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Thread: Is a stock differential really "that" fragile?

  1. #1
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    Is a stock differential really "that" fragile?

    Is a stock '55 differential really "that" fragile?

    Back in the 70's my uncle ran a 4:88 geared sock rear with an early posi unit in a 55 BelAir post.
    He ran cheater slicks, a 4 speed, 12.5:1 .060 over 350. He ran mid 12's and says he never broke
    anything in the rear end.

    I am wanting to run a warmed over LS1 in my cruiser. It won't have wide tires and will have a
    4L60e. Am I really in danger of destroying the stock open 3:55 rear?
    I realize I won't have a posi, but do I really need to worry?

  2. #2
    Registered Member chevynut's Avatar
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    IMO as long as you're not racing, you will be fine. There are thousands of these on the road. I had one behind a 427 in my 55 Chevy, and never had a problem with it. I smoked the tires once in a while too. Us rodders always want the "best" even when it's not needed.

    What's the worst that could happen? You break it and have to fix it?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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    56 Chevy 2-door BelAir sedan
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  3. #3
    Registered Member NickP's Avatar
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    Quote Originally Posted by Geoff View Post
    Is a stock '55 differential really "that" fragile?I realize I won't have a posi, but do I really need to worry?
    Noop! .................................

  4. #4
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    To me the stock rear is okay for "every day" driving. But in my opinion, it has to be described as somewhat fragile if you drive any harder than that.

    The #1 weak spot is the spider gears in an open differential. You can break spider gears in an open differential even with street tires and an automatic. On the other hand, a posi unit will just about eliminate that problem.

    The next weak spot is the axle shaft. IMO you probably won't have a problem on street tires but definitely would with slicks, even street radials.

    The wild card is the bearing cap. I broke one with street tires and an open differential. Never did again, even with racing with slicks and a 4 speed.

  5. #5
    Registered Member Maddog's Avatar
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    If you want to bullet proof it, within reason do install a good posi, use this guys bearing caps: http://www.bruneauperformance.ca/cam...gsrockers.html Buy new, good alloy axels , Dutchman's are good, and don't forget good quality spicer U joints

  6. #6
    Registered Member chevynut's Avatar
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    Yes, mine was a posi. I guess that's why it held up to the 427.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #7
    Registered Member Bihili's Avatar
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    Quote Originally Posted by Geoff View Post
    Is a stock '55 differential really "that" fragile?

    Back in the 70's my uncle ran a 4:88 geared sock rear with an early posi unit in a 55 BelAir post.
    He ran cheater slicks, a 4 speed, 12.5:1 .060 over 350. He ran mid 12's and says he never broke
    anything in the rear end.

    I am wanting to run a warmed over LS1 in my cruiser. It won't have wide tires and will have a
    4L60e. Am I really in danger of destroying the stock open 3:55 rear?
    I realize I won't have a posi, but do I really need to worry?
    http://www.tomsdifferentials.com/tomp.htm
    Bill 1957-427-177-6-410

  8. #8
    Registered Member OLKY55's Avatar
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    Back in the 70's, my stock rear was stronger then my driveshaft and my T-10 trans.
    1955 2D HT, 1957 2D Sedan, 2004 Z06 Corvette, http://s1070.photobucket.com/user/OL...?sort=3&page=0

  9. #9
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    I did experience a "bit" of trouble with my 62 409 dual quad 4 speed when I changed rear gears. I found the spiders to be the weak link in the non posi rears, but the posi did seem to take MUCH more abuse. remember that the biggest tires for the street tires were 820-15 Burcrons and cheater slicks. You have much more selection and width of tires today so you may have some trouble!!

  10. #10
    Registered Member 55mike's Avatar
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    I've heard it said " a drag racer can break a bowling ball in a sandbox.." This said, I believe with an automatic and some prudence you will be fine.

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