Brake issue, pedal low

K

Knut

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Have vented brake system twice, pedal still low. Yesterday, I noticed that pushing the brake pedal at idle increases the rev's. Suspect the additonal air must be coming from the booster. Should I be looking for a new unit, or is there another cure? (D-jet, original booster)
 
Knut said:
Have vented brake system twice, pedal still low. Yesterday, I noticed that pushing the brake pedal at idle increases the rev's. Suspect the additonal air must be coming from the booster. Should I be looking for a new unit, or is there another cure? (D-jet, original booster)
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There may be a language issue here. I think you meant to say you bled the brakes. How did you accomplish this? Assistant pumping the brakes while you opened the bleeder screw? Or, did you pressure bleed the system by pressurizing the brake fluid reservoir?

Did you perform some brake maintenance prior to bleeding the brakes?

You could have a low pedal due to air in the system, or worn master cylinder or even worn calipers or old brake flex hoses (unlikely but possible).

Nothing lasts forever but I wouldn't jump to the conclusion that your booster is defective. You have a hose and a one way check valve that could be loose, leaking or defective. The booster has the master cylinder attached to it. There is an "o" ring that is between that connection. It could be leaking too.

The traditional test of a booster is to run engine so that the booster is activated by manifold vacuum. Then turn off engine. Pump brake pedal and notice the results. You should notice the pedal effort increase. After all, the booster is the primary component of "power assisted brakes." Pumping the brake pedal when the engine is idling will usually cause the idle to increase but maybe by 100 rpm or less.

hope that helps.
 
Your engine idle speed can also be the result of a vacuum leak on the back side of the booster, as the rod moves inwards as the brake pedal is applied.
If you need a good brake booster, I have several on the shelf that have been refinished during restorations, and not used as we changed brake systems and intake manifolds.
 
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