Flush­ing hy­draulics

Car Mechanics (UK) - - Steering Guide -

When­ever a ma­jor com­po­nent, such as a pump or rack, is re­placed, the hy­draulic sys­tem should be flushed with fresh fluid. This pre­vents pre­vi­ously cir­cu­lat­ing con­tam­i­nants, such as swarf, from short­en­ing the life of the re­place­ment part. Should the reser­voir have a fil­ter, it must be clean and un­blocked; in some cases, it can­not be cleaned and you will have to re­place the reser­voir.

Re­move the pump’s high-pres­sure pipe at the steer­ing rack end and place a suit­able re­cep­ta­cle on the floor to catch the fluid as you pour it into the reser­voir. When the colour of the fluid that runs from the pipe is of the same hue as that poured in, you know that the old, dirty fluid has been purged from that part of the sys­tem.

To flush the steer­ing rack, dis­con­nect the re­turn pipe from the rack to the reser­voir at the reser­voir end. Plug the reser­voir con­nec­tion so that fluid can­not es­cape and fill the reser­voir with fluid. With the front wheels raised and the en­gine off, turn the steer­ing wheel slowly from lock-tolock, en­sur­ing not only that the dis­placed fluid is col­lected but also that the reser­voir fluid level does not fall too low, al­low­ing air to be drawn into the sys­tem. With the ig­ni­tion, or fuel, sup­ply dis­abled (note that this could trig­ger a fault code on some ve­hi­cles), crank the en­gine over, en­sur­ing that it does not start. This floods the me­chan­i­cal pump with new fluid. On elec­tro-hy­draulic pumps, you may have to start the en­gine briefly. Re­con­nect the dis­con­nected pipes and carry out the fol­low­ing bleed­ing pro­ce­dure.

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