4 instances of brake failure in the last 3 months. Pedal goes to the floor with no braking. 2009 RAV4. Three different shops have looked at the car - each one reporting that all is good. Currently it's at a Toyota dealer. I have two theories - but I'll hold off until some people weigh in. Unless something definite is found, I'd like to retire the car. The driver has been lucky 4 times - however there was substantial damage in the latest incident. Between each incident, the car was driven for many days/weeks before the next incident occurred. The driver has been driving the car since new - so they should be familiar with the car.
Intermittant brake failure
- Thread starter tomcat27
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I'm going to guess air in the ABS unit, that manifests when abs braking is called for by the ecm.
That happened a few times with my '83 Accord. Then the master cylinder failed completely. Thankfully that happened at a stop light and not as I was driving in a not so smart way a week or two beforehand.
ABS definitely adds a layer of complexity and presumably other diagnostic steps.
ABS definitely adds a layer of complexity and presumably other diagnostic steps.
I'm guessing the M/C, or user error. I'm more inclined to think it's the MC. The Toyota dealer is "refusing" to replace it. ?!?!?!?!
They say this one is working and they've never replaced one. I say that the risk is too great. And what's the harm of replacing the MC? I would have replaced it myself already but I'm afraid of having to bleed the ABS.
They say this one is working and they've never replaced one. I say that the risk is too great. And what's the harm of replacing the MC? I would have replaced it myself already but I'm afraid of having to bleed the ABS.
That really sounds scary. Are you loosing brake fluid? If not I never just throw parts without diagnosing but in this case where multiple mechanics cannot Id what's wrong, I would. If you replaced the master cylinder and the Abs unit and thoroughly bleed everything I think that would likely cover your possible failure points . If there is anything else that could cause this hopefully someone else will chime in with their thoughts. Master cylinders (new not rebuilt) are pretty affordable. Abs units are usually very expensive and I'd try to find a low mileage junkyard or eBay one. Some ebay sellers list mileage and vins and you can verify mileage with a free online vin checker. Note - I'm not a professional mechanic but that's what I'd do if it were my car.
No loss of fluid. One shop said "all is well". 2nd shop replaced rear disc brakes and rotors. (this would not cause intermittant brake failure) The Toyota dealer wants to replace the front pads - they're at 50%. Once again, this wont cause failure. The last incident driver was pulling into a parking spot and hit the building. next time it could be fatal - which is why I want to retire the car unless something more substantial is found.
Replace the master. Bleed it using Techstream to get the air out of the ABS system.
Intermittent pedal to the floor when it works normally otherwise is either a bad master or a failed ABS module that’s bleeding the pressure.
Intermittent pedal to the floor when it works normally otherwise is either a bad master or a failed ABS module that’s bleeding the pressure.
The CareNut is local to Chicago area and is my first consideration. He open his own place, here is the info!
My Toyota, Lexus and Scion Specialist Repair Shop :TCCN Automotivewww.tccnautomotive.comMailing Address15751 Annico Dr Unit 3Homer Glen,IL 60491
My Toyota, Lexus and Scion Specialist Repair Shop :TCCN Automotivewww.tccnautomotive.comMailing Address15751 Annico Dr Unit 3Homer Glen,IL 60491
I can't see how a master cylinder can work normally most of the time then randomly allow the pedal to hit the floor.
Has the brake fluid been replaced regularly? Does the ABS activate when the pedal goes to the floor? Is the driver giving you the whole story as in, they were distracted when this happened and are are blaming the brakes? If it still has original fluid, I can image a piece of dirt in the system blocking a port preventing fluid from flowing or from building pressure. Then when the pedal is released, the dirt passes by and the brakes work fine for a while.
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I'd put a master on it, depending on the situation, I'd also consider bypassing the ABS module.
If it were my own personal car, I'd do both! If this is a customer car, I'd replace the ABS module, but that may cost more than the total car hence the bypass.
If it were my own personal car, I'd do both! If this is a customer car, I'd replace the ABS module, but that may cost more than the total car hence the bypass.
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More likely to be the ABS pump/module than the brake master.
Friend‘ odyssey did the same. It was maybe a 2014? At first it was once, then twice, and after a while seemed to happen once a week. couldnt be the master - when those go it’s consistent. The previous Gen ody had a tsb on sealing manufacturing plugs on the outside of the abs unit with glue and a metal cover... Occasional air getting trapped in the system during certain key factors, but the newer ones didn’t have the tsb so they wouldn’t try it. Dealer didn’t want to recommend the part to be replaced for $1500 and then that not being it. After a year of it they gave up and sold it. I still think it was abs … nothing else in the circuit could do that.
It's a relative's car. It's far away I don't know the service history. She has always taken it to the Toyota dealer for EVERYTHING - except the first few shop visits for this brake problem - because she was afraid to drive it very far.
Master cylinder. You can get Advics fairly cheap on RockAuto.
It depends on the edges of the rubber seal cups touching the walls of the cylinder. Once a little pressure has occured they are pushed out into good contact. If they don't touch from the outset, the pedal will go to the floor.
This is typically the end stage of a worn out M/C. There's usually but not always a warning in the form of the pedal dropping slowly when holding the car at a stop.
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What do all 4 wheel's brakes have in common? ABS and Master. It's one of those 2 things. If it were me I'd change both! That is a scary thing.
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