the day my grandpa swapped the 5 lug 1/2 ton rear-end with a 3/4 ton rear-end. I'm not sure what the gear ratio is or where to find out. The front end still has the 2wd 5 lug oim twin i beam.

I only want to carry 1 spare tire. Do I swap out the rear end with another 5 lug? Or is there a way to change the 5lug pattern in the front end to an 8 lug? Can i swap out spindles?

Also, my grandpa put in a new aftermarket transmission. So if i swap the rear end again, i will likely need a new drive line special made.

If i was to keep the 8lug rear end, i feel like i will need to install a small lift on the front to level out the pickup. I bet it slopes to the front about 3-4 inches.

Any thoughts help!
I'm not super mechanically savvy, but that's why i have this project so that i can learn.

Thanks guys!

Unless you're just trying to haul more than the truck should, I'd change the rear axle back to 5 lug axle.

I'm pretty sure changing the front would get pretty involved.  Even if you could swap out spindles you'd still have the brakes to figure out.  You couldn't put F-150 5-lug rotors on the F-250 hubs, you probably couldn't put F-150 calipers over F-250 rotors, and you probably couldn't put F-250 calipers on the F-150 knuckles.

So I agree, the rear axle is likely to be the easiest.  Get a complete axles, including brakes, and slap it in.  Likely you'd be able to bolt it to your existing springs (get new U-bolts).  You might need to get a little creative with the driveshaft (it might need to be longer for the F-150 axle, and the U-joint might not be the same, and this would be true even with the stock tranny).  I'm not sure but I wouldn't think hooking up the emergency brake cables would be too hard.  And the brake lines should go on just fine.

However I don't think you'll lower the rear end 3-4" by replacing the axle.  I'd guess less than an inch.  So if you want to address that you probably will need to either lift the front or get stock rear springs (if your grandpa put stiffer springs in to go with the heavier axle).

On the gear ratio, safely jack up one rear tire, put the trans in neutral and count how may times the driveshaft turns as you turn the tire TWO full revolutions.  If you can't turn a tire that way, then you probably have a limited slip diff.  In that case safely jack up both back tires and count driveshaft revs as you turn the tires ONE full revolution (with a limited slip you should only have to turn one tire, the other should turn the same direction and the same amount).

If the driveshaft turns about 4 and a half turns you have 4.56 gears.  A little over 4 turns would be 4.10 or 4.11.  A little under 4 turns would be 3.73.  About 3 and a half would be 3.54 or 3.55.  Three and a quarter is 3.25.  A little over 3 is 3.08.

(Edit:  Oops, no 3.25.  I meant to say 3.23)

An 8-lug axle probably has between 3.54 and 4.11.  Others here can probably narrow it down for you better, but a 5-lug axle is more likely to be 3.55 or lower.

Since you have a 2WD it's not that critical that you get the same ratio that you now have.  In fact, if you don't like how it works, this is a great time to regear (although you will need to recalibrate the speedo if you do).

Now, this is super helpful info!!


“If the driveshaft turns about 4 and a half turns you have 4.56 gears.  A little over 4 turns would be 4.10 or 4.11.  A little under 4 turns would be 3.73.  About 3 and a half would be 3.54 or 3.55.  Three and a quarter is 3.25.  A little over 3 is 3.08. “

Lots of really good info. Thanks! I kinda figured that it would be easier to swap out the rear end back to a 5 lug.

Interesting…I did a rear end swap and kinda regret it.  A lot of work for little reward (so far) but has the potential to be helpful in the future…but want to conform to the GVWR and CGVW.  If the impetus is to carry just one spare tire, maybe carry a can of fix-o-flat and one spare tire?  Many people have concerns about fix-o-flat of course, but at least that’s a 50% solution.  I believe I read once that the factory original spare tire is frequently found in cars brought to the junkyard without ever being used. Alternatively, maybe just mount the second spare in bed of the pick up?  I think there was a factory OEM for this option.

Hope I’m not being a wet blanket…