Drivetrain Rear End Comparison

Discussion in 'Fox 5.0 Mustang Tech' started by GoldenEagle91, Dec 7, 2013.


  1. GoldenEagle91

    GoldenEagle91 Member

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    Hi guys,

    I've got a 79 Ghia that came stock with a 7.5" rear end in it and I am a bit concerned that once I put my rebuilt engine into it that I may run into some problems in terms of its capabilities. I have been told by numerous people including Chevy guys that the only way to go when it comes to rear ends is with a Ford 9" although I don't have the money at the moment to swap in a Ford 9" from a company like Moser or the like so I am trying to weigh out my options so that I don't end up blowing a rear end apart. Is there anyone who has any experience with beefing up the 7.5" or are more people just sticking with beefing up the 8.8"? I was looking at gears and maybe a diff for the 7.5" but I wasn't sure so I wanted to get some of your guys input. Looking forward to hearing back.

    Thanks,
    Andrew
     
    #1
  2. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    I have had two fox body cars with 7.5" rear ends. One was a manual and a 5.0. I think it survived because my tires broke loose before anything else broke. I added Ford's limited slip differential and had good luck back then. Now I would start with a factory posi 8.8", maybe one with discs. IMHO, the 9" is nice to have for setting and changing gear with - you do the hard part on the workbench. But unless you are running slicks and shock the drive train with a tranny brake or power shifts, you do not need the extra strength and cost of a custom 9".

    Who is running really fast and what was your parts experience?
     
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  3. GoldenEagle91

    GoldenEagle91 Member

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    Okay that makes sense, is there any fabrication or modification that would need to be done to an 8.8 out of an 86 to 93 to go into a 79?
     
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  4. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    Stick with an 8.8. Plenty strong enough for your needs
     
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  5. reldla1996

    reldla1996 Member

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    I second that the 8.8 is plenty strong unless you have a ton more than a bolt on 302.
     
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  6. GoldenEagle91

    GoldenEagle91 Member

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    The engine setup is as follows: 9.0:1 pistons, 58 cc combustion chamber aluminum heads, B303 cam, 650 Cfm carb, 1 5/8 Long Tubes, Comp cams short travel race lifters, aluminum full roller rockers. I had read an article in Car Craft where they did a head comparison and with a very similar setup to what I have they kicked out 350 with my heads. I've got some different parts that are a bit higher end than the ones they used so I'm counting on being around 375 hp and tq. Would a 7.5" be able to withstand that? If I don't have to change anything then I don't want to. I will plan on going to 3.73 gears in the future though.
     
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  7. GoldenEagle91

    GoldenEagle91 Member

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    Would upgrading to an Auburn limited slip diff help strengthen the 7.5"?
     
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  8. reldla1996

    reldla1996 Member

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    The 7.5 will live as long as you don't have a lot of traction; with traction, it's not going to be pretty for very long. Changing the limited slip will not strengthen the rear axle assembly. An 8.8 swap is the easiest and cheapest way for you. Sorry....
     
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  9. GoldenEagle91

    GoldenEagle91 Member

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    Bummer, okay thank you for your input
     
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  10. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    Street tires? You should be fine. Drag radials or sticky tires, you may destroy your ring and pinion at some point.

    8.8 is very easy to install, plenty of aftermarket and cheaper than 9"

    I have yet to see anyone yank a fox 8.8 in favor of a 9" unless they were a serious drag racer with a track dedicated car.
     
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  11. mikestang63

    mikestang63 Mustang Master

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    A properly set up 8.8 can handle 1000 hp. It all depends on how much hp you want to make and how much $$ you want to spend.
     
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  12. GoldenEagle91

    GoldenEagle91 Member

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    Yeah it would be street tires on it. Don't plan on dragging it but I do know someone who has a 8.8 with 4.10 gears out back already.
     
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  13. flstang65

    flstang65 Well-Known Member

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    Just get an 8.8 from an earlier year fox and you will be fine. I am actually running an 8.8 in my race car. Granted, I have done some serious work to it but, none the less, I have faith in a well built 8.8
     
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  14. GoldenEagle91

    GoldenEagle91 Member

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    What have you done in terms of work to it?
     
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  15. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    More so than that. I remember when Alex Vettros ODR car went 7.20s at 190+with an 8.8!
     
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  16. GoldenEagle91

    GoldenEagle91 Member

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    To really beef up the 8.8 the main thing to change is the axles and differential right? I have a feeling that 31 spline axles and such are better but I'm not positive. Correct me if im wrong
     
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  17. A5literMan

    A5literMan Mustang Master

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    For a solid street/mild strip 8.8 rearend throw some 31sp axles,diff,some gears,end cover girdle and if you want a little extra safety weld the axle tubes. You'll be good to go
     
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  18. GoldenEagle91

    GoldenEagle91 Member

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    Sounds great man, thanks for the info
     
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  19. srtthis

    srtthis the guy doing it does every local racers rear end

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    guys have been 6's on an 8.8...plenty of reasons to go to a 9" over an 8.8 but strength isnt really one of them.

    only thing id change on my rear over a streetable rear is the diff. id still run the bolt on bearing ends (9" style) still run the custom made axles welded tubes and the screw in wheel studs.
     
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  20. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    If I recall right, there were years that used both rear ends, depending on if it had a 6 cyl, 4 cyl or GT. I see the catalogs list the control arms as the same for all Fox body Mustangs. I would think it would be a bolt it, unless there is a brake hose fitting issue.
     
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