I plan to go back in better weather and get more info, I didn't find an ID tag to learn the date of manufacture. Looking at the cab style I'd guess the 70s or maybe even early 80s. I wonder when they ceased production of this model?
We had one of these as a backup unit at a small rock quarry I managed here in Texas. This was back n 1980, and it was an old truck even back then.
I don't know much about these Mack rock trucks. However, there were several models built, and at one time they could be found scattered all over the US at rock quarries. They were more commonly seen in operations east of the Miss. River. Our old Mack was a M20X as I recall. The whole quarry truck series were "M" models I think.
Ours had a Mack engine. The one shown in this topic looks larger than ours. This one looks like it could be a 35 ton model, or thereabouts. The bigger Macks had tandem rear axles. I think they might have been 50 ton units. I am just speculating on a lot of this, based on what I heard way back in the 80's.
Back then, Euclid owned the quarry truck market. I guess Mack could not gain enough market share to continue the line. Cat was also making a big move into quarry trucks back then. That probably cut into Mack sales also.
I know one thing, those Mack quarry trucks were tough, tough, tough, and seemed to run nearly forever.