rear end swap

[OldRanger68]

I have a 68 F100with 390-c-6 and 3.75 gears. It's a real screamer but I would like to convert it to simply highway use. I found an 81 F-150 with the manual overdrive trans and I believe it has 2.47 gears (rear end code 17) I would like to switch out the 68 and install the '81 but keep the original if I or someone wants to convert it back. My question is if the rear end swap is compatible except for spring and shock mounts, which I would change to fit the '68. Mainly it is a tracking question. What is the overall width difference and what effect will it have on steering, etc.?

[cep62]

If you have a 9 inch rear you don't have to change the whole axle , just the center section.
Most cars from the 60s and 70s will have a gear set in the 2:78-1 range , and a 28 spline axle, which is most likely what your truck has.
You can swap them out in a few hours and find a used set up cheap.

Mainly it is a tracking question. What is the overall width difference and what effect will it have on steering, etc.?

No bad effects other than the work changing it over, you'll need new spring pads welded on , I'm not sure about the shocks.

Now if the '81 has a 9 inch it most likely has a 31 spline . and 31 spline in a '68 is rare.

[OldRanger68]

Thanks cep62,
I want to replace the entire rear end because I want to keep the original, original in the event someone wants to put it back to original. The difference in splines is also part of the reason to just swap rear ends rather than changing gears. Also, if the '81 gears prove too high for my taste, I can put other gears in it rather than tearing into the original which is in very good condition. My main concern is/was about the track width difference and how it might affect the way it handles.

[cep62]

Did you see this ?
http://www.fordification.com/tech/tech- ... ntials.htm

If you have a 9 inch rear axle you CAN keep the original , under your truck .
You can unbolt the original gear set and swap in a different set in a few hours.
You then can save the original,and it takes up less room than a whole axle.

https://www.summitracing.com/parts/str- ... gKtDPD_BwE

Also make sure your '81 wheel bolt pattern is 5 on 5.5 , '80-82 F100 used the smaller car pattern

[71cc]

I believe 73-81 were the same. The perch spacing widened 3 inches as did the frame in 73. Leaf springs went from 2.25 to 2.5 width. Track width increased closer to 4 inches I believe. Shock mounting ?? You are duplicating the dentside track widths as the front went unchanged in 73.

[RottenAppleRed]

Just do a quick pig swap from a donor with 28 spine axles...which are plentiful. As suggested above, the storage space of the factory center section from your truck will take up much less space than the entire rear end. Otherwise, it's a ton more work...involving brakes, spring perches, shock location, extra width, etc, etc...