2003 Brakes / Master Cylinder Question

09-19-2010, 07:15 PM
Hi Crew

I gotta question about my 2003 4Runners brakes & Master Cylinder.

I had my Toyota Dealership replace all pads and rotors in the 4Runner a couple months ago, and they bled the lines as well. About 6 months ago i had the calipers in the front replaced due to the ol' "frozen cylinder" sickness 4Runners are known for.

ive never been impressed with the truck's brakes as long as i can remember. You dont have to puch the pedal to the floor to stop, but you dont exactly stop when you touch the pedal.

I notice that when i start the vehicle, or even just throw it in park and pump the brakes, after 3-4 pumps i hear a compressor-like hum, as if the pressure is being increased. I know theres a booster on this unit, but I just odnt know to what extent it should be working. Should it be doin it THAT often? after 3-4 full pumps of the brakes?

Basically I wanna know if im looking at a new master cylinder or if its normal operation.


09-28-2010, 07:53 PM
The brake MC is an integral part of the ABS and IIRC, the VSC system.
What you may be hearing is the brake booster pump assy.
I'm not familiar enough with that system to know if your problem is normal.
But I do know that if it is a bad MC, you're looking at a large sum of $. :(

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