9 inch rear's differences
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From: Campbell River, BC Canada
9 inch rear's differences
I have a 1984 F150 reg cab 4x2 with a 9 inch rear end and a 351w. Today I was pulling my passenger side axle shaft out because it is in rough shape and I was going to replace it with an axle shaft from a 77 F150 s/c 4x2. I pulled the 77 then pulled the 84's and when I went to put the 77's in the 84's it fit fine except the backing plate didn't fit. The Backing plates bolt holes were much further apart, almost a half inch and the bolt's are much bigger as well. I am just wondering if the super cabs 9 inch rear ends are heavier or something like that. By the way they are both a 31 spline.
I also have a 78 F100 with a 9 inch rear end it is a regular cab, will this one work or do I have to find a newer 9 inch?
Thanks, Mike
I also have a 78 F100 with a 9 inch rear end it is a regular cab, will this one work or do I have to find a newer 9 inch?
Thanks, Mike
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Joined: Nov 2002
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From: Memphis, TN
9 inch rear's differences
I'm not into 9s, but I know there were some called "big-bearing" axles, so that's probably what the '77 is. Get a vernier caliper or maybe just a tape measure and compare the '84 bolt pattern to the '78. In any case, you should be able to take the axle shaft you like to a machine shop & have them press the '84 retaining plate onto it.
Post Fiend
Joined: Jan 2000
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From: Dryden, ON, Canada
9 inch rear's differences
The 77 is probably a big bearing shaft, while your 84 is a late big bearing with a different bolt pattern(same as the 8.8"... )
The 78, you'll have to check it, I know it's 31 spline, but, not which bearing style.
Evan
The 78, you'll have to check it, I know it's 31 spline, but, not which bearing style.
Evan
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9 inch rear's differences
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Posting Guru
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From: Campbell River, BC Canada
9 inch rear's differences
Ok heres an update. The 78 has the big bearing type axle as well so I am kinda stuck for now. When I have the small bearing axle out of my 84 and I am looking at it, I can move the bearing and backing plate up and down and spin them. They move up and down probably about 1/2 of an inch which I am thinking is not good at all. Now the question is, is my axle shaft Done and should I build one of the big bearing axles to swap in or is this going to be as simple as just getting the bearing and backing plate pressed on. I know it is tough to tell without seeing it but all help is appretiated.
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Posting Guru
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From: Campbell River, BC Canada
9 inch rear's differences
Steve83, thanks for the input. I am going to stay with the 9 because I have 2 spares in my yard and for what I use it for the strength will be needed. I will take it into work tomorrow and see what they can figure out. Thanks again
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Post Fiend
Joined: Nov 2002
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From: Memphis, TN
9 inch rear's differences
Originally posted by steve83
8.8" in. They're just as strong as the 9"
8.8" in. They're just as strong as the 9"
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Post Fiend
Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
9 inch rear's differences
The old-timers haven't figured it out yet. 
Most of the new guys are finding the many virtues of the 8.8", like a greater variety of suspensions and accessories. Check out the back of a 4.6L Expedition: 4-link; coils; disks; oversize axleshafts/bearings/tubes... Sweet! 
Most of the new guys are finding the many virtues of the 8.8", like a greater variety of suspensions and accessories. Check out the back of a 4.6L Expedition: 4-link; coils; disks; oversize axleshafts/bearings/tubes... Sweet!
Post Fiend
Joined: Nov 2001
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From: Coutts Canada
9 inch rear's differences
Just yesterday i put some rebuilt axles (new bearings and seals) in my truck. Anyway the axles are out of 75 and they had the older style bearing with the better seals. Anyway with the baking plate just take an air grinder and enlarge the holes inward in equal lenghts (takes about 5 minutes) and there ya go. Be sure to use washers on the drum side. Anyway the bolt patterns are the same. But if you change one side be sure the other axle is a matching one with the same type of seal and bearing. If you have any more questions on this e-mail me and i'll try my best to answer them.
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Posting Guru
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From: Campbell River, BC Canada
9 inch rear's differences
Well not that you called me one but I don't consider myself an old timer yet. I have a 97 Expedition right now and its decent but not built for huge power. The truck is strictly for street as I have my 79 for 4x4ing so I want to street reliability but doesn't need to be able to take an off road beating. I also have to stress the 2 sitting in my yard factor as well.
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Posting Guru
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From: Campbell River, BC Canada
9 inch rear's differences
Well The bearing ended up being on backwards so we flipped it and pressed it then re sealed it and put it back in the truck and like so its good as new. Thanks for all the help folks.
