Search the Community
Showing results for tags 'brake booster'.
-
This was on an '03 2wd The brakes suddenly were not as effective. Had to stand on the brakes and even then, much reduced braking force. With the engine off the pedal would sink to the all the way to the floor. I thought the master cylinder went out since there was no hydraulic resistance felt at the pedal with the engine off. First: I inspected for leaks and found one rear wheel cylinder had a small leak. The exterior of the drum housing on the side facing the pumpkin had a barely discernable, small damp spot in the grime near the bleeder nipple. That wheel cylinder was bad, fluid weeping past the rubber seal, clearly visible when lifting the outside lip of the rubber seal. I swapped in a new wheel cylinder (fyi you don't need to take apart the brake shoes, just crank open the adjuster. After install is complete you have to crank it back closed while holding open the one way stopper arm) I power bled that line at the wheel cylinder -it was strange because it was difficult for the power bleeder to get a lot of fluid out of the line -but eventually enough came out that I considered it to be air bubble free. The pedal was still sinking to the floor... I slightly cracked each line (2 lines) at the master cylinder connection (while pedal was being depressed) to see if there was pressure passing out of the MC, there was. So I assumed the MC was good. I power bled more at all 4 corners TWICE pumped brakes with engine of and on, and still, not a lot of fluid was coming out, but enough that I thought maybe there are no air bubbles. Next I pumped pedal with the engine off, the pedal was firm, a good sign that the system was holding pressure and bubble free. Next I test drove and noticed an air hiss under braking, this is a telltale sign of a leaking brake booster. Next I swapped in a new brake booster and all is well. Theory: the rear wheel cylinder failed and allowed air into the line creating the sinking to the floor brake pedal. Then: maybe full extension of the brake booster under repeated 'pedal to the floor' strokes caused the brake booster diaphragm to tear? Takeaway: the master cylinder is fine despite the symptoms being indicative of a failed MC. Also: this is the 2nd replacement brake booster for this vehicle (master cylinder showed no leaks). 1st replacement BB was from O'Reilly's, a remanufactured unit from China bought in 2019, and was garbage, it start having a rubber squeak sound 2 weeks after install, and failed at 5 years. Upside, lifetime warranty on the original purchase, 2nd BB was no charge (reman unit for Mexico) -but not sure if the lifetime warranty applies to the replacement part. If you diy this have various extra ratchet extensions and wobblers on had, also deep well sockets. Working under the dash is a bitch so allow extra time.
- 3 replies
-
- brake booster
- wheel cylinder
- (and 4 more)
-
Hey team, I have a 99 Infiniti QX4, 4x4 w/ electronic transfer case. So for about two months I've had an intermittent "hissing" sound come from the under the dash, near the brake pedal during cold starts and occasionally while driving. The sound goes away as soon as the brake pedal is pressed lightly. The sound sometimes is heard while driving (but much less often than on the cold start), and will also go away when the brake pedal is pressed lightly. After reading a few forum threads, it sounds like there is a potential vacuum leak in the Brake Booster and/or valve nearby the brake booster, or that the booster is starting to fail. All the forums I came across did not have conclusive threads as to what fixed the issue so here I am asking you all what I should check first and if you all have any recommendations. Brake function has not changed since I began hearing this sound, the brake pedal seems to work the same as it did before with no loss of braking power or pedal play changes. Please let me know what you think! All information is appreciated and accepted. Thanks team!
- 1 reply
-
- brakes
- brake booster
- (and 9 more)