Choosing material for a shift fork

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  1. #1
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    Default Choosing material for a shift fork

    Hi everyone,
    I was contracted by a transmission rebuilder to design and make some shift forks.
    They are discontinued and no longer available from the OEM manufacturer.
    Someone was making them from 7075-T6 and hardcoat anodizing but these forks are not a priority and causing shipping delays to the rebuilder.

    The rebuilder says "the stock ones are great, until they aren't." He adds that the billet 7075-T6 ones are "only good for ~10k miles before they wear out." He said he would send me samples I could see what "wear out" meant. I can say that stock ones have a halo where the slider rubbed on the fork. That makes me think it's more an alignment issue up and down along the fork rail but until I see the samples, I'm only speculating.

    My brain goes two ways here:
    1. People now believe their transmissions are bullet proof and hard shift, causing premature wear.
    2. What are the differences between a stock cast and a billet fork?

    The builder believes a honed cross hatch (similar to a cylinder wall bore) will retain oil on the friction faces of the shift fork. I am skeptical.

    So I looked up what the casting material on the original patent...
    Conventionally, ADC12 was chiefly used as a diecasting material in aluminum diecasting. Recently, high silicon aluminum diecasting materials with superior wear-resistant properties to those of ADC12 have also come into use. Such materials are used to mold the fork main body and the engaging part in a one-piece construction so as to decrease costs and achieve a lightweight construction.
    So I looked up ADC12. It's an aluminum alloy that is high in silicon. That makes sense, they need it to release from the die after it's cast. Does the silicon assist in lubricity against a steel slider? Is that why the stock cast forks last longer than the billet 7075?

    https://www.dynacast.com/en/knowledg...lloy-383-adc12
    ADC12 is 9.5-11% silicon

    Not only is a high silicone alloy being used, the original patent states:
    As shown in FIG. 5, a claw-shaped engaging part 52 is usually molded integrally at the tip of a fork main body 51, and the engaging part 52 slides on a rotating coupling sleeve 54. In order to obtain high wear-resistant properties in the engaging part of high silicon aluminum shift forks, a casting surface is cut by 50 ?m or more so as to cause pro-eutectic silicon to form on the surface.
    Ok. I can cut a 50 um, no problem.

    So I searched for high silicon aluminum alloys and came back with silumin, which is 16-19% silicon.
    https://en.wikipedia.org/wiki/Silumin
    and comparable to a 3 or 4xxx series.

    I started following the flow chart here:
    How and why alloying elements are added to aluminum

    ...and this page declares 5052 is the strongest:
    Magnesium (Mg) 5xxx - The addition of magnesium to aluminum increases strength through solid solution strengthening and improves their strain hardening ability. These alloys are the highest strength nonheat-treatable aluminum alloys and are, therefore, used extensively for structural applications.
    I can get 5052 plate cut to the size I need, and the price is similar to that of 7075-T6. I started talking to an old machinist about it and he said 5052 is the softest stuff he ever worked with. So why is this page saying the strongest?
    Why did the competition make forks from 7075? Why do other aftermarket shift forks use 7075 instead of 5052?

    We kicked around the idea of a steel shift fork but both the builder and I are worried about premature wear to the slider. I'm at a loss for what material to use and my head is spinning from all this data.

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  2. #2
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    Default Re: Choosing material for a shift fork

    You might want to give 2024 a brief lookover. ( https://asm.matweb.com/search/Specif...snum=MA2024T86 ).



  3. #3

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    What is the gearbox/transmission being used for.


    Quote Originally Posted by Paraquat View Post
    Hi everyone,
    I was contracted by a transmission rebuilder to design and make some shift forks.
    They are discontinued and no longer available from the OEM manufacturer.
    Someone was making them from 7075-T6 and hardcoat anodizing but these forks are not a priority and causing shipping delays to the rebuilder.

    The rebuilder says "the stock ones are great, until they aren't." He adds that the billet 7075-T6 ones are "only good for ~10k miles before they wear out." He said he would send me samples I could see what "wear out" meant. I can say that stock ones have a halo where the slider rubbed on the fork. That makes me think it's more an alignment issue up and down along the fork rail but until I see the samples, I'm only speculating.

    My brain goes two ways here:
    1. People now believe their transmissions are bullet proof and hard shift, causing premature wear.
    2. What are the differences between a stock cast and a billet fork?

    The builder believes a honed cross hatch (similar to a cylinder wall bore) will retain oil on the friction faces of the shift fork. I am skeptical.

    So I looked up what the casting material on the original patent...


    So I looked up ADC12. It's an aluminum alloy that is high in silicon. That makes sense, they need it to release from the die after it's cast. Does the silicon assist in lubricity against a steel slider? Is that why the stock cast forks last longer than the billet 7075?

    https://www.dynacast.com/en/knowledg...lloy-383-adc12
    ADC12 is 9.5-11% silicon

    Not only is a high silicone alloy being used, the original patent states:


    Ok. I can cut a 50 um, no problem.

    So I searched for high silicon aluminum alloys and came back with silumin, which is 16-19% silicon.
    https://en.wikipedia.org/wiki/Silumin
    and comparable to a 3 or 4xxx series.

    I started following the flow chart here:
    How and why alloying elements are added to aluminum

    ...and this page declares 5052 is the strongest:


    I can get 5052 plate cut to the size I need, and the price is similar to that of 7075-T6. I started talking to an old machinist about it and he said 5052 is the softest stuff he ever worked with. So why is this page saying the strongest?
    Why did the competition make forks from 7075? Why do other aftermarket shift forks use 7075 instead of 5052?

    We kicked around the idea of a steel shift fork but both the builder and I are worried about premature wear to the slider. I'm at a loss for what material to use and my head is spinning from all this data.




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    Default Re: Choosing material for a shift fork

    Quote Originally Posted by pfp View Post
    What is the gearbox/transmission being used for.
    I'd say it's going to be used equally for 1/4 mile drag racing as it will daily driving. I understand if the fork is getting beat up then the syncho hasn't slowed down the gear enough before trying to force the slider over the dogs, but tell that to people who can't drive.

    I still haven't received the samples from the builder.



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    Default Re: Choosing material for a shift fork

    Hi ,
    I used to work for a manufacturer of truck transmissions and we made shift forks from 1045 steel forgings and induction heated and quenched ihe pads only to withstand wear . I apologize if this is useless info to you .

    Ernie



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Choosing material for a shift fork

Choosing material for a shift fork