I replaced two master brake cylinders on my 2006
Toyota Avalon. to no avail. I replaced them because the brake petal would go to the floor after 15 seconds. Both replacements acted the same. I have no engine light or code. The abs will work when I pump of to a full petal. At times pumping the petal several time will not get a full petal. I saw on UTUBE that a Ford had the same problem, and it was cured by replacing the ABS. Your assistant would be greatly appreciated. PAUL
Did you bench bleed the new master cylinders?
Did you get the entire system bled? Sounds like there is still air in there.
Anytime the brake system is opened before the ABS pump on your vehicle, it requires a factory level scan tool to command the ABS pump to position the solenoid valves to the “Air Bleed” position in order to bleed the brakes properly.
Tester
Do you know roughly what year that started and if it pertains to all makes? I’ve heard what you stated before, that a scan tool is needed for models with abs. But, I’ve replaced the master cylinder and bled the brakes on a 98 Dodge and a 94 GM with no problems and no scan tool. Maybe they were rear abs only and that is the reason…? Just curious.
Every Vehicle is different when replacing brake components.
That’s why you look up the procedure before providing a quote.
Tester
Ok. I didn’t know if a scan tool was required on all makes with 4 wheel abs or if there was some generic guideline like that. Was just curious.
I expect the problem is posted above,; i.e. the scan tool is needed to bleed the brakes properly after a MC install, due to the ABS. If all else fails it is sometimes possible to clamp off portions of the hydraulic system, to narrow down where the problem is occurring. For example if you clamped off all four rubber brake hoses at the calipers, and the problem remains, it has to be either the ABS or the MC.
I’ve had good luck diy’er replacing MC’s on my vehicles by first bench bleeding the MC, and making sure the tubes are full of fluid before connecting them to the MC. That usually does the job and no further bleeding is required. But my cars don’t have ABS. Ask at your local big-box auto parts store if they have a Toyota scan tool they rent-out, often as long as you bring it back in good condition, for free.
There was a master cylinder recall on this vehicle and several others, while there is an ABS brake bleed procedure it was not necessary. We replaced the master cylinder seal, bench bleed the master, installed and bleed the master again then bleed the system, no complaints.
The (old) Toyota Techstream costs $5800, how “often” have you rented one?
The brake system was thoroughly bled. I do not have a spongy petal, as one has when air in the system.
A faulty MC can definitively produce the symptom where you step on the brake pedal and it never firms up, just keeps going down, albeit slowly. When that happens the brake fluid is recirculating from the pressurized side to the non-pressurized side inside the MC due to a faulty internal seal. There are no external fluid leaks. Read what the poster “Nevada” says above, seems difficult to believe such a thing could pass the vendor’s part inspection process, but maybe both of the replacement MC’s being used were in fact faulty right out of the box.