[JuneBug]

I'm with you, Mainia! With the braking system you do not take chances. I would go OEM all the way. Here's hoping your wife never has that problem again.

 

[pdqtimetrialer]

So I replaced the master cylinder with a certified Toyota master cylinder and was feeling good about it. 2000 miles and no problems but...

I took the master cylinder to the dealer where I purchased the Rav4 and told the general manager our tale of woe. He agreed to order a replacement master cylinder and compare it to mine. If it did not have the marks, he would investigate further. If it did, then the assumption was because it was intended to be that way. Much to my surprise, he called me two days later and the replacement master cylinder bore he pulled from stock was gouged as well!

I lost confidence in Toyota and ordered an aftermarket master cylinder from Beck Arnley. This one has a nice smooth bore like I would expect. I finally got time today to install it, and pulled out the Toyota replacement part I installed two months ago. Sure enough, the Toyota part was also gouged - making three master cylinders all with the marks.

Toyota doesn't make the master cylinder - Akebono does, and they make them for Ford and GM and a bunch of other brands. They are normally considered a reputable brand. I searched the US patent database for filings from Akebono trying to find any data to either say why the marks are there, or find engineering information that specifically mentioned the bore should be smooth. No such luck.

The next step I plan to take is to section the replacement Toyota master cylinder with a band saw. Then I'll take pictures and post them here and at the NHTSA website.

Its scary to think others are having the same issues. Please don't ignore it.

In response to the potential cover-up repair. The master cylinders have serial numbers that are traced to the VIN number of your car. Should it become necessary, it would be possible to prove/disprove the master cylinder was repaired by checking to see if the serial number structure matches. You may want to ask the dealer what the serial number on should be without them looking at your car. They probably won't provide it. Toyota does a good job of circling the wagons to protect themselves.

Important! Anybody who has this issue should file a report on the NHTSA website. If they get enough reports, the NHTSA will open an investigation.

 

[pdqtimetrialer]

I'm still working on getting the second Toyota master cylinder sectioned. In the meantime, here are pictures of the master cylinder that Toyota Motorcars showed me and the nice smooth bore of the Beck-Arnley part now in the car. Motorcars' philosophy was since Toyota made it that way, it must be right. The mechanic said they marks are normal for a casting. He obviously did not have any machining experience.
Part of my job is designing die cast parts so I'm quite familiar with what the parts should look like and how they are made.

Since three different master cylinders from varying locations and dates all the marks, likely most if not all RAV4's have the problem.

I found a spot to email Toyota directly and sent them the pictures asking why the bore is scored. My guess is they will never respond.
https://www.toyota.com/support/#!/app/ask

 

[Butts]

Sent pictures and question to IIHS. Let them question Toyota.

 

[pdqtimetrialer]

This next set of pictures isn't for the faint-hearted. The bandsaw plan for sectioning the casting fell through. Instead I put a new blade in the trusty hacksaw and cut as straight as I could for a cross section. The observant folks may notice a small hole in the end of the casting. I drilled that to use a tool to push the inner piston out of the housing. All the marks in the bore are from machining, not my saw.

My guess is that all 2015-2017 Rav4 have master cylinders that look like this.

This was a new certified Toyota master cylinder, not an aftermarket part.

 

[pdqtimetrialer]

I am happy to report that Friday afternoon I got a call from Toyota about my email. I had a lengthy conversation with the Toyota representative, who put me hold several times, presumably to talk with a technical person as she had never encountered a situation like this one. Towards the end there was concern in her voice about the potential of a safety issue. A new case number has been opened up and it was recommended I visit a dealer.

This morning I spent quality time with Jim, the service manager at Classic Toyota (Mentor Ohio). Unlike Motorcars, who never contacted the regional rep when the brakes first failed, Classic put effort in to trying to find out what the problem was. Jim had never seen a master cylinder cross sectioned before, not really a surprise, but could see where there would be potential for the cup seal not to be fully supported. I left the parts with him and he will talk with the regional rep on Monday. I stressed that at this point I am curious if the marks are there intentionally, and if so, what is the purpose.

The latest picture shows the area of biggest concern. Without support on the back side of the cup seal, the seal could deflect and leak resulting in no braking force.

 

[Butts]

This next set of pictures isn't for the faint-hearted. The bandsaw plan for sectioning the casting fell through. Instead I put a new blade in the trusty hacksaw and cut as straight as I could for a cross section. The observant folks may notice a small hole in the end of the casting. I drilled that to use a tool to push the inner piston out of the housing. All the marks in the bore are from machining, not my saw.

My guess is that all 2015-2017 Rav4 have master cylinders that look like this.

This was a new certified Toyota master cylinder, not an aftermarket part.

Really appreciate your effort in pursuing this. Great idea of sectioning the master cylinder.

 

[pdqtimetrialer]

After more research, I'm thinking those grooves might be placed intentionally. I've been scanning through patents (can you tell I'm an engineer?) and there are many of them about the details of the seals within a master cylinder.

This one says the grooves are present because it makes it easier to get air out of the system. Maybe it makes for a faster install at the factory. https://www.google.com/patents/US7401468. Other patents talk about the seals function as "check valves" - sealing in one direction but not the other. This is claimed to help flush any particles that might accumulate on the seal area; another claimed it allows faster filling of the hydraulic chamber for ABS/VSC devices.

It best to take patents with a grain a salt. The patent office does not verify if the invention works or if the advantages claimed will materialize. It just verifies that nobody else has laid claim to a particular design. I read one abstract that stated it was fixing the number of "invalid pedal pushes" of previous designs - in other words, pressing the brake pedal and the car does not stop.

Here is a patent for a stick that is a dog toy.
https://www.google.com/patents/US63...s/US6360693?dq=6360693&hl=en&sa=X&ved=0ahUKEwigiK66o5vWAhXB34MKHcK1BP8Q6AEIKDAA

I should have investigated the spots in the grooves more thoroughly before I handed the parts to Toyota. I immediately rinsed the parts in water after cross sectioning, and later tried to wipe the spots out with a rag. They seemed to be adhered to the groove wall.

It will be interesting to hear Toyota's response. If nothing else, the quality of the machining is poor.

 

[pdqtimetrialer]

So I brought the cross sectioned master cylinder to Classic Toyota. Jim the service manager contacted the regional tech, who declined to look at the part since it had been modified. So I took it back and brought him the original, unmodified master cylinder that had the problems for test. After 4 weeks, I got a call 2 days ago saying that the regional tech doesn't want to look at this one either, since I had disassembled the pistons. Rather convenient for Toyota. If you do the work yourself, they won't look at the results; yet if you ask them to fix the brakes, they say they won't because the problem can't be repeated. At least we have driven 4000+ troublefree miles since I have done the repair.

Another NHTSA report of brake failures was reported for 2017 RAV4's.

Not much else I can do at this point.

 

[wjcrossen]

I have a 2018 Rav 4 LE with a soft pedal .. did the aftermarket master cylinder from Beck Arnley firm up your brake pedal? thanks for a reply .. wjcrossen@gmail.com

 

[pdqtimetrialer]

Most of the time the pedal was firm. The problem was sometimes there was NO pedal, and it went straight to the floor without resistance. 80,000 miles with the Beck Arnley master cylinder and there have been no problems.

A soft pedal could be a variety of things - leaks, air, or master cylinder issues. If you put the Rav in park and press on the pedal, does it hold firm or continue to depress to the floor? Thats a good way to test the master cylinder.

Most people don't bother, but its a good idea to flush the brake fluid every few years. If it is brown, it is time to do it.

 

[Jishay Smallhorn]

This YouTube video does a good job at explaining ABS. You can see that the hydraulic system is closed. The ABS motor simply blocks pressure from getting to individual wheels when the computer determines that the wheel is locked up.

If the valves in the ABS motor were to be stuck in the open position, then the car would operate like a car without ABS. Keep in mind that these valves should be fully open under normal driving conditions. This condition would not allow the pedal to sink to the floor.

If the valves were to be stuck in the closed position, then no pressure would reach the wheels and the vehicle would not be able to stop, but the pedal would be even firmer and harder than normal because the pressure from your foot would have nowhere to travel. Normally the pedal will drop an inch as fluid is pushed into the various brake cylinders on the wheels.

Vehicle Stability Control, simply uses the ABS hydraulic pump to apply the hydraulic pressure automatically (rather than you using your foot) and the same valves used by the ABS system determine which wheel(s) get the pressure.

So as mentioned in the earlier post, a problem with ABS or VSC would not cause the pedal to sink.

This is not true. I had a similar issue where my abs failed without code due to bad fluid. after replacing it, the pedal returned to normal