This one? 7/8"

 

That's the part but mine is bigger than 7/8" (My 1" wrench is too small). I noticed that your truck is an 84, whereas mine is a 90 would that be the difference?

 

Sorry, Don't know.

 

pipe wrench time

 

Just get all the sizes, one of them will fit!

 

well if 1" is too small then you cant be far from it cuz ive never seen a fitting on a water pump past 1 3/4". tajke a guess on what size it looked like and grab 3 sizes close to what you think

 

Yea, because buying individual sockets is cheap!
JK, I agree, thats what I'd do.

 

then buy a set of large sockets, always nice to have around anyway, lol.

 

Your "90 should have a serp. belt. water pump. The '84 is v-belt driven water pump. The serp water pumps have a bigger bypass inlet hole. Been a while since I had to take one out , 1 & 1/16", maybe 1 & 1/8" got oldtimers disease. HaHa.

 

There where only 3 sizes above 1", so I picked a 1 1/8 and that was the right size

Nipple is now off (got a wrench instead of a socket so I could "help" with a BFH)