What are the key differences between the C4, C5, and C6 Trannys , what applications are each best used for and what was the production run on them.
Can any current tranny be compared to these old reliables?
I have what I believe is the C5 since it has overdrive but am not positive since the Id tag is missing.

 

I don't know about the C5, but the C4 was typically used behind smallblocks in passenger cars and maybe Broncos and 1/2 ton trucks. The C6 was used in 3/4 ton and 1 ton trucks behind small and big blocks and diesels. It's pretty much the big dog of Ford auto trannys, about equal to a GM TH400. The C4 and C6 had no overdrive. The overdrive replacement of the C6 was the E4OD/4R100. The overdrive replacement of the C4 was the AOD/4R70. The C6 was available in the '70's through the mid '90's. I think the C4 had a similar production run. The overdrives started comming out in the late '80s.