What is this on the back of my rally wheel?

[Mark E.]

This is on the backside of two rally wheels on my '70. It's soft enough to leave a mark when pressing with a screwdriver.

Has anyone seen this? Is this some sort of field repair? Or maybe undercoating that dripped onto the wheels somehow?

Screenshot 2021-03-15 173652.jpg

[Jimmy G.]

Re: What is this on the back of my rally wheel?

Paint I think Perhaps covering something. KH did not do show quailty paint jobs on the wheels they sold to GM. See if there is anything under it but I suspect not

[Mark F.]

Re: What is this on the back of my rally wheel?

This is on the backside of two rally wheels on my '70. It's soft enough to leave a mark when pressing with a screwdriver. Has anyone seen this? YES Is this some sort of field repair? NO Or maybe undercoating that dripped onto the wheels somehow? NO

Hi Mark,

In my day at another manufacturer of wheels, they were hung on a conveyor that traversed a "small parts" paint booth. The wheel was suspended on that conveyor at about chest-height with a hook thru the hub hole. As the unpainted wheel passed by the paint booth worker, he* would spin that wheel down (counterclockwise) on the hook with his left hand (if he was right-handed) while simultaneously pointing the spray gun at the rotating wheel; usually creating a fairly even coating of paint all the way around as the wheel spun freely on the hook.

More care for preventing runs such as these was taken on the front side than the back side...I think "more is better" on the back side was the mantra; so coverage could be excessive and run down to the static point once the wheel stopped spinning.

The conveyor then travelled thru a drying oven. The bubbles you show in your photo are most likely caused by the solvent-based paint back then rapidly volatilizing during the oven heating (essentially boiling off) causing the cratering shown in your photo. I doubt you will see that in more than one area of the backs of your wheels...they were only painted once (sometimes heavily); so when they stopped spinning - the "defects" you see were almost always at the low point of the wheel where any excess paint flowed down to that point before it could be set up in the drying oven.

*PS - I'm not gender-unconscious, but I was in many paint booths in my time and it just happens I never encountered a female painter in the booths I was in...

[Mark E.]

Re: What is this on the back of my rally wheel?

Thanks Jimmy and Mark. And Mark, I appreciate the detailed first-hand explanation. I feel better that these are probably not repairs.