I have a water pump leaking around the large nut on the pump shaft on my cat 30 it is a 1928 and I wanted to know whtat type of packing to use.

Where there is coolant then a treated type of packing is used. Cat might have it in a string type packing as I know it used to be available for things.Some pumps show a regular coiled type packing for some water pumps but I don,t have a parts book for a 30 but in the R2 book it shows the one for the shaft coming out to the fan blade as a 1A8742 and the rear packing nut next to the impeller main housing shows a 1A8736.Your going to have to take it apart to see what you have and maybe settle for the treated cord type that comes in a small roll.It is a black colored stuff that the cord is treated with.It might be graphite that it,s treated with but not sure.

thanks for the info I will take it apart and see.

Did you try adjusting the gland nut, tighten the nut a quarter turn and see if the leak stops, if not another quarter and so on, if the nut locks up before stopping the leak you will have to replace the packing.
AJ
Forgot to say that you tighten the nut in the direction the shaft turns

a graphite dusted cord (string) type also. I went to ACE Hardware one wekend and got some valve packing material. It works quite well, not leaking anti-freeze or water. I stumbled across a packet one time in a box of Auction treasure that had the real packing for water pumps. It was graphite impregnated leaded steel stringy stuff long and square which was rolled into a coil. When I investigated its use, it was deemed as being superior lasting to any sting or cord type material due to its shape and material make-up.
I don't remember what I put in the last 2 Ford Model A water pumps (string type maybe)? But I did get water-proof grease for water pumps to use.

Teflon string packing is real good also.
If you can't find it at the local hardware store, try a company that works on irrigation pumps, or domestic water wells.

i happen to have some graphite packing in stock but the nut is soo tight that i am having to let it soak with PB blaster for awhile to break it loose.

Thanks again for everyones input and advice.
It is great to have such a wonderful place to come to to share information about something we all love and have a passion for.
by the way i just picked up a 57 d4 today and i will post pics later.