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Old 09-01-2010, 11:47 PM
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Brakes "Grabbing"

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.

Any thoughts?
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Old 09-02-2010, 07:14 AM
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This sounds like an odd one. I'd suggest calling the tech line for a Brake manufacturer (e.g. Raybestos, Bendix, Federal-Mogul) and seeing what they say. As an alternative I would considering asking that your dealer contact the Nissan Tech line for assistance.

Here are some phone numbers that you can contact:

Federal-Mogul, manufacturer of Wagner Brakes: 800-325-8886
Raybestos: 800-407-9263

I have called the Raybestos line before, and the tech rep is extremely knowledgeable.

Good luck.
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Old 09-03-2010, 07:52 PM
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Update

Thank you very much for the help Critic!

I contacted the Raybestos helpline and spoke with Bob (he was extremely knowledgeable and helpful). He had the following additional suggestions:

1) Inspect rear brakes and rotors for signs of pad issues or rotor scouring. The behavior is very common when rotor issues are present.
2) Verify vacuum rebound on brake pedal application and during the grabbing. Poor rebound (longer than 1 second) caused by a vacuum restriction/issue could be contributing.
3) Re-inspect front brakes to ensure proper application/installation.

He stated that the brake booster could be the problem, but that it would be the last thing to suspect after all else is ruled out.

I will let you know what I find from the above procedures.
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Old 10-06-2010, 01:54 AM
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Resolution

After several weeks of fighting with parts and lousy service procedures, I was able to finally solve the grabbing and "kicking" issue I was experiencing.

As it turned out, fixing this required the replacement of both the master cylinder and the brake booster. The following were things that were noted upon removal of the master cylinder and booster:

1) Master Cylinder was leaking brake fluid from the back-side seal, into the brake booster. There was fluid at both the o-ring seal and inside the booster.

2) The brake booster shafts (both the input shaft against the pedal and the output shaft against the MC pushrod) had significant play in them. The input shaft could be moved side-ways at least 1/8", and had a noticeable "click" or catch to it. The output shaft had at least 1/4" longitudinal play in it, as well as some side-ways movement.

I am assuming that the leaking MC caused the brake booster issues as described, although I have always thought that the brake pedal on this car felt "funny". I have driven the fixed car now for 3 days in various driving and braking conditions, with no issues noted.

Due to the HORRIBLE service procedures in the Nissan factory service manual, I will post an explanation of the steps I had to go through to remove the booster. The job is much more involved than the service manual indicates, but not particularly difficult for experienced folks with some patience.
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