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Thread: muncie rock crusher

  1. #1
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    muncie rock crusher

    does anyone know anything about these gearboxs, like how tuff what there worth and are they any good??

    i'm thinking bout putting one in my vk and i just wanna know if there any good?

    thanks

  2. #2
    Non player character GTSBoy's Avatar
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    Rock Crusher was the M21 gearbox I think (hearking back to my old old old Street Machine reading days!!!). If not then it is something even stronger.

    The M21 is plenty strong enough for a fairly worked NA 308. Let's face it, for many years there were no alternatives.

    But why would you want one now? You don't want a 4 spd do you? There are plenty of strong 5 speed gearboxes out there.

    cheers
    Quote Originally Posted by bugle View Post
    The non GTS's were gay

  3. #3
    Opens LJ38L's Avatar
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    Hope this helps

    The Muncie 4-speed box was used with many different Holden models and engine combinations from 1963 through 1974. The basic design and operation theory of the gearbox changed little during this period, however several design upgrades and modifications were made during the total production run. The Muncie was used with most performance engines, and is not to be confused with the Saginaw or Borg Warner 4-speeds.
    The Muncie is distinguished from the Saginaw in that the reverse lever on the Muncie is mounted in the extension housing, where the Saginaw reverse lever is mounted in the side cover. The main difference between the Muncie and the Borg-Warner is that the Muncie has a 7-bolt side cover and the Borg Warner has a 9-bolt side cover.


    Muncie 4-speeds were produced in two different ratios wide ratio (M-20) and close-ratio (M-21). An extra heavy duty close-ratio version (M-22) was also offered on many of the big-block high-performance models.The choice of transmission was dictated by the engine size and rear-axle ratio. Axle ratios of 3.73 and lower (numerically higher) came with close-ratio transmissions, while axle ratios of 3.55 and higher (numerically lower) used wide-ratio transmissions. In addition, many GM high-performance engines came with M-22 “Rock-Crusher” in the 1970-73 years, however an early version of the M-22 was available as early as 1965 in Corvettes.

    Proper identification of the transmission type is absolutely necessary, but sometimes difficult due to several factors. First, GM used several different methods to label and identify transmissions from year to year and model to model. Unfortunately the identification systems seem to have many exceptions, rendering them virtually useless to the restorer. In addition, due to engine and transmission swaps, and modifications that occur over the years many cars do not carry the original drivetrain that they were produced with.


    M-22 “Rock Crusher” Identification
    The M-22 close-ratio transmission is easily identified internally from the M-20 and M-21 versions by the angle of the gear teeth.

    The M-22 was only produced in a close-ratio version, so it will not appear on models with high rear-axle ratios (3.55 or lower numerically) unless someone has changed it.

    The main internal differences in the 3 types of transmissions are listed in the parts below.
    • M-20 differs from M-21: Input shaft and Cluster gear
    • M-20 & M-21 differ from M-22: Input shaft, Cluster gear, First, Second, Third, Reverse idler gear

  4. #4
    Farty and bloated Hqcoupe350's Avatar
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    I think there were two strong versions of the Muncie 4 speed. The M22 rock crusher and the Super T10 which was based on the M21?

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    from what ive found so far,there the factory box out of the old big block corvettes and the like. i stumbled across a hotrodders forum from the U.S. and read some old threads and they say that there tuff as anything! they reckon over 600hp to break them.they also say that the diff ratio needs to be really low as the box's gears are very tall (but close ratio)

    so i just bought one and a nice new vertical(?) gate shifter too

    thanks for your help fellas

  6. #6
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    The M22 rock crusher was not installed in holdens. The only muncie that i am aware of being factory fitted in a holden is the M21 in the 350 HQ.

    The M22 is very rare and desirable. It is nearly straight cut, and as a consequence, is noisy!

    The muncie M21 is american made. The M21 designation was also pinched by holden for the aust 4 speed which is a completely different box.

    The T10/Super T10 are different again, made by borg warner.

  7. #7
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    do you know how much there worth?

    i have allready bought this one. just wanna see how i did

  8. #8
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    If you were in the states, it would be worth a lot. Restorers pay big dollars for them because they are used in rare big block L88 corvettes and camaros and the like, which can be worth several hundred thousand $US. Even the date code on it can have a huge effect on it's price and desirability.

    In Australia people usually opt for a cheaper top loader which is equally as strong.

    Are you sure it is a M22, and not an M21?

  9. #9
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    have to double check but i bought it from a good source. the cash gets handed over on monday,so i'll double check before then.

    if it is what should i pay?

  10. #10
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    I had a rock crusher in the old HK350
    It was a pig to drive
    Decel was a pain in the arse as the synchros were abit ordinary but upshifting was fun. Remember to be "firm" with it.i think rebuild parts are getting pricy too.
    Location Perth Western Australia

  11. #11
    Avatar by Southo ROTATR's Avatar
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    Seeing as u bought it off Frenchie u got ripped

  12. #12
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    haha havent bought it yet. just wanna know if its the real thing!

    dont tell him i want it or the price will go up.

    ohh.and i used to getting ripped off.
    Last edited by hsv_wagon; 23-02-03 at 07:43 AM.

  13. #13
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    Nothing will be lost if it's "only" a M21 - providing you only pay a M21 price. The M21 will more than likely be better suited to your application anyway.

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    i want something pretty tough though. i have little mechanical sympathy if any and the motor is expected to make around 450hp... (crosses fingers)

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    Location Perth Western Australia

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