78 Dually donor for my 68 GMC Dually

[My Alter Ego]

Ok, so I found a 78 Chevy Dually donor to use in updating my 68 GMC Dually flatbed. I've read (and will re-read) a number of threads regarding swapping out the front end from this 78. What I'm still unsure/unclear about is whether or not the rear end from the 78 will be a direct bolt in on my 68. I guess I'm concerned about the spring perches being in the same location between the two years. Will I need to cut the perches off the 68 and weld them onto the 78's housing? Are/is there anything else I should be aware of. I won't be picking up the 78 until this Friday so a can't measure anything for comparison purposes. Any help, knowledge, tips or suggestions would be greatly appreciated. Thanks in advance.

[87lm7]

I did the same thing with a 78 donor and a 67 1 ton, both trucks were cab and chassis trucks and the rear spring perches lined up perfectly. I swapped the compleat front cross member from the 78 into the 67 and only had to ream two holes and drill two new ones, everything else lined up, even the bolt holes for the idler arm.

[Tx Firefighter]

Ego, keep in mind one important detail that is in 87lm7's post. He used a cab and chassis donor. That's a narrow rearend. You're mentioning using a dually donor. If its a true dually pickup, the overall rearend will be significantly wider than what you have now. Your current 68 is a cab and chassis. Not saying it won't work or to discourage you, just beware that the end product will have a wider rear track which might affect your bed options.

[My Alter Ego]

Thank you both for your responses. Yes, the 78 is a dually pick up and not a C&C and I wasn't aware that there was a width difference. With that in mind would any of you happen to know the widths for either or both of these rear ends. Not having the 78 here makes it difficult to determine its width. I'm certain a local shop could narrow it if necessary. By the way Tx Firefighter, I really appreciate the build thread you did on your flatbed. It's been a priceless resource for info, ideas and tips, thank you for your efforts and attention to detail.

[SS Tim]

This should get you in the ballpark.

[My Alter Ego]

That illustration is perfect! My thanks to all that who have responded, I greatly appreciate your assistance.

[Aruba1]

Hello, I am not sure about the 78 but I will comment on the 89 (w/Dana 70HD) conversion that I just finished on my 72 C20. The spring perches or leaf plates that to be moved 1" inwards. It's a good idea to have the differential on leveled ground and have a degree finder handy (about $5 at HF). Also make sure the plate is level to the differential before you start welding. The pinion yoke is different and uses a strap system instead of small u-bolt to bolt onto the universal joint. The park brake lines are different and need some mods to work on the later model differential. And you need 4" u-bolts and plate since my 3/4 ton had 3" diff tubes (I got them off ebay from a used 3/4 ton dodge ram that uses 4" tubes). Other than that, it's a straight swap :-).

The front end parts were easy too and a straight bolt-on. On my 72 front-end, the front-end parts were still stock. I replaced the lower ball-joint, re-used the uppers but installed new boots (the balljoints were really tight and in as-new condition) and replaced the outer/inner tie rods. The brake hoses had to be replaced with newer style brake hoses to work and welded some brackets on the a-arms. Funny thing, the brake line on the driver side has a different fitting size then the passenger side. In order to install the new brake hoses, we had to put new brake line from the t-fitting on for it to work (I believe it was a 20" line but I could be wrong). The truck drives great. The updated front calipers are much larger than the old calipers. The pads by themselves are about an 1" longer. The rear brake drums are considerably larger, I believe about 3" larger diameter. I am very happy with the upgrade. Next is to install 1980-1988 trimmed coil springs to gain an additional 2" clearence and in the near future a 5 speed tranny.

If anyone knows where I can find those flat wrecked 1980s bumper around Birmingham, AL, please drop me a PM. Thanks

[StingRay]

As I understand the 14 bolts a 3/4 or 1 ton single wheel pick up rear end is the same width as the CC dually rear end. Of course the hubs are different but you have those and all the dually brakes already. The P.O of my truck used a 3/4 ton 14 bolt FF in my 69 and actually used the original 69 ho72 brakes on it. It is actually running the single wheel hubs too with longer studs. Fits real good. I'm stuck looking for some 14 bolt dually brakes now as the 69 drums are made of unobtanium. I can't speak for spring perch location on the single wheel axle as I don't know what all he did to get it in there.