Brake pedal vibrates-not rotor problem

[rradhay]

Hello, 2008 Toyota Yaris (no ABS) brake pedal pulsates / shakes only when pressing on the brake up to about half way down. No impact on the steering or anything else, only the pedal. Brakes hold fine, do not feel spongy or anything else. It happens more when engine is warm and happens when car in motion AND when completely stationery. It also does not happen with every brake press when engine is warm, but about half the time. The shaking is pretty significant and you can even hear it from the passenger side. Following has been done to no avail:

1) Changed rotors (no improvement)
2) Changed brake booster (no improvement)
3) Changed Master brake cylinder and im assuming fluid as well when this was done (reduced intensity of shaking slightly)
2) Checked wheel lug nut torque and tightened evenly to specification.
3) Checked brake caliper & caliper bracket mounting bolt torque and inspected for looseness. Torqued the mounting bolts and inspected for wear or any looseness, including worn mounting brackets, bushings and sliding pins.
4) Checked wheel bearing for looseness.

Champion Toyota said it happens with some toyota's :iono:when diaphragm shakes and it is perfectly safe and fine to ignore but i did not accept this and after complaints they changed master cylinder and brake booster to no avail and they do not know why problem still exists. They do not know what to do next. Also carried to independent mechanic who cannot identify cause after checking everything. What could be the problem?:frown::confused:

Thanks..

Rene

[yaris2010RS]

oddly enough on my way to school today my brakes did the same thing (only at one red light)
is it a come and go issue or is it always apparent? if it happens again i will def go to toytoa

as for ur issue, check front links and make sure they are tight/not warn out or any extra play. you may have to change break lines/calipers. are there any stanage ware marks on the disks/drums?

[marcus]

you sure its not the rotors being warped...otherwise im shooting for brake fluid bleeding is required.

[silver_echo]

start checking the vacuum lines, the one-way valve in there, and perhaps check to see if there is some issue with how well the engine is running(i.e. short term and long term fuel trim)

i was starting to lean towards the rotors as well, until i read your post a second time and saw the part about it doing it while sitting still...


also, i would like some more clarifying info...

trans? (auto or manual)
mileage?
engine light status/history?
mods?
how long has this been going on?
when did it start?
and the first time that you noticed this, was there anything done immediately before?
(if manual)does it do it with clutch pedal pressed or released or both?

[marcus]

vibrating while sitting? vaccum line..

[PhillyG]

vibration while not moving is definitely not in the brake system. something is causing your engine to vibrate more than normal and the result is being transmitted through to your foot. im acutally surprised your arent saying you are feeling it through the steering wheel, but that may be due to the brake pedal being "looser" and more prone to vibration. check a worn or broken motor mount, vaccuum leak, suspension looseness. those sorts of things let vibration travel much more than usual.

[yaris2010RS]

sorry op, didnt read that it happens when not in motion also. i would def check engine and for vacuum leaks. i dont think the issue is air in ur brake line but u might as well try it too. try to tighten the bolts on the master cylinder and booster, also check the seal between the booster (black round thing that the master cylinder sits on) and the master cylinder for leaks. either get someone to hold the brakes while u stick ur hand in and feel for "wind" or turn the car off and quickly stick ur head near the area and u will hear a hissing noise. does the pedal feel soft? can it be pushed all the way to the floor slowly?

[yaris2010RS]

also try to follow the brake pedal shaft, it connects the pedal to the booster and make sure its not hitting anything when partially depressed. i havent checked the route of one on a yaris yet, but on a 01 camry its a straight shaft that goes through the firewall.

the diaphram migh tbe messed up inside the booster. check ur brake fluid level and if it goes down check on the firewall between the booster and firewall, and if nothing check inside the car on the top of the carpet on the firewall where the brake shaft goes through the firewall and check for wetness.

[rradhay]

Thanks for the help of all you guys so far!!! Please keep it coming! I am collecting all the possibilities to pass to the Toyota dealers to check...When i do fix problem ill post back solution here..

trans? (auto or manual) - auto 1.5L 4 dr sedan
mileage? 50,000 miles
engine light status/history? - bought the car toyota certified used about 5 months ago and it had the problem when i bought it. Carfax report indicates no prior accidents or similar, not sure of this history
mods? - none, was previously used as a rental
how long has this been going on? - since i bought it 5 mths ago
when did it start? - would have been happening before i bought it not sure how long
and the first time that you noticed this, was there anything done immediately before? - not sure

Vibration happens when pressing on brake from rest point to about half way down (initial downstroke-0-60% down), As soon as brakes really start to grab to the bottom (60-100% down), there is no vibration.

[yaris2010RS]

calipers may be warped or something on the caliper end seized. many possibilities as jsut saying the brakes "vibrate" is a very generic way to put it.

i think the booster and check valve would be a good place to start as in ur previous post u said the master cylinder got replaced and it made it a bit better.