73-74 to 78 frame and rear differences.

[chevymad]

I've got 3 trucks that i'm putting together to make 1. The first one is a 73 C10 original 454/th400 truck. Bought the truck cheap to get the engine/tranny for another project. Then my brother gave me a rusted out 74 3/4 ton, good running gear-no motor or tranny. Then I inherited a 78 crewcab, again rusted out, but has a 91 crate and working th400.

Anyway, after stealing the 454 out of the 73, I realized I still had enough parts to make 1 decent 3/4 ton, 350 powered truck. So I took the front end,crossmember and all, out of the 74 and installed it in the 73. This is when I found out the 73 1/2 ton 454 frame is 3/4" TALLER then the 74 3/4 ton frame. The 74 and 78 3/4 tons are both the same. Weird I expected the 1/2 ton to have the lighter frame. So I had to use the 1/2 ton lower engine frame mounts to make everything work.

Now today I go out to put the 78 14bolt rear into the 73. I pull the old 12 bolt out, install the exhaust while everythings open and easy. Then roll the 14 bolt springs and all under the truck.. ACK! It's a couple inches too NARROW! I measure across the leaf springs and the 78 3/4 ton measures 42 1/2" the 73 1/2 ton measures a hair over 45"! Curious I go out and measure the rear under the 74. It's the same as the 73 1/2. Looks like i'll be pulling that rear out now.

Measuring the width of the frames all are the same, the difference is in the mounting brackets. I could cut all the rivets off and change brackets, but since I have a rear that will fit, I wont go that way.

Always thought these 73-80 trucks were nearly the same, but theres alot of differences that dont show.