Question: Can anyone give a definitive answer as what makes the hydraulic pumps so noisy and is there a cure..my issue is....front pump is noisy when cold and continues to be so for 20 minutes or so..it will eventually quieten but its still audible...sometimes after a two minute turn off and restart it will start noisy again but soon quietens however never to the point where its silent..i have bled the system from the accumalator to the rear brakes with rr fluid and checked the pumps output which appears to be good.there are no leaks.however the adjoining sphere is weak but i don't get pressure lights ever while the engines running only after 10 pumps when turned off...again the question is what causes the noise that plagues most of these pumps?is it air? shim adjustment?old age?and what is the guaranteed cure to the annoying noise

shadow 1 1973 125,000 miles

Answer: Regarding the noise on the brake pumps, I would suggest that this means that your accumulators are low on pressure which in turn would make the brake pumps work harder.
This suggests that you would need to change the accumulators and the valve bodies.Possibly the brake pumps as well.
I hope this has given you a starting point
Many thanks.

Answer: Further to my previous here is a more in depth explanation:
We would agree that your diagnosis of low accumulator pressure is correct and we would recommend replacing both accumulator spheres and valve bodies (or at the very least resealing the valve bodies). You will need to remove the valves in order to replace the spheres.
Just to confirm that the hydraulic system is pressurised by the mechanical action of the camshaft on the brake pump push rods which physically pump the fluid from the brake pumps to the accumulator spheres. If the diaphragms in the spheres have perished then the spheres will not retain the nitrogen gas which pressurises the system.
If the low pressure warning lights come on after ten pumps of the pedal then the spheres need replacing – they should take about 40 pumps to depressurise the system and bring the lights on.
It may be that the pumps will also need replacing if they have been “over-worked” due to the low accumulator pressure. We would recommend removing them and checking the lift on the push rods – which should be approx. ¼”. Please be aware that the lobes on the camshaft for the brake pump push rods can wear so these should also be checked.