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Hello, USA 2008 Toyota Yaris with no ABS (confirmed with toyota & mechanics) . Brake pedal pulsates / shakes when pressing on brake from 1/4 way down to bottom (mostly) when car in motion and when car is completely stationary. No impact on steering or anything else, ONLY the pedal. Happens about 75% of the time. Brakes hold fine, do not feel spongy or anything else.

WHEN I press hard on brake from 40-60mph down to 0 (almost locking wheels) braking gets perfect (no pedal vibration) for at least a few mins afterward until brakes get cool again then pedal vibration resumes.

The shaking is pretty significant and you can even hear it from the
passenger side. Following done to no avail:

1) Changed rotors (no improvement)
2) Changed brake booster, and all valves, connections etc into brake booster (no improvement)
3) Changed Master brake cylinder, diaphraghm etc and im assuming fluid when this was done (reduced intensity of shaking for a short time but then got bad again)
2) Checked wheel lug nut torque
3) Checked brake caliper & caliper bracket mounting bolt torque. Torqued mounting bolts inspected for wear, looseness etc. including worn mounting brackets, bushings and sliding pins.
4) Checked wheel bearing for looseness.

Toyota/mechanics cannot figure it out. What could be the problem?  

Thanks..

Rene  

wait... the pedal pulsates when the car is sitting still????????

or when moving slowly...

i would pick up some 1/2" grade 8  flat washers at the hardware store...

take the front wheels off...      put 2 washers on each wheel stud... put the lug nuts back on...    with the lug nuts tight...  and the car firmly supported on jack stands... with the parking brake on... i would start the engine.. put it into drive.. release the brake pedal so the front brake rotors are free to spin....

look closely at the rotor for run out.. look at the calipers on the brackets.. are they moving back and forth..???

if so....  step on the brakes.. to stop the front rotors... return the transmission to park...

remove the lug nuts...  remove the caliper bolts.. remove the caliper bracket...    remove the rotor.....

examine the face of the HUB where the wheel studs stick through...  stick a straight edge across it at an angle..  its possible that the wheel studs were over tightened at some point and the studs stretched... not just stretching the studs.. but deforming the face of the hub..  when the area around the wheel stud is raised... the rotor cannot fit flat.. so changing the rotor again and again... won't help you ...

i would also... like you to examine the caliper slides... make sure they are free to slide...  i have found several earlier model toyotas and a lot of other cars that the caliper slide pins were totally frozen in place.. rusted ... or what i have found several times is the wrong grease was used....   what.. yep...

there is a grease for under ignition modules called silicone dielectric tune up grease..... it actually has dissolved sand in it.. when heated... it will become sand again..   locking sliding or threaded parts so tight.. they will never come apart ...  

i had one brake caliper slide that i could not budge with the 20 ton hydraulic press..   i have seen mechanics walking into the parts stores with drum brake adjusters.. that were locked tight also....

this is what the yaris wheel stud looks like



one thing.. i usually have to grind a angled flat on the head to get them in without damaging the threads... look at the old ones for how much to grind...

this is the wheel hub....  do you see how flat the surface is...




these bolts were identical..  one was over torqued...  same thing happens with wheel studs...



the threads will become farther apart.. and the diameter will get thinner..