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Q: when bleed the abs unit on my |986 mersedes 300diesel it should come brake fuel out om the top of the unit

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ok I pump the brake whith the key on the hol the pedal dawn but no flued coming out of the bleeding screw on the top of the abs unit why .
My car has an automatic transmission.

ABS equipped vehicles have complex piston, cylinder, and valving arrangements. As a consequence, typically a bi-directional scan tool has to be used to expel air and/or bleed the system. Bi-directional tools remotely actuate the ABS system, using commands, to accomplish the bleeding. Inasmuch as your vehicle is 1986 vintage, there could be an alternate, "low tech" means to bleed the ABS system which is specified in the Factory Service Manual (FSM) and that a responding certified Mechanic would employ. ABS systems work under very high pressure and if you do not have the FSM, be careful experimenting with bleeding techniques as fluid could come out unexpectedly under high pressure. If you do not have the FSM and/or a scan tool, what I would suggest in your circumstances is a brake inspection which can be set up via YourMechanic’s website.

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