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I was hoping for some insight and opinions on the following brake issue I am having:
2007 Altima, ~58,000 miles
The symptoms are as follows:
1) When the brake pedal is initially depressed (during a normal stop), normal braking seems to occur.
2) If at any time after the pedal is initially depressed, pedal pressure is even slightly lessened (50% pedal travel let's say, back to 40%), a knock or kick is noticed against the pedal (pushing back slightly against the foot pressure)
3) Subsequently, if the pedal is not fully released, but is depressed again (40% back to 50% for example), the brakes grab very hard and braking is 2-3 times more forceful than normal as the pedal is depressed.
4) Releasing the pedal all the way restores the brakes to normal (with the same sequence occurring again the next time the pedal is depressed)
I have reviewed the following and done the following troubleshooting to try and figure this out:
1) Verified brake fluid between Min and Max on MC reservoir
2) Verified ABS cycling at 5mph upon initial startup; no ABS light lit and no codes saved
3) Verified no calipers are sticking; no abnormal wear or coloration seen at the rotors or pads
4) Verified vacuum at manifold (21 inHg @ idle), and verified no leaks between booster and manifold
5) verified booster is at least operating (check valve is ok, pedal is different vacuum vs non-vacuum)
- Disconnecting the ABS harness did not change the problem (dash lights lit and no speedo, so verified ABS not in the loop)
- Disconnecting the booster vacuum line does make the problem go away; obviously the pedal is very firm, but no kick is felt and no change in braking occurs with pedal travel.
- The dealer insisted on replacing front pads and rotors, to no avail (I should have known better...). I suspect the booster is bad at this point, but have never heard of one failing in this manner.