New to the site . I hope I can help as much as I know you will help me.

Have a axle seal leak so I pulled the axle and I notice that there is excess thrust on the axle , so pull the other side axle and look at the center section and I see that both pins are completely gone (741) case, so I am thinking that is why i have so much thrust on my axles , is this correct? So I have a 489 case that I can slip right in, Now on the 489 case it's a close end where the axles slip in no pins with that said how does the thrust nut adjust the thrust on both axles? THANKS

Alan welcome aboard. If the 741 is a sure grip it would have 2 "buttons" held in tight with a roll pin. A non sure grip would only have the flat surfaces on each side that the axle end butt up against. I'd pull the pig & retrieve em if it was a SG. when done you would bolt the axles in & adj the pass side one till you have ~.010" end play on the pass side. I would replace the seal (measure the depth of the old one & drive in the new one the same distance) & use a large an OD of round flat driver that you can to drive it in. put some sealer inside the housing at the location where the seal will end up. get the seal started square with some light taps then drive it home with as few moderately heavy blows as possible cuz every whack increases the chance of deforming the fragile seal. First pack the spring area on the back side of the seal with heavy grease or vaseline. when you drive in the seal to seated if it looks deformed (not flat) pull it & get another one (they're cheap), this ain't a job you want to repeat & for sure get a round flat driver a hair less OD than the seal OD. I like to raise the side I am working on a bit above horizontle just to keep fluid at the other end.

If you have had excess end play on your axles then there is a possibility that your axle bearings and seals could be damaged. I just replaced them on a customers car that had the pin break and buttons fall out. I recommend just fixing the buttons with a new pin because that 741 is probably a sure grip.

Yes the 741 is a SG .just seams odd they fell out, after removing both axles the driver side had the adjustment Nut for thrust adjustment,I will switch and put the adjustment on the correct side . And thanks for the Tips on installing the seal great info

Would the pin be a standard roll pin ?

the 489 I have is all so a SG . But no pins, so would the same thrust adjustment to this casting work also? Just would like to understand if any difference between the two with the thrust adjustment?

Mopar used two different types of posi units in 1969, the early Dana clutch type that used the center adjuster with the retaining pin and the other type that didn't use clutches inside of it and no center adjuster pins or retainers either. 1969 was the first year for the 489 case also but not the last year for the 741 cases so the 741 posi could be either type depending which year they where made in
On the end play use the side adjuster to barely have any end play, no more than .010, less is better than a tiny bit to much

Thank you for the info on the difference between the 741 and the 489 SG , it helps me understand

The sure grip carriers are interchangeable from case to case. I have run a clutch sure grip for years without the roll pin. You just have to know that if you pull the axle the button will probably come out and fall into the housing and you will need to remove the center section to get it back. You can install the buttons into the center section through the axle tube. I have never found it that difficult. The 741 case is just as good as the 489 caee except you have very few new gear ratio choices and is better in that it doesn’t use a crush sleeve.