Today I bled the disgusting 10 year old brake fluid out of my dad's vehicle with a little pneumatic tool that sucks the fluid out nicely and started with rear right, rear left, front right, then front left making sure the reservoir was always topped up. I used dot 4 synthetic.

I test drove the car and it felt good. The braking felt smoother to me and overall just better. Then I had my dad test it and says 'dude you got air in the lines' and it feels too soft for him although the pedal never falls to the floor or even near it.

I recently had a commercial shop exchange the brake fluid on my wife's car and I've always noticed that brake pedal feels a little softer but with more braking control after a flush. To me that's better.

Could it be that my dad was just so used to crappy braking with 10 year old fluid and now it feels weird to him?

I can't see anyway that a pneumatic bleeder tool would be able to introduce any air into the system as it just sucks out one way.

  • Welcome to Motor Vehicle Maintenance & Repair! Jan 24, 2022 at 1:01
  • In what order does the car's service manual state to flush the lines? Is the braking system rated for DOT 4?
    – MonkeyZeus
    Jan 24, 2022 at 18:31
  • @MonkeyZeus I haven't checked the service manual as I don't have one. The abs system is in front of the car. Car is 2001 S430 Benz and it does take DOT 4.
    – VmroFan1
    Jan 25, 2022 at 1:17
  • @VmroFan1 My 2011 Accord says front driver, front pass, rear pass, rear driver. You should add you car model into your question because someone might know the details specific to your vehicle. Also, I've tried that crappy Harbor Freight pneumatic tool and ended up just doing it right by using a second person to pump the brakes.
    – MonkeyZeus
    Jan 25, 2022 at 13:26

1 Answer 1


I agree with your dad, there is air in the brake system. Bleed it properly and the pedal will firm up.

  • I thought that only if the pedal sinks to the floor that there is air in system? In my case it doesn't fall to floor or even near it. The braking action is good and reliable, the pedal only feels softer that what my dad was used to. We'll test the car more and look into taking any action, thanks.
    – VmroFan1
    Jan 25, 2022 at 1:16
  • 1
    A lot of air gives a lot of excess pedal travel, a little air gives a little. All it takes is a bubble or two and you get a "soft" pedal. Air compresses, brake fluid does not.
    – jwh20
    Jan 25, 2022 at 2:25

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