Is a loose Banjo Bolt enough to cause a total brake failure?
The car is a 2009 Mazda6 (manual transmission) with 10,400 miles on it. Here’s what happened…
I had just exited the freeway and was approaching a stoplight when I experienced total brake failure. I rammed into a light pole, but managed to avoid hitting any other cars. Thankfully no one was injured.
When I hit the brake pedal, it went all the way to the floor. It felt like I had accidentally hit the clutch instead of the brake. I panicked as I was heading for a red light at a busy intersection, so I did not think to use the emergency brake. I did try to pump the brake a couple of times, though. I am sure I did the wrong thing by taking the car out of gear but my reflex was to check the clutch to be sure I was not using the wrong pedal. I cannot say with absolute certainty that that there is no chance that I had been driving with the parking brake a little bit engaged, but I am pretty sure I was not. Even if I had, I was only about 10-miles from my starting point when this happened. It was raining but I had not driven through any puddles.
After I crashed the car, with the engine off, I put my foot on the brake and it felt normal, but when I started the car the brake pedal went all the way to the floor again and the engine roared until I turned the car off.
The mechanic at the collision center said it appeared that there was a loose Banjo bolt and that some brake fluid was leaking, but that the fluid level was still okay.
Three weeks prior to the accident, I had the car in for a routine oil change and tire rotation. The ?full circle inspection? earned a green light, so apparently there were no obvious warning signs.
Any thoughts on the diagnosis here? Are there some questions I should be asking the mechanic? Is there any way to find out what really happened?
Yes. A loose banjo bolt can cause brake failure.
A banjo bolt/fitting is what makes the connection between the brake hose and the brake caliper. If the bolt/fitting is loose or if either of the two brass washers/gaskets leaks it can result in the loss brake hydraulic pressure where the brake pedal goes to the floor.
Tester
However, that should only kill braking on two of the wheels.
You still should have had SOME braking ability and a red warning light on your dash…
These bolts generally don’t work loose unless disturbed by unskilled “mechanics”…There is more to this story…
The “red warning light” part is not true on most cars anymore. Way back when, the brake warning light was triggered by a switch that sensed a big pressure difference between the front brake lines and the back brake lines. Hardly (if any) any cars do it this way anymore. Most now trigger the brake warning light only when the brake fluid level gets too low. The OP says that the fluid level had not yet gone that low.
I do agree that I have never heard of a banjo bolt coming loose on its own. I wonder if the OP’s mechanic verified that the proper washer was installed.
“the brake pedal went all the way to the floor again and the engine roared until I turned the car off.”
I agree with the other posts, but the engine roaring bothers me. It may be an indication that the power brake booster has a vacuum leak.
Seems like you have a failing master cylinder. It’s not the usual way it fails but it has gone “part-time”. That loose banjo bolt was a minor problem that had nothing to do with lack of brakes. Usually when a brake booster fails, the pedal is harder to push.
Maybe the engine was roaring due to the crash damage?
I had no braking ability at all and no warning lights on the dash. All service on the vehicle has been performed at the Mazda dealership’s service center, but I do feel a bit like there is more to the story that I am not being told…but I don’t know the right questions to ask in order to get the whole story.
Is it possible that something happened when the tires were rotated?
It also seems odd to me that the brake pedal gave no resistance when the car was running but felt normal when it was off.
What’s even stranger to me is that the Service Manager at the dealership did not even want to do any investigating. He told me to have the body work done and then if the brakes still didn’t work I could have it towed over to the dealership. It seems to me that since his mechanic was working on the car just three weeks prior to this crash he might want to take a look at the car and see it for himself.
With regard to the engine roar…could damage to the control arm cause that? The body shop said the control arm was broken.
"It also seems odd to me that the brake pedal gave no resistance when the car was running but felt normal when it was off. " Actually, that’s one part of the story that’s not so odd. You have power assist on the brakes when the engine is running, and no assist when it isn’t. That’s normal enough.
I would want to find out for sure if there is or isn’t any braking occurring with the other two wheels before any brake repair is done. As the other poster pointed out, it sounds like a rare, complete, master cylinder failure.
I think that the dealership is afraid that liability for this will fall to them or to Mazda. They probably want as many people to touch it now as possible before it gets back to them. This way they can say that the other guys did it.
Unless the banjo bolt were so loose as to bleed off pressure as fast as the pedal is pushed it seems unlilkely that it would cause instant total failure.
All VERY GOOD points in your post. This one is screwing with my brain. I can’t figure out how the master cyl. could “come back” after a complete catastrophic failure though.
LOL on the Mazda dealer " the other guys did it"
This Collision Center that you refer to that has your car.
Is this a State owned accident investigation facility? Is your car there because they are trying to find fault with the car or you?
Whatever the case that place needsa new mechanic and the people who posted here that it needs a MASTER CYLINDER should apply for the job because they would be a lot better at it than the mutt that has the job now.
There is no way that you would lose 100% of your brake pedal due to the leaking banjo bolt.
You have a duplex brakeing system on your vehicle and you should have still had “some” brake pedal left and “some” brakeing ability albeit not great brakes, but some brakes.
This has to be a catastrophic failure of the master cylinder.
The only other possibility would be a coincidental failure of both halves of the system at the EXACT SAME TIME and what are the odds of that? None!!
If your foot hit the brake pedal and not the clutch by mistake, then ask this mechanic at the COLLISION CENTER how a banjo bolt leaking on only 1/2 of a duplex system could cause both halves to fail at the same time.
Doesn’t matter what his answer is, cuz it’s going to be wrong. It needs a master cylinder because it’s the only thing that controlls both halves of the brake system 
Thank you all for your very thoughtful feedback. I am going to hire an independent mechanic to diagnose the cause of the brake failure and have him/her put the cause in writing. According to the lemon law in my state, one catastrophic brake or steering failure is all it takes, so I will be asking Mazda to refund the full purchase price of the vehicle. It was only 11-months old and had 10,400 miles on it. I don’t care who you are…a car that new should never have that kind of flaw.