Ok, I have a 78 King Cobra and yes I do not know what rear end is in it. Can somebody help me. What rear end came with the 78KC stock. I know it's stock and I am sure I am going to have to make some changes with the new 351W that I put in it. I am sure something is going to go once the engine is broken in and I stomp on it. (I really dont want to put this thing up on jack stands AGAIN if I dont have to) Sincerely, Patiently waiting to "snap" something!
Its pretty much got to be an 8" rear. The real question is what ratio and if it has a Trac Loc differential. You door tag should have those codes if the rear (and the door!) are original. My bet is on a 2.89 gear, single trac rear. If your 351 is backed up by an auto trans and you don't plan in using race slicks, the 8" should survive a while. Otherwise all bets are off!
All II's came with 8" gears, and a quick way to find out the ratio is to look on the driver side door tag under "axle". '77 - '78 O = 3.00 trac lock 3 = 2.79 open 6 = 3.00 open 4 = 3.18 open 7 = 3.40 open
The original poster stated the car was a KC, so perhaps in that regard one could say they all had the 8 in rears. However, the trac loc was not available in 78.
I had a 78 King with the 302, Rad4, and a 3:00 non posi 8". The complete rear is now in my 75 coupe replacing the Detroit that just happened to fall apart one day. It works ok for regular street duty but I don't woof on it because I don't want this rear to fall apart yet.
This is very true , I am also pretty sure that posi WAS NOT available in 78. Look up mustang II network or Mustang II .ORG you will find all the numbers & decoders you are looking for. These are two great sites.
So there's no such thing as a KC with Traction-Lok? 'hard to believe. Traction-Lok was included with the Rallye Package, according to: http://www.mustangii.net/1978/78opt.asp
Maybe I stand corrected ,BUT under available axle ratios there are NO loc diff's listed under the model 78 year. My brother had a 78 cobra and it was single wheel squeel. Posi should have been standard on a cobra opt. Things were goofy back then though . You could actually order a car w/ diff options. I had a 74 II that had a ( original) 4 banger and 8" rear !! (decoder says it should have been 6-3/4 )
