I just want to share with the community. This ‘Intermittent vibration on light braking’ drove me insane for 2 years.

Issue:
-intermittent vibration on light braking.
-vibration will shift from rear to front, depending on the degree I was pressing/releasing the pedal (WTF? Right)

Before the counter arguments begin…. such as warped rotors, sticky caliper, worn suspension parts, wheel bearings, rack and pinion components -> I’ve changed all of those parts and more…I think you’re gonna want to read this article, and keep this knowledge in your archive.

I changed freaken everything I can think of.
-went through 4 sets of rotors, and 4 sets pads (did bedding procedures every time)
-changed entire front suspension, and some rear suspension parts
-new brake hoses
-new shocks/ struts
-new wheels/tires
-new calipers
-did alignment hella times
-bled brakes hella times
-grease clapers hella times
-there were more stuff I changed… I just don’t remember it all right now

Regardless, the issue never went away (revisit the issue listed above if you’ve forgot it)

Then one day (2yrs later), I began to feel a slight difference in brake booster vacuum assist. Sometimes, I could brake easily with no effort…and during these times, there were no vibrations (light braking). In contrary, when the pedal felt just a bit lacking in vacuum, then the vibration would happen (light braking). Since I daily this car, I can tell when the brake pedal felt like it should’ve had more vacuum. It was not a cut-and-dry shut off. The lack of vacuum was so small that that you would have to really think about it when you press the pedal.

The light bulb went off -> If the booster would intermittently lack vacuum, then it would be engaging the first port more than the second port (ports on the master cylinder). Which means that some caliper pistons were half-engaging…. while other pistons were fully engaging. Then when I press hard, all the ports on the master cylinder would engage, and the car would brake smooth. This would explain the shift in rear to front vibration too.


Action:
I changed the brake booster, bled the brakes, etc,… and the vibration is gone. Braking is consistence, and much more powerful. BTW, changing the brake booster is a PITA. And I only had the single diaphragm one too haha.

Hypothesis:
I could be 100% wrong, but this is what I surmise. The intermittent lack in small vacuum, is what caused the intermittent vibration on light braking. The master cylinder would engage one port more than the other port (on light braking). Eventually, the rotors will get uneven pad wear. And since the vacuum was good some days, and was bad some days, I couldn’t really trace it down. The thing is: The lack of vacuum was so small that I never thought it was my booster. It was camouflaged for so long, Until the booster got worst, and then it all made sense.

 

well its good you found the issue and resolved it. just wondering if you did a vacuum brake booster test originally when you first initially had the problem instead of finding out the hard way and throwing a bunch of parts on the car. oh btw a vacuum brake booster test is a mechanical test performed physically on a booster, its not a test where you measure engine vacuum going to booster.

 

thank you for reading the post. i appreciate it.

ikr hahaha shoot..crazy. it's just that the booster leak was small, it camouflaged itself for years. Nothing lead me to consider testing it.

That's why I decided to write-up what I went through..I've have never read anything about a vibration issue that traces back to a bad booster. Pretty much I'm hypothesizing that the small leak in the booster is the first domino, and it trickles down and down and down..then the uneven wear on rotors is the last domino..I kept focusing on the tail, until I finally found the head.

I'm hoping this article will help someone later.

 

thanks for posting about your experience...you should post a DIY on changing the brake booster