Weird brake pedal feel

[walkenvol]

Pedal feels normal and car stops fine but after stopping and a short delay the pedal has to be depressed a little farther or the car will move forward. Is this a symptom of master cylinder failure? Its in a '96 Avalon with 4 wheel disk but that forum is not as active as this one.

Thanks in advance.

[fenixus]

it could be the master cylinder (weak seal in primary chamber).

but generally all those camry based cars have weird booster feel on the pedal right after stopping the car, I mean the vacuum changes after stopping the car and booster make the pedal feel a bit lighter right after pulling over and holding it down for 2-3 seconds.

either way car shouldn't move forward when holding the brake pedal down with same force (it can travel a tiny bit deeper because of booster vacuum).

other than that, when did you flush the brake fluid for the last time? you could have some water or air in brake fluid.

where is your engine idle speed at? high idle could cause car to move slowly forward in such scenario.

[walkenvol]

when did you flush the brake fluid for the last time? - UNKNOWN? Had the car for a few years and I've never flushed the brake fluid.

where is your engine idle speed at? - idle is the same as its always been. problem with brake pedal only recently started with no change in the idle.

Thanks for the response.

[fenixus]

I would flush the brake fluid with Low Moisture Activity Valvoline DOT3&4 or Castrol LMA fluid. both are excellent synthetic fluids.

regular DOT3 brake fluids collect 2% of water every year, if it was never flushed that means you may have up to 30% water in brake system (it's corrosive and friction may help destroy all rubber seals in MC).
http://www.aa1car.com/library/bfluid.htm

it takes around 32oz to do a complete flush through all calipers (from furthest to closest of Master Cylinder) and go from there. there is a DIY in CAMRY FAQ section here (check stickies for this forum).

If you find more than a few of black pieces (rubber) in old fluid during flushing then you *should* replace the MC next (it means that its piston seals are likely worn out).

other than that the rubber brake lines might be balooning under pressure.

[walkenvol]

I considered balloning rubber lines also. Thought I might get lucky and find someone else who has experienced the same symtoms to save me some time.

Thanks again!

[fenixus]

flush it first. edited post above.

[JohnGD]

Usually the symptom is pressing on the pedal doesn't yield much braking force until about 1/2 way down.

With the engine stopped pump the pedal to use up the vacuum reserve. Then gently press down on the pedal and see if it gradually sink towards the floor.

Then repeated, rapidly pump the pedal. And see if it firms up and rises each time.

Originally Posted by walkenvol

Pedal feels normal and car stops fine but after stopping and a short delay the pedal has to be depressed a little farther or the car will move forward. Is this a symptom of master cylinder failure? Its in a '96 Avalon with 4 wheel disk but that forum is not as active as this one.

Thanks in advance.

[walkenvol]

Usually the symptom is pressing on the pedal doesn't yield much braking force until about 1/2 way down. - Not the case here as the brakes work fine as they always have with normal pedal depression stopping the car. Once the car is stopped or just barely rolling where only a light amount of pressure would normally be required to keep the car stopped, the pedal will have to be depressed slightly farther or the car will begin moving. Pedal doesn't go to the floor nor does it have to be pumped to create stopping power. Everything appears exactly as normal except after I stop there is a delayed softness of the pedal requiring a slight farther depression.

Thanks for the response.

[ghettosled]

wonder if there is a slight leak causing loss in pressure. when changing the fluid, take note of the level in the reservoir and look for wet areas on the brake lines

[walkenvol]

wonder if there is a slight leak causing loss in pressure - haven't been losing fluid in the resevoir.

Thanks everyone for the suggestions as this symptom is one I've never encountered.