dahiya

Hi All,

Unfortunately, the battery of my RX350 drained (dont ask why) overnight and car would not crank next morning. Because of multiple attempts to start the car, I depressed the brake pedal 3-4 times using up all its vacuum (sorry, I dont quite know its actual technical name) and now brake pedal has become very stiff. I will install a new battery tomorrow but I wonder how will I start the car if I can no longer press on the brake pedal? I have not used all my might on that pedal so far fearing I might break something. Any ideas if I should REALLY push down on it, or, is there a non-brute way of doing this?

Barry2522

You will have no problem , put in your battery and just press brake pedal as you normally would at it will start .

salimshah

Get the new/charged-up battery installed first and with the right voltage applied things may become normal.

You can practically stand on the pedal without breaking it.

If things dont go normal after a good battery is installed, you can let out the fluid, by draining out of the bleeding nipple. [Please make sure what you are doing when dealing with brakes .. get help if necessary]

Salim

dahiya

Thank you both. Based on your comments, it sounds like a correctly charged battery is responsible for keeping the pedal normally operational/soft. All this while, I was under the impression that a running engine is responsible for keeping the pedal soft. Could you advise which one is correct - charged battery, or, a running engine?

If it is the latter, then I might continue to have my problem after new/charged battery is installed, correct?

(PS: I do not intend to challenge your expertise. Just curious to learn how it works.)

Clutchless

You used up all the vacuum in the brake power assist reservoir by pressing on the pedal with the motor off. Once the motor starts with the new battery it will provide you with brake vacuum assist within a few seconds. None of this will affect your ability to start the car or drive it safely afterwards. You will have no problems once the car starts. Everything you are experiencing is perfecty normal.

dahiya

And therein lies the problem. Please note that my car needs brake pedal to be pressed before motor can start. After new battery is installed tomorrow, I suspect the frozen brake pedal will fail to depress and therefore motor wont start. It sounds like the equivalent of cyclic dependency deadlock in computer science terms. i.e. Motor needs brake pedal to be pressed first; and brake pedal needs motor to run first..... lol

Thank you for the reassurance though. Glad to hear all this is normal.

vlad_a

What you're experiencing is absolutely normal. Brakes are completely functional. You can stop the vehicle at high speeds even when there's no vacuum left for power brakes - the hydraulic system is not affected by it.
If that was not the case, then vehicles would not be able to stop if the engine stalled. The only thing that is different is the amount of pressure required to operate the brakes. Yes, you will have to stomp on it. No, you won't break it. Yes, it will be back to normal as soon as the engine starts.

In other words, either get a good 'ol jump start, recharge the battery, or get a new battery, then stomp on the brake pedal and press the start button as you would otherwise. Engine will start and it will soon be back to norm.

dahiya

Awesome. This is what I was looking for and it makes sense. I will report back after I have had a chance to install the new battery.

salimshah

Any update?

Salim

dahiya

I installed the new battery and now the car is running well. As expected, the pedal did not become soft simply because new battery was installed. Thanks to the knowledge gained on this forum, I pressed significantly harder on the pedal and it did go down without breaking anything! Now I fired up the engine which provided for the vacuum mechanism and consequently pedal is now back to its normal self.

Lessons learnt: -
1. You cannot break a brake pedal by pressing really hard on it.
2. Pedal will remain hard to press after new battery is installed but before motor runs.
3. As soon as motor kicks in, the pedal will become soft again.

salimshah

Glad everything is ok.

Not to knit-pick your note, but for better understanding ... the brakes are not activated by vacuum in RX.

The ICE engine produces vacuum which is used for different things. Hybrid has alternative as the vacuum from running engine is not there.

The vacuum in your case is used to 'Assist' in applying force [in addition the foot developing the force] to apply the brakes. Analogy is power assist in steering ,... the driver has to apply less force or really less effort. Without the vacuum you were not getting the assist and you felt the brakes harder to push down.

Salim
ps: I explain this as there are vehicles which run the brakes on vacuum .. like commercial truck where the pneumatic system has to be built up before they release teh brakes [safety]. If you are near such vehicles, you can hear them leak out psst sound often enough.

ps to ps: As a driver one has to be prepared for emergencies and two orf those are 1) Engine racing up out of control .. you turn the ignition off [but never to lock position] 2) Engine stalling
When the engine dies you loose the vacuum and you need to be prepared to operate the vehicle without the power assist features. Stiff brakes and stiff steering. Driver is expected to steer and control in such situation.

dahiya

Thank you for this. Without knowing this, if I were in an engine-stalled situation, I would have totally given up on turning the stiff steering and/or pressing the stiff brakes because I would have simply assumed that both became non-operational. The fact of the matter is that both ARE fully operational - they just need more force to operate.

You sir, might have saved a life (or four) with that comment alone

JDR76

In case this comes up again in a search for someone else, you can start the engine without using the brake pedal.

Push the start button once to go into accessories mode. Then, without your foot on the brake pedal, hold the start button down for about 15 seconds and the car will start.

dahiya

Wow, thank you. I just tested this and it works very well.

vlad_a

Good call! I never even thought of the passenger engine start trick.