Hard steering problem

Hello
I've got a strange problem with my '87 w201 2.0D. After 30-40 km a steering becomes hard, a steering wheel doesn't want to return to center automatically. When I stop the engine and
wait a few minutes everything returns to normal and works properly for another about 40 km.
I replaced the both lower ball joints and the idle arm bushing. There is not any play in steering and suspension.
Now I'm thinking of a power steering pump. It doesn't leak, but I can hear abnormal (in my opinion), ratteling sound from it.
What do you think? Maybe a steering box is cousing the problem?
Thank you,
regards
Maciej Wilk Poland
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It can be two things... but I'd replace them both... the power steering pump or your hoses ... With your hose swelling... constricting the flow of fluid... making it a hard to steer. which becomes like a manual steering...
But, I don't understand the part where it doesn't want to come to the center after turning... if it is really true, then I highly suspect your seals in the steering gearbox is bad.
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When you adjusted the steering box you did so too much and the box is locking up - dangerously.
That adjustment should be done in small steps - only 1/4 turn, then drive the car 10,000Km before making the next adjustment.
Try to adjust it back to what it was, it may be OK but maybe not and if not then it's damaged and will need to be rebuilt or replaced with a used steering box from a wreck.
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Ok, but I'm thinking in a bit different way. If the box is damaged, it will work improperly all the time, not only with warm fluid. Besides if I do short movements (about 10 centimetres in both directions) steering is ok. A "resistance" starts further.
Thank you for your help,
Regards
Maciej Wilk Poland
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