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Thread: Teach me about 9" rearends

  1. #1
    Member JOURNEYMAN
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    Teach me about 9" rearends

    I always have used 12 bolts but I hear 9" is stronger.
    I also see 28-40 spline axles which is the best to have , how many splines

  2. #2
    Senior Member DYNO OPERATOR
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    A built 12 inch is stronger than a factory 9 inch

    The only way a 9 inch is strong is if you invest some money into it.

    The more splines an axle has usually it is also larger in diameter. Larger if all else is equal is stronger.

    Very few cars can be powerful enough to twist top quality 35 spline axles. I have seen above 3,000 hp on Mark Williams 35 spline with no isues. I have also see a couple of other brands damaged with 35 splines with 1,600 hp (appx) in addition to tire shake.

    I prefer Mark Williams but they cost more money.

    If you do a 9 inch Ford be sure to get a strong aftermarket third member case, and an aluminum pinion bearing retainer.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  3. #3
    Senior Member RACING JUNKIE lively's Avatar
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    THE 9" IS CHEAPER TO BUILD THEN A 12 BOLT/ THE 9" CAN CHANGE OUT GEARS ALOT QUICKER THEN A 12 BOLT----2 VERY STRONG POINTS FOR IT PLUS COMPARING A BUILT 12 BOLT TO A STOCK 9" IS NOT A TRUE COMPARISON ED ops: ops:[ APPLES TO APPLES AND ORANGES TO ORANGES]

    NO OFFENCE ED JUST MY FINDINGS OVER THE YEARS-- :wink: :wink: :wink: -DENNIS[LIVELY]

  4. #4
    Senior Member DYNO TECH
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    I agree with lively on this point. Dollar for dollar a 9 inch is the way to go especially if your talking relatively stock configuration. A 12 bolt traditionally takes less horsepower to turn but that's about where the advantages end. 9" is stronger, easier to work on ( I'd much rather have a third member on the bench setting up gears then rolling around on the floor or in the pits. I think also if your at the track and needed parts you'd be much better off with a 9". You also don't have to add c- clip eliminators like on a 12 bolt.

    I agree with Ed that you really either need a nodular iron or an aluminum thru-bolt case, and an aluminum pinion support. Somtimes the ring gear must be chamfered so it clears the pinion pilot bearing area.
    'A government big enough to give you everything you want, is big enough to take away everything you have.'

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  5. #5
    Senior Member DYNO OPERATOR
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    Of course you guys are right. In my opinion a stock 12 bolt High Performace rear with the Hi Impact axles and Series 4 positaction is stronger than the standard bread and butter 9 inch. Factory rear ends the Dana 60 is the strongest and the cheapest as well as heaviest.

    I have seen so many guys put regular 9 inch fored rears with factory regular duty carriers and retainers and be disapponited because they had read the 9 inch is strong. The factory 12 bolt is at least as strong as factory run of the mill 9 inch and the Mopar 8 3/4 is worse.

    Guys without the finds to buy or to build a really tough 9 inch can install a factory Dana 60. They can also jst make the initial hit a little softer so it does not shock the rear end. For example launching on foot brake is easier on rear end.

    I have built Bullet Proof 9 inch rears but it is not cheap. You will never make a 12 bolt to be fully bullet proof.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  6. #6
    Senior Member DYNO TECH
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    If a guy can come up with a factory nodular iron case and upgrade to some Moser or MW 31 spline axles and spool you have a pretty darn tuff unit. I've run this same setup in a 3500 lb Super Street for many years and never an issue, also used the standard street gear instead of a pro gear. Same set of gears since 1990. This same setup was in the car in my avatar on that run and many more just like it.
    'A government big enough to give you everything you want, is big enough to take away everything you have.'

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  7. #7
    Senior Member RACING JUNKIE curtisreed's Avatar
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    I don't agree that a 9 inch is cheaper to build. You should probably change out the standard center section on your ordinary 9" so you would need aftermarket center section and pinion support, after that the bearings, axles, housing ends, spool, gears are not that much different in price.

    That said I think 33 spline is the largest you can put in a factory 12 bolt. I will say that in my experience it is easier when modifying 9" rears and as Brian said easier to work on. Ultimately the 9" can be made stronger. I wouldn't spend the money to change out the 12bolt in my roadster but if I were starting from scratch I would go with a 9" because of the options it presents and for resale value.

    Curtis

  8. #8
    Senior Member EXPERT BUILDER
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    stock 12 bolt a little stronger than stock 9"
    12 bolt can be beefed up cheaper than 9"
    both require gears, spool , axles, and housing ends, but 9" requires beefier center pot, also bracing and inside housing welding is a good idea.
    A dana 60 would be stronger than 12 bolt or 9" with comparable axles/spool/ gears.
    If money is no object, then fabricated 9" housing with all the goodies would be very strong, but would it be stronger than the dana?? dont know all the big boys use the fabricated 9" or those modular designed ones.

    Fabricated 9" look trick under the car, dana and 12 bolt it seems these days are passe'
    In my opinion a dana 60 with axles/spool/gears would give good service in almost any car running down to 7s, or quicker if the car is light.
    Ed

  9. #9
    Senior Member RACING JUNKIE
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    i did not want to answer this one because i figured if blaserman has
    been using 12 bolts for a while he should have first hand how strong
    they are, or can be. I have (acording to ed) the worse a mopar
    8 3/4 shortened with moser 35 spline axels w/a strange 35 spline
    spool with 4:56 us gears, back braced and plenty strong for me, but
    hotrod mag. had tested beefed up 12 bolt/9" and the 9" came out
    ahead, and whats the answer, what ever well beefed differential,
    and mopar is the worse, thanks.

  10. #10
    Senior Member RACING JUNKIE lively's Avatar
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    i have seen the 8 3/4 mopars in big horsepower cars that hold up very, very well!!!!---i prefer the 9" because i have proved them on several violent reacting cars and have very little problems if any-plus i drive my cars on the street and strip and can change the pumpkin out for the street gears quickly---THE FACTORY WAR CASE AND NODULAR CASES WILL TAKE ALOT OF HORSEPOWER WHEN THE GEARS ARE SET UP RIGHT-[ I HAVE HAD MORE TROUBLE WITH THE U-JOINTS THEN ANYTHING ELSE]--BUT THEN I AM A FORD FREAK :lol: :lol: :lol: ---LIVELY


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