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.