Wayne
MikeStem will jump in and know how it is designed, when he checks in.
Michael is the Midwest expert on Fire pumps.

Also, welcome to the Stovebolt group.
As you can see, in just an hour and a half, you are already getting replies.

I'm with 3B on some kind of spline setup and you may have to unbolt the pump to slide foreward to disingage the spline.

Get as many numbers and the brand of pump you can, to be ready for Mike's questions.
Keep us posted and post pics!

Don King

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!