So why replace the BMW E24’s original belt driven Hydraulic pump for an electric one?
If you think of when you most require steering assistance, its usually during low speed manoeuvring like parking or pulling out of a T junction. Conversely, when driving quickly along A roads or the Motorway you hardly require the benefits of power steering, yet the power assistance hydraulic pump is running full bore, which of course is unnecessary sapping power from the engine. Whereas an electric hydraulic pump runs on standby until the extra assistance is called for, like when you turn the steering wheel to park.
Now with the BMW E24 6 series (and E28 5 Series) things are made a little more complicated by the use of the hydraulic power steering pump to provide assistance for the brakes too. Called Hydro-boost, BMW used this set up due to the distinct lack of space for a more traditional vacuum boost, where the vacuum is provided from the intake manifold. Instead the hydraulic pressure from the power assistance pump is routed to a booster attached to the brake master cylinder via a valve system which splits the hydraulic pressure between the steering and brakes, it also keeps the ‘bomb’ pressurised. This bomb is a pressurised vessel that gives emergency brake assistance should the pump fail (pump drive belt breaks or engine stops).
An electric pump setup should be more reliable and safer so long as there is power left in the battery there will be assistance and this of course is in addition to the bomb pressure vessel back up.
See how we did this conversion and the parts used here