bobby-babylon

I have a 2002 4WD 4Runner Sport Edition. I've recently begun to notice a noise and feel a slight vibration in my brake pedal when I start my truck. The noise continues for 5 to 10 seconds until there is audible click sound. The sound reappears when I use my breaks a lot and it can be replicated when I'm not moving if I just pump my brake pedal several times which leads me to beileve it may be an issue with the master cylinder. My brake response and pedal travel also appears to vary from time to time.

I upgraded to the 199mm Tundra calipers and rotors about a year ago but the problem only began about 2 months ago. Has anyone had similar issues or any idea what the problem might be? Thanks.

MadCityRich

What you are hearing is normal. The 2001 and 2002 4Runners have a hydraulic brake booster instead of a vacuum based brake booster. When the pressure in the booster goes below a certain point, a pump turns on to boost the pressure back up.

It might be worth bleeding your brakes to make sure you don't have low pressure. If your brakes need bleeding, the air in the lines would potentially increase the cycling on the booster pump and might be what's leading to your variable braking.

I also have the 199mm Tundra front brakes on my 2002 4Runner and noticed more pump cycling and variable brakes before I had the dealership bleed the brakes. The hydraulic system makes bleeding a little more technical than standard vacuum booster systems. I'm generally able to get it 90 percent done, but for some reason I'm not getting it quite to 100 percent.

MadCityRich

bobby-babylon

Thanks MadCityRich. I'll give it a try and report back.