Brake pedal pressure variations

[CTS03]

Hi All

Has anybody noticed any variation in the pressure you need to apply on the brake pedal to stop? I have seen variations in my Corolla T Sport (31K km) from almost free pedal travel to the floor (not only after a brake liquid replacement) to very resistive pedal at its top position. It seems like variations in brake assistance.

Changes may be noticed after weeks or minutes!

In general, driving previously at high rpm usually seems to pump the brakes.

If a/c is on at a stand (foot light on pedal), whenever the compressor is activated the pedal moves down 1-2cm.

[Otaku]

Could be air in your brake system if they were not bled after changing fluid.

Also keep in mind variation between cold and hot brake effectiveness.

Sounds like you have a problem though, I'd have it looked at.

[Blackzze]

CTS03,

If your pedal EVER goes to the floor, you have a problem that needs to be sorted pronto.

I find with me the brake pedal can go down slightly if the A/C cuts in, I don't think this is a problem with the stivo, just a 'feature', i have noticed heaps of cars do it.

i find my brakes generally responsive in the pedal (5cm os so in general driving) and i really think i have never taken it over half way, and trust me, Ive skimmed my discs 2 times in 40,000ks from flogging it, and the pedal has never got over half way, i have had my abs kick in a couple of times in genuine emergency stops, and even then the pedal didn't go over half way.

I can't imagine trying to pull up in a hurry one day and have the pedal go the floor :o

Though from what you already describe with your flushing already, it could really be an electronic fault, you should still be under warranty yes??

Perhaps try disconnecting the battery for 15 mins to reset the ABS/EBD module, could be a random glitch there.

If no go:

I'd dump it back on the dealer and refuse to drivre it (unsafe to operate) until they fix it (demand a loaner for free). Or at least insist they change the ABS/EBD box and the filler container, and you be the test driver.

Just my 20c worth ;)

[CTS03]

Thanks both for your comments.

Indeed the response to a/c should be standard; I have also noticed this in a BMW car.

Today, I did some tests and determined a braking behaviour although I cannot be sure that this would be exactly true and reproducible:

The brakes appear to be pumped at high rpm of the engine when moving with 2nd gear, particularly noticeable above 4000rpm. After passing above the lift, changing to 3rd etc. (driving below lift) the pedal has much softer travel for long way to the floor. If this is not supposed to be so (e.g. to avoid easy wheel blocking at high speeds), it may indicate loss of assistance due to the lift activation?

I have been feeling these pedal pressure inconsistencies long time ago. I was sensitized to the problem again when my brake liquid was changed and I had to push the pedal to the floor. After 10 busy days I intended to go back but it changed to my "normal"! It could be trapped air that went through but inconsistencies were always here.

In any case, I am also wandering if it is usual in Corollas to feel significant pedal pressure differences after a brake liguid change or my mechanics did bad work?

Edited October 14, 2005 by CTS03

[Otaku]

If they didn't bleed the air from the brake system after changing the brake fluid then what you're describing may occur.

What happens is that the air in the system compresses rather than the fluid (which technically should be incompressable) reducing effectiveness and extending your pedal stroke.

Get them to bleed the brakes.

Blackzze is right, your brakes should never push to the floor or have that little effectiveness, unless you're driving a Commodore... :P

[Blackzze]

CTS03,

I haven't tried my brakes at such different engine speeds as you, I will try tommrow and let you know.

It is really worth remembering that brake accuation from your pedal is probably via vacuum assistance to the booster, so as your engine speeds increase, so will the vacuum, and therefore the pedal pressure, this is more apparent in older cars especially, but would normally make (guess here) 10-15% pedal pressure difference from what I have felt myself in driving older cars.

I tried my pedal today when i was stationary with the car running, and I can get my pedal down to about 65-70% travel, but as I said yesterday, my abs would kick in before the pedal got to 50% when I am moving.

And Otaku is right, unless you drive a commodore (or vauxhall omega to you!) :P

[CTS03]

After further observation, I definitely have non-negligible variations in brake pedal resistance. Yesterday night the pedal was extremely hard from its top position for a distance of ~10km. It could not move down beyond few mm-1cm! I could only correlate this with the high idle (1400-1500rpm) after a cold engine start at 15C.

My brakes operate eventually but I may loose important seconds due to my memorized force on the pedal.

I will have the car checked by Toyota in the next days, but I practically do not expect much: any pedal response may be considered "normal".

I guess a reset of electronics should be the starting point.

[Otaku]

Don't underestimate them, I'm sure they'd take a brake problem seriously because it has a high potential to be dangerous.

Seems perhaps your booster or master cylinder is playing up?

[CTS03]

The brakes' efficiency was measured: 66% front and 61% rear, both above the 50% threshold. Conclusion: OK.

Who cares about pedal's free travel variation? It is considered normal.

[sporthatch141]

I reported the same behavior RE: Impact of AC Compressor and break pedal travel. They stated - This is normal behavior and expected. Apparently it has something to do with the Booster?????

[CTS03]

Apparently brake pedal variations, noticeable to some of us, cannot be avoided. Just be alert that after the engine lift the brake pedal may soften dangerously. This becomes important e.g. to stop in-time infront of a red traffic light.