I wanted to see how firm the brake pedal would get when the car was off to judge whether the fluid needed changing. So I pumped the pedal until it got as hard as it got. Though past that point, I was still pressing pretty hard trying to feel for squish. I think I was pressing on it hard enough that I damaged something. Now, when I turn on the car, there's a large deadzone before the brakes start to bite. On the master cylinder side of the brake booster, it's of course used to this kind of pressure, but I don't think the pedal side of the brake booster is built to withstand someone cranking on it like this. Is there something I could have warped or stretched in the brake booster that would cause this long pedal travel?
Damaged the brake booster by pressing pedal hard with the car off?
- Thread starter oilylp
- Start date
What is your vehicle make/model/& year? I mean, I don't want to assume that the car is new(er), it may be an oldie!
Do you have ABS?
What is the brake setup?
F: Disc/R: Disc
F: Disc/R: Drum
You may have blown a piston sea in the master cylinder OR...if your car(I'm just thinking), has rear drum brakes, you may have blown out a cylinder in the rear. You really need to pull each wheel and inspect. If you have blown something, you'll see brake fluid.
UNLESS you have damaged one or more hydraulic lines(brake hoses) at each corner. These brake systems should handle a really hard stop such as in an emergency situation.
Do you have ABS?
What is the brake setup?
F: Disc/R: Disc
F: Disc/R: Drum
You may have blown a piston sea in the master cylinder OR...if your car(I'm just thinking), has rear drum brakes, you may have blown out a cylinder in the rear. You really need to pull each wheel and inspect. If you have blown something, you'll see brake fluid.
UNLESS you have damaged one or more hydraulic lines(brake hoses) at each corner. These brake systems should handle a really hard stop such as in an emergency situation.
master cylinder sees a lot more pressure when the engine is on and getting brake booster assist so i doubt you can damage the seals on it with engine off even if standing on the pedal. only thing you could possibly damage is the pushrod that links pedal to brake booster but even then iv never seen one bent or with damaged threads.
Thanks for your reply charbaby. It’s a 2011 BMW 3 series. ABS and disc brakes all around. No fluid leaks that I can see. The pedal isn’t sinking. I dont think that the force I was applying on the master cylinder (and by extension the brake lines) with no vacuum assist was any greater than what they experience during normal driving when vacuum assist is active.
In a brake booster is there anything that could be compressed or deformed that would cause play?
In a brake booster is there anything that could be compressed or deformed that would cause play?
Just saw your reply slybunda—thanks. On forums I’ve seen people ultimately trace low brake pedals to bad boosters. It’s counterintuitive given the fact that a working booster makes the pedal easier to press. Frustratingly, no one ever gives the explanation for a different kind of booster failure where the vacuum assist works but where there’s a low pedal.
My Jeep Grand Cherokee has push button start. You have to press on the brake pedal, and press the start button to start it. Sometimes if it sits for several days, when I get in to start it, the brake pedal is hard as a rock, and initially won't depress.
As soon as I press the start button, and the engine starts to crank, the brake pedal "gives in", and then depresses. The car always starts and operates normally. The brakes operate fine.
I just don't know what is causing the rock hard brake pedal.... "Sometimes". Most of the time it depresses slightly when I place pressure on it.... As it should.
As soon as I press the start button, and the engine starts to crank, the brake pedal "gives in", and then depresses. The car always starts and operates normally. The brakes operate fine.
I just don't know what is causing the rock hard brake pedal.... "Sometimes". Most of the time it depresses slightly when I place pressure on it.... As it should.
Things i have seen cause long brake pedal travel is:
Air in brake system
Leak somewhere which also lets air get in
Caliper seals causing excessive piston retraction
Air trapped in caliper slide pins due to excessive greasing of slide pins (this one was hard to track down but finally got it)
Air in brake system
Leak somewhere which also lets air get in
Caliper seals causing excessive piston retraction
Air trapped in caliper slide pins due to excessive greasing of slide pins (this one was hard to track down but finally got it)
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Having done the ABS/DSC hydro job on my 2007 E92 335, imho it's doubtful that pushing down on the brake pedal while the car was off would have damaged the system, but I believe in science and me having done the job 1X is not exactly statistically reliable nor valid.
If this happened to me, I'd basically do a brake fluid flush, with the hopes that all air would be forced out. If it still behaved the same way, now, unfortunately, I'd do the ABL bleed meaning hook up a laptop to the car and use software to do an automated bleed (BMW says this is required any time work is done such as replacing a caliper or in my case the entire ABS/DSC was removed for repair).
my .02 ymmv and good luck! The good news is that even DOT 4 is cheap, but the bad news is brake flushes are time consuming. The BMW is the only car in the stable where I do all 4 calipers, seriously, just don't want to spend the time on the GM and the Lexus. I cheat on those cars with the syringe, and that wastes a ton of fluid, but again, it's not that expensive.
If this happened to me, I'd basically do a brake fluid flush, with the hopes that all air would be forced out. If it still behaved the same way, now, unfortunately, I'd do the ABL bleed meaning hook up a laptop to the car and use software to do an automated bleed (BMW says this is required any time work is done such as replacing a caliper or in my case the entire ABS/DSC was removed for repair).
my .02 ymmv and good luck! The good news is that even DOT 4 is cheap, but the bad news is brake flushes are time consuming. The BMW is the only car in the stable where I do all 4 calipers, seriously, just don't want to spend the time on the GM and the Lexus. I cheat on those cars with the syringe, and that wastes a ton of fluid, but again, it's not that expensive.
I had some 80's GM products that had a dual cylinder master cylinder with a switch in the center. If one side was leaking somewhere the piston would push off center closing the switch and giving a warning light. It would also close off the leaking side. To reset it, you had to build enough pressure on the affected side to push the piston back to center. I learned about this when I was bleeding the brakes too aggressively and upset the balance in the system. Had to overbleed the opposite end to get it right again.
The vacuum is bleeding down, totally normal.
Please explain how that would tell you whether or not the brake fluid needed "changing".
Scott
Since brake fluid is hygroscopic, it becomes compromised over time as it absorbs moisture from the air, ultimately resulting in air pockets in the line. If the pedal is squishy after pumping, it indicates the lines need bleeding at a minimum, and perhaps changing, if one doesn't know the last time it was changed (as in my case).
I've never heard of the "test" the OP was trying to do... Pedal firmness to tell if fluid needs changed? I've been working on cars and trucks for a living for over 30 years and never heard of it. I go by fluid condition when I pull the cap or else I do so when doing other repairs to the brakes and I'm "in there anyway".
SammyChevelleTypeS3
$50 site donor 2023
Brake Fluid test strips: available at most local auto parts facilities.
Not how it works.
Brake fluid is hydroscopic meaning it absorbs moisture which is dissolved in the fluid. This lowers the boiling point of the fluid which means that under hard use the water can boil off leaving water vapour in the brake lines leading to brake fade. Once the brakes cool this water vapour will condense and be re-absorbed by the brake fluid. The water can also cause corrosion in the braking system.
You'd likely only be able to make the brakes fade through some seriously hard use. Pressing the brake pedal with the engine off isn't going to tell you anything.
