Car Mechanics (UK) REPLACING THE HYDRAULIC PUMP
Replacing an engine-driven PAS pump is well-within a Diyer’s capabilities, provided that you keep the working area as clean as possible. Dissolve any oily grime from the pipe unions with brake cleaner, thus reducing the chance of contamination from entering the system when you disconnect the pipes. The following guidance is generic but it will give you the best idea about what you may encounter.
Prior to dismounting the pump, check that you do not need to swap over the pulley from your old unit. Many remanufactured pumps have a surcharge fee added, which is refunded when the remanufacturer receives your old pump in good order. 5
It might be easier to remove the pulley with the pump still installed. However, never use a chain wrench to hold the pulley stationary, or employ any other method that risks damaging the pump body, which will forgo your surcharge. 6 7
At best, a chain wrench will damage the pulley ribs, shortening belt life. Pictured (above right) is an extreme example of pulley damage that, obviously, dictates that a replacement one is sought. Pictured (right) is a puller design that should be used after removing the securing bolt(s).
Flexible pipes can perish, or leak from their ends. Should new replacements be unavailable, commission a manufacturer of high-pressure hydraulic pipes, who can make a one-off part, using your old pipe as a pattern. 3
Once you have removed the unions, protect the belt and alternator from escaping fluid and direct it into a suitable receptacle. Old PAS fluid should be discarded in the same way as old engine oil. 4
After cleaning the pipe unions, research if any O-rings, or single-use connectors (inset) are needed. Remove pipe brackets/ supports (arrowed), noting that any rubber/ plastic anti-vibration inserts are in good order and pipes are neither corroded, nor perished. 2
Identify your pump’s fixing method on the front-end auxiliary belt drive (FEAD). Note that removing some pumps dictate that some other components are removed first. Ensure you have the suitable tools that enable you to work in restricted spaces. 1
Inspect the removed pump carefully and research if you need to swap-over any internal parts to the replacement. This includes flow valves, or filters, such as those pictured. Clean any removed parts thoroughly with brake cleaner. 9 10
On some cars, you may have to remove the PAS pump’s bracket. Note how it is attached, prior to separating and transferring it over to the replacement pump. It is good practice to clean the bracket, once removed. 11
Due to this pump being particularly inaccessible, it was easier to unbolt it from the mountings to access and unscrew the unions. This demonstrates that pump removal methods differ according to your pump’s design and location.
Some engine-driven pumps include not only the pulley but also the reservoir and so check if the replacement pump includes those parts. All ports on remanufactured pumps are plugged, which you should remove as late as possible.
Remove any protective bungs from the pump and fit the pipe unions, taking care not to cross-thread the ports. Top-up the reservoir and check for leaks before, during and after you start the engine and again after work has finished. 16
Fit the complete pump to the engine block, locating the retaining bolts but not tightening them – yet. At this point, replace the drive belt and check the condition of the whole FEAD, including any tensioners. 13 15
If required, clean the flange and swap the pulley between the old and replacement pumps, ensuring that the bolts are tightened to their specified torque and that you damage neither the pulley, nor pump body, as you do so. 12
Fit the FEAD belt and ensure it is adjusted to the correct tension. PAS pumps that employ separate belts can have a manual adjustment facility, as arrowed. An over-tensioned belt will reduce the life of the pump bearings.
The system should be flushed and bled next.
Some pipes possess angled ports that can be made from plastic. If you twist and break the port when fitting a hose, it will not only leak fluid but also air will enter the pump, creating noise and reducing its working life considerably.