D 318 water pump diagram

I'm pretty sure the bellows seal assembly is pressed into the water pump housing and does not seal or even fit closely around the shaft.

The bellows must be compressed slightly (I would guess about 3/32") by the impeller as it is installed onto the shaft. The impeller seals the shaft by its taper fit and the washer and nut that retains it.

I expect there are some mismatched parts that are not giving the correct compression of the bellows, but if that is not the case, seems like I have had to glue the carbon ring to the bellows to get one to seal. The carbon ring is retained in the brass cup by several tabs which are bent inward to contact the edge of the ring. These can be carefully straightened to allow the bellows to expand and the ring to be removed if it is detached from the rubber.

Any adhesive used should be used sparingly and only applied to clean dry surfaces. I think I used RTV silicon gasket maker on one, though there are probably better adhesives available. The joint is not under much strain while in use..... I think CAT may have supplied the bellows and the ring as separate parts but the parts and service manual are less than clear on this. There is no mention of adhesive use to install the parts, but if it isn't sealing, I would certainly glue a detached carbon ring to the bellows.

Another trick I used on one is to bend the retaining tabs outward slightly more than they were originally to allow the bellows to expand a little more and get the carbon to contact the impeller hub or ceramic seal. This was using an impeller which had to be cleaned up in a lathe to restore the seating surface where the carbon touches.

Good luck!

Sealing points are the impeller shaft fit, housing press fit and the carbon ring to impeller fit. I suspect your impeller sealing flange is worn beyond the range of the bellow seal capability.
One of the later impellers with ceramic face would make a good recovery.

Thanks for the help.
Today I got a new bellows seal from Cat and it fixed the problem!

Thanks for the feedback. Was the one you got in the original kit defective or did it get buggered up?

It appears that the one in the kit from Regal was the old style
And the one I got from Cat was the updated one for the newer
Impeller. They looked just a little different on the sealing area.
Thanks alot glad to get it back up and running
I dont like running a newer hydraulic machine!!