Power steering problem

I have just replaced the steering box on my 1993 discovery, but I can't get the power steering to work. I have spent the last 2 hours trying to bleed it, but it is just not happening. I open the bleed nipple on top of the box and turn the steering full to the right, and fluid comes out just fine. I turn it full to the left with the nipple open, and nothing comes out of the nipple, it also sounds as if it is sucking air through the nipple. can anyone offer any ideas as to what is wrong please? I have done a search on here, but not found anything useful.

The system should not need to be bled,it will self adjust by turning to each lock as it has a return pipe.The book says that you shouldnt keep it at full lock for more than 10 secs at a time.Try that first,obviously making sure that you have a full res,topped up as the system fills.Then if that doesnt work....ask James Martin ! Thats what I always do !!

Seriously though,try that before you start thinking on seals etc.

Lift your front end up on stands or a lift. Take the cap off your res, make sure it is filled then go from lock to lock for a while holding it, banging it into the stops, etc..... give it some rough handling. Keep checking the fluid level though. You might find where the pump is cavitating with the air, your res looks like it is full of blamange but it'll settle down after a while.

I never use bleed nipples as they're more trouble than they're worth! Especially if they shear off or don't seal up properly.

Check the pump. Shaft on mine broke inside so looked ok till I took it off as it then fell apart. easy fix put new one in took less than an hour.

So long as those 10mm head M8s that are soft as butter dont round off

remove pressure pipe from box one from pump to box and put end in clean container see if pumps working ,as said they will bleed themselves

Did my 300 tdi y'day-wouldn't bleed from the nipple on undoing,so took nipple out-fluid poured out -nipple was blocked with rust-cleaned nipple-worked fine.
Only problem is,I bought this pump in readiness(trying to keep one step ahead of the disco-lol) a couple of months ago,and it is britpart-not sure how long it will last