94 Limited w/ABS can't R&R master cylinder???

[Turford71]

I have a 94 explorer limited 4WD, stock, no mods, never really had an issue until now. Need to replace master cylinder, there are lines going to ABS servo/motor. Any way possible to install my new master cylinder without causing further headache. I used to be a mechanic before all the new mumbo-jumbo gaggets. Any help would be greatly appreciated. I'm pressed for time otherwise I would continue to browse this site and will when I stop my vehicle in a safe manner. sandypantsct@gmail.com

 

[trashtruck]

Do a good bench bleed for the master cylinder and bleed the air from the line just before the abs module. After that it should be just a normal bleed. Keep the fluid full till you are done.

 

[Turford71]

M?m?m?m?

I'm not sure i understand how that process keeps air from getting into abs system when you put the lines back on master you will get a little air in the lines, moving forward to bleed air from the lines we pump the brake pedal open bleeder valve air is released, hold pedal down tighten bleeder valve and continue....understood. my issue is when your pumping the brakes to do the bleed that little bit of air could already be in the abs module. I want to avoid that at all cost.

 

[arco777]

Last time I did the job, here is my conclusion.

Before replacing the M/C, unplug the ABS relays and fuses. During the job, if you don't let the ABS pump power up, you won't get air in it. If you powered up the pump during the job (i.e. turn key to RUN, ABS self tests) then the pump and valves could have admitted air in. Otherwise you should be okay.

Perhaps since the M/C is above the ABS pump, gravity took care of any air bubbles in the lines running to the pump. If I'd let the ABS pump power up, it could have "burped" and admitted air.

After my M/C replacement, I left the ABS system unpowered for about a week and drove the vehicle normally without issue. Then I plugged all the relays/fuses back in, checked ABS operation doing panic stops on gravel, and I never had any trouble.