I have a 1979 3500 SD1 (UK spec,I have been the second owner for 20 years )which has developed loss of power steering.With the front wheels off the ground there is a lot of resistance lock to lock.
With the engine running and the pump rotating it makes no difference,the ball joints are fairly new.I have taken the pump off and all looks normal .The worse thing is I have promised my Uncle use the car while he is on holiday visiting from the UK so I have 2 weeks to fix it.

Any advise most welcome
Kind Regards Dan

If the steering is still heavy with no weight on the front wheels then my guess would unfortunately be the rack

Thanks Julian,I have stripped the pump down and all looks fine,seems like the rack .
Regards Dan

I'm assuming there's oil in it? I know it sounds obvious

System is pressurising?

Pump might be spinning but maybe isn't working, is there a pressure reflief valve open? Might be worth cracking open the HP pipe and see, beware of ratting machinery though!!!

Could there be a restriction in the pressure pipe?

Hope the suggestions are useful

I was thinking that even with the engine off, with the car jacked up the steering should be very light. If it's not then something's wrong and it can't be pump related because that isn't running.

That's my rationale anyway