I've been doing quite a few automatic transmissions lately and was wondering what is a good method to paint the aluminum transmission case. I've seen some painted and they hold up and some the paint doesn't last. Just wondering what everyone else is doing?
Same goes for car paint the kind used on the top of the car.
Heat paint can hold up as well. But rattle can is only so good.
If your hot tanking the case then the case will be super clean at some point stop and paint it then before you go further. give the paint the best bite.
Im sure a trans specialist will jump in and help. But in my case i like to brush them with oil base its thick and stay where you put it even if the case is not perfectly clean. Which for me it never is. Tractor supply tractor paint.
I hot tank all the cases on the transmissions I rebuild. I did one for a buddy and he painted it with automotive paint and after a season (it was a circle track race car) it just peeled off. I tried Duplicator high temp cast aluminum on the last case, but won't know for a while if it will hold up.
Clean, clean, clean.... If you aren't going to scuff it for tooth shoot it with self-etching primer. Zinc-Chromate (made for aluminum) will work well also as a primer.
Mark
The case (aluminum) doesn't like to hold on to most paint. An etching primer and a clean case is a good way to get the paint to stick. The transmission gets hot so most light colors will darken over time. I used "Safety Yellow" on the C4s that I built and that color is fairly stable. I sprayed the clean case with vinegar and rinsed it before painting. then I covered all the openings in the assembled case and plugged my heat gun into the back of the transmission. When it got to 120F I shot it with the color. (acrylic enamel) and let it cure hard. With the case painted I took the case back apart and loaded the parts in it. When it was assembled it looked like each piece was painted individually because there was no paint on gaskets or bolts.
I agree here with old tech, Preparation is the most important part and cleanliness is #1. The method I use is after it has been scrubbed clean with soap and water, I take alumi-prep and scrub the surface with with it per the instructions. After rinsing again I coated the aluminum with Alodine 1001 clear and it received a final rinse. Then to the oven to heat the part and ensure all moisture is gone. I would then shoot a coat of Zinc Chromate primer followed by the paint. I think if I were to do any more I think I would try some SPI Epoxy Primer instead of the Zinc chromate.
Powder coat it before you assemble it or use an Oil based Alkyd Enamel (tractor enamel); adding hardener is a good idea, but you're still taking your chances without a proper substrate. We like our stuff nekkid. Maybe a powdercoat clear coat.
When I first started building transmissions they were never painted. I knew what was inside and the abuse it would take. One of my best customers came to get his transmission and asked why I didn't paint them... He explained that my customers don't get to see what's inside and that even well cleaned it looked pretty much the same as when they brought it in. To show the customers how meticulous I was on the inside I decided to paint the outside. I thought about the different colors available a lot of them were in use by other builders. I wanted a color that would show leaks, look good, and last. It just so happened that the safety yellow was on sale. It covered well and didn't discolor so I started using it. I have had complaints about the color and I have matched colors for some customers at their request and cost but most of my transmissions are safety yellow and there are a few of them out there.
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