Hey guys new to the /6 but already love it I'm looking to do a performance rebuild in the coming months I have a 1979 motor in a d100 I'm currently wanting to bore it do head work and replace the cam and intake with something better also want to swap the rear end because of such a low ratio please all advice is welcome cause I have no idea what all can be done also someone local that could

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what rear end and gear is in the truck now?

Not sure on the ratio i do know its low bout 60 65 is all you wanna go but that's part of the rebuild that's gonna be swaped as well and as to size not sure but my plan is to have everything work together

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Update the rear end is an 8 1/4 still haven't found a ratio

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A slant is gonna buzz at 65.

Thing is you never really know what someone might have put in an old truck.

Slants usually use a steeper gear because it is needed.
What is the truck equipped with?
Manual or automatic?

If your truck just creeps in 1st you might have the "granny geared" transmission. NP 435? (guessing here).
Being a 100 it shouldn't be the above heavy duty trans.

The 8 1/4 is a standard rear axle for this year truck.

To find the ratio;

Jack the truck up and put the trans in neutral.
Use tape or paint on the drive shaft, to help identify where you started.
Turn the drive wheel by hand.
Count the number of rotations of the drive shaft in a single rotation of the wheel.

That will give you the ratio.
ie; about 2 3/4 turns of the drive shaft will be a 2:73 to 1 ratio.
roughly 3 and 1/2 will be a 3:55 ratio.
I think a 3:23 is in there too.
There are steeper options as well.
Could possibly be a 4:10 or steeper yet.
Taller tires will help lower the ratio, and engine speed.

Thank you for that the truck is currently at the shop right getting a 4 link suspension and air bags put under it and it's a 3 speed column shift first has got some extreme torque and it will run till about 30-35 mph before you half to shift in to 2nd

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