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K. Wiggins
K. Wiggins, ASE Certified Technician
Category: Car
Satisfied Customers: 3001
Experience:  ASE Certified Technician, Associates Degree in Automotive Technology, 15+ years in the trade
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You answered my question and I bought a new master brake cylinder...Ho

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You answered my question and I bought a new master brake cylinder...However, my mechanic thought it might be the master but as I looked and felt under the hood, when my dash light said, " brake- (P) (1)" and under that, check brake.....After I run the engine a couple of minutes, a "Hum" sound is emitting...the light is on, but after a minute or two, stepping on the brake pad, the light goes off but the humming continues.....I looked under the hood and pressed my fingers onto the "hose" connecting to the round cylinder attached to the master cylinder and it vibrated every few seconds, even with the light off....humming away......question.....does the warning "(P) (1) refer to the powere pump?
The humming is the abs motor. it should not be humming constantly without the brake off. Usually when this occurs it's due to a faulty accumulator. There is a switch that measures the pressure and will trip the warning light you see. If you have the used unit I would go ahead and swap it out. Click here for the test your mechanic can perform to confirm an internal leak in the accumulator/pump.
If you're driving the vehicle be cautious. It is possible for the brakes to lose the power boost and become very hard.
If the test does not show leakage let me know and I can advise further.
Customer: replied 4 years ago.

You said, "IF you have the used unit I would go ahead and swap it out"


I think the unit is the original one....sounds like I should "swap it out" anyway, it's so old...

If I buy the part......what is it called? so I could go to car as suggested by the former tech...

It should be listed as ABS pump or hydraulic control assembly. They may be a little pricey even used (100-400) internal leaks in this unit are very common even when they aren't as old as your current one. Plymouth had it's fair share of issues with this type of system and only used it a few years. If you have trouble locating one let me know and I will do my best to assist you further.
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