Mopar Action On-line – Tech Questions


Tech Question

Doug Tracy, Kidder, MO, 1980 Dodge F-M-J body 318

Rick, I need you to end a argument that I’m having withsome members on The argument is about the 7-1/4″ and 8-1/4″axle. Many F-M-J body owners, who are members on that website, are are ledto believe that most of their cars are equiped with 7-1/4″ axles. Onemember even flat out told me that no Diplomat was ever equiped with a 8-1/4″axle. Several members say the only way to tell which axle you have is by theaxle tubes and not the diff cover. They say the later 7-1/4″ axles have 3″tubes and taper down at the diff to 2.5″. They claim it has 10 bolts on thecover unlike the earlier 9 bolt 7-1/4″ axles that I’m familier with. I knowthat 7-1/4″ axles have 9 bolts on the diff cover and is irregular shaped,while the 8-1/4″ has 10 bolts and the cover is oval shaped.

I’ve referred back to the Oct 1989 article “Bringing up the rear” (yeah, Ikeep all my old Mopar mags). Your article seems to agree with me. Couldyou shed some light on this so called 7-1/4″ axle that these F-M-J bodiessupposedly had?

Doug, both axles were used in F, J, and M’s, from the beginning in 1976right through the end in ’89. That’s a fact you can take to the bank, I haveboth factory documentation and personal, firsthand knowledge of these facts.The surest I.D., at least the one I’ve always used, is the cover shape,”regular, oval” (8.25″) vs. “irregular, angular” on the 7.25″. Over theyears there were several design changes that make the other factors lesspositive — remember, the 7.25″ was released in 1960, and the 8.25, as Irecall, in 1969. These are no spring chickens!

If I had to take a guess — and this is ONLY a guess — I’d say that, overthe 13 years of production, something like 75% of these cars had the 7.25″.Virtually 100% of the 360 cars, and nearly all 318 cop cars, had the 8.25″,while it seems like close to 100% of the 225 cars had the 7.25. Civillian318s were the crapshoot, the factory had a matrix of applications thatdepended on axle ratio, Sure Grip Y/N, wagon, tow package Y/N, etc.

So there’s the light you asked me to turn on. Looks like everybody’s right,and everybody’s wrong — but at least the argument is over. As a recenthumorous graphic that was sent to me pointed out, (present company excepted,of course) — arguing on the internet is like running the SpecialOlympics — even if you win, you’re still retarded.



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