1. CM360

    CM360 Well-Known Member

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    My M has 7 1/4 rear. With a BB just going to the machine shop, I'd like to start with the rear suspension. Calvert parts and I want to go to a S60. Since I can get it shorter than stock length, any idea how short I can go to get a 10.5 or 11" slick under the wheelwell?
     
  2. 4speedjim

    4speedjim Well-Known Member

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    Relocate your leaf springs inboard. I think there's cheap kits you can get to go 3" without much effort. I think stock axle width is 59.2" wms to wms. "Drum to drum". Depending on what depth wheel offset you want to run narrow the axle to fit. A bodies are 55.7?". The 10.5" tires will fit.
     
    Last edited: Aug 7, 2018
  3. Oldiron440

    Oldiron440 Well-Known Member

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    How wide are the stock wheel houses and do you plan on doing a mini tubs?
     
  4. Oldiron440

    Oldiron440 Well-Known Member

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    One more thing do you have rims?
     
  5. Oldiron440

    Oldiron440 Well-Known Member

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    Basically you have to establish all the boundaries first, tire/wheel, wheel offset, spring location and wheel house width and location before determining axle width.
    Centering the wheel/tires in the wheel house or outer wheel house and spring on both sides will give you the distance. If your using disk breaks don't forget the thickness of the rotors in the width.
     
  6. BudW

    BudW Moderator Staff Member

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    A ’66-70 B-body Dana 60 is almost a direct bolt-in.
    The differences are:
    Perch width is 44.0” vs. 44.46” on FMJ (0.23” per side – little enough to push it in place)
    Propeller shaft length is roughly 3.38” shorter (from a 7¼” differential)
    ‘66-70 B-body (w/Dana) width (drum to drum) is 60.13”
    FMJ width (drum to drum) is 59.34”

    If you are getting a new differential made – then you can make it to your specifications ( perch width, drum to drum (or disk to disk) width, etc.). It costs almost as much to make a new Dana 60 than to find a used B-body one.

    The only thing I don’t like about the Dana 60 – is its weight. It is like comparing a boat anchor for a PWC (personal water craft) to that from an aircraft carrier.
    Other than weight (and its initial cost) – I don’t think there are anything else in the negatives column. Everything else are positives.
    An unspoken positive is it also helps with the front to rear weight bias.


    Note: original B-body differentials have Left hand thread lug studs – which can be a pain.
    Note: drum to drum (or disk to disk) refers to the wheel mounting surface (WMS, as mentioned above).
    Note: If using leaf springs – be sure to get the pinion snubber holes drilled. A B-body pinion snubber will fit and are still being repop’ed (I think).
    Note: Some disk brake setups might have a specific “width” to contend with (distance of WMS to leaf spring) – so you might to inquire about that, before finding out . . . too late.
    BudW
     
  7. Oldiron440

    Oldiron440 Well-Known Member

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    Some disk brake rotor hats are thicker than drums forcing wheels out farther than a drum brake setup would. In a tight setup the extra 1/2 inch might make all the difference.
     
  8. jasperjacko

    jasperjacko Well-Known Member

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    plenty of room for 10.5- 11
     
  9. Duke5A

    Duke5A Well-Known Member

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    An 8.75" rear from a 66-70 B body will allow you to run Mickey ET Streets measuring 275-60-15 without any rubbing issues. Can't remember the rim measurements though. Ran this setup at the drag strip a few weeks back.
     
  10. BudW

    BudW Moderator Staff Member

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    I need to clarify a tad. Not all (stock) ‘65-70 B-body 8¾” differentials are the same width.

    I don’t have (I did have but corrupted file ate some of my data) the Drum to Drum distance (or the Wheel Mounting Surface / WMS) spec’s.
    What I do have is the factory published “Tread data” which is center of (rear) tire to center of (rear) tire (which isn’t much to go on) and the flange to flange data (without backing plates or axles) measurement"
    ‘65-67 are 54.250” Flange to Flange
    ’68-69 are 54.936” Flange to Flange (0.686" wider or 11/32" wider per side)
    ’70 is 54.906” Flange to Flange (0.656" wider or 21/64" wider per side - than the '65-67 version)

    The Dana 60’s is similar:
    ‘66-67 are 54.250” Flange to Flange
    ’68-70 are 54.937” Flange to Flange
    Note: all of the above data is B-body's only.
    BudW
     
  11. Oldiron440

    Oldiron440 Well-Known Member

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    I was going to let it slide but a half inch an come handy. Those were hard to find in a 8 3/4 25 - 30 years ago.
     
  12. Locomotion

    Locomotion Well-Known Member

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    Is this for race only? (I know where there is a slightly narrowed B-body 8 3/4 with Moser 35 spline axles & other stuff. ;) ) But a Dana 60 might be better for big block/slicks/race only.

    When fitting wheels & tires in my Aspen wagon, I had to get a big hammer to "readjust" the front inner sides of the wheelwells. This was while trying to tuck in 9" slicks on 10" wheels to avoid too much sidewall sticking out. Don't know if other FMJ body styles are any different. If you have something to mock it up with, even if it's not the same size, putting wheels & tires in place under the car can give you a better perspective of clearances and what's possible.

    A Dana 60 may weigh more, but they are more efficient than an 8 3/4" - less HP to turn. I've heard of several race applications where the change made minimal or no difference in ET, especially when the overall weight of the car was brought back to the same weight.
     
  13. Oldiron440

    Oldiron440 Well-Known Member

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    The Dana has more parasitic power loss than the 8.75 but it is a minimal difference.
     
  14. Locomotion

    Locomotion Well-Known Member

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    I have to disagree. There was a magazine article many years ago that did a differential comparison. Chevy 12 bolt was at the top (Don't recall 10 bolt in it.) Dana 60 was near the top, above an 8 3/4" and Ford 9" was the worst. Despite bearing sizes being bigger in some cases, the biggest factor was the pinion being closer to the centerline of the ring gear made a differential more efficient. Basically, the pinion placement overcomes the inefficiency of bigger bearings and extra weight of some parts. Differences weren't big, but worthwhile nonetheless. Minimal or no loss in ET has been proven by several Stock racers going from an 8 3/4 to a Dana 60 and has been discussed on classracer.com

    On a side note, Going to a spool from a Sure-Grip helps more in the same comparison because of the bigger mass in a Dana 60 to start with.

    The ability to swap gears and less weight nice to have. But the extra weight of a Dana 60 isn't a factor and you don't have to worry as much about the life of the ring & pinion. I wish I knew who did that article. I think it was from the '70's or early '80's.
     
    Last edited: Aug 23, 2018
  15. BudW

    BudW Moderator Staff Member

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    I have only seen 1 broken Dana 60 before. 35+ years ago, a rather large guy came in to shop, dragging his Hemi car in. He pulled out of the trunk, a mangled propeller shaft that still had the front half of a Dana 60 and rear half of a A833 still attached to it.
    No mention about what happened (and he was big enough that no one in shop was going to ask any questions).


    Other than small differences – I do not see how there would be much efficiency difference between the 8¾” vs. Dana. I won’t get into an argument about it (I have 0 facts to agree or disagree).
    That said, I do hear a lot more from racing circles, the 8¾” does flex a lot more (under stress) and people are having a lot more breakage with the 8¾” in high HP cars.

    If I was racing full time, the Dana 60 is the only way to go (and can still be made brand-new to custom order).
    For my needs, the 8¾” will work fine (even though I’ll have big block(s), I don’t plan on high HP or high RPM).
    BudW
     
  16. volare 77

    volare 77 Well-Known Member

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    Years ago a friend had a stock oem Dana 60 in his BB Camaro. He raced the car and it went mid 10`s. He broke a axle about every three weeks. He was getting new oem axles from the local dodge dealer. After he switched to aftermarket axles he had no more issues.
     
  17. Oldiron440

    Oldiron440 Well-Known Member

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    I think the table is upside down the Chevy was most efficient and the Ford 8.8 witch is stronger than the Chevy then the Mopar 8.75 witch in stock form is stronger than the 9" Ford and then the Dana. There for a while they were selling 12 bolt centers for 9" Ford axles.
    Now recently I read that all it's all a bunch of wasted fret and the difference is so minimal that reliability should be the consideration.
    I remember the article in the magazine and I've plenty of busted 9", 8.75s and Danas. It all depends on how there set up and how there used.
     
  18. Oldiron440

    Oldiron440 Well-Known Member

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    One thing to consider is using a 727 and anything over 550 horsepower you have a bomb under your feet asppesally after a ring gear failure! A transmission blanket is a minimal defence and should be a requirement for all automatic cars on the track, I'd say put one on your hot street car.
     
  19. BudW

    BudW Moderator Staff Member

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    I’ve heard from my racer friends that aftermarket axles are stronger than OE or factory axles are (but are also more expensive).

    Correction, after a low gear sprag (one-way clutch) failure. The high HP engines (mainly big block), if that low gear sprag goes, it looks like a hand grenade went off inside (and outside) of the transmission.
    A blanket is a whole lot cheaper than getting metal/plastic feet/legs fitted.
    BudW
     
  20. Oldiron440

    Oldiron440 Well-Known Member

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    It happens just after a rear gear failure sometimes on the same pass.