mrod63

while I drive in the city the brakes are fine
But when I get on the highway after driving about 30 min I put my foot on the brake and it goes all the way to the floor of the car
As soon as I get off the highway it remains the same until a while passes and then they start working fine again
But I really think I need the breaks working good while on the highway it almost feels like I have no breaks the foot all the way down the car stops but it worries me
What could be the problem

zeronero

It could be that your master cylinder is going bad. Since on the freeway you don't use the brakes that often it allows more time for the fluid to leak out which makes the pedal go to the floor before the brakes work. In the city you use the brakes so often that you are continually pumping them which put more pressure in the master cylinder making them seen to work better.

I doubt it's the problem I just described but that could be it.

mrod63

Well I have checked the brake fluid level and that really never changes so as far as fluid leaking their is none
but your basic oil in this type of model that allways leak with high miles 300e 86 ?

zeronero

When my Master Cylinder had a leak it was internal and could not be seen from the outisde at all, or really even the inside, very small leak, no fluid loss. But it still made a big difference.

On the freeway for me it was hard to notice but at stoplights when I had the brake on for a minute or two the pedal would slowly fall to the floor and the car would start to move. I would have to pump it to gain pressure and to stop the car.

Kestas

The condition zeronero describes is a classic failure of the master cylinder. A quick check for this failure is to stomp on the brake pedal when the car isn't moving. If the pedal falls slowly to the floor, you need a new master cylinder.

If this isn't your case, you may be getting excessive knockback from the rotors. Do you get any pulsation during braking?

A healthy disc brake system always has the brake pads right up against the rotor, touching them ever so slightly. This gives the good brake response and 'feel' of the braking system.

Knockback is a condition where excessive wobble from the rotors knocks the pads back farther than they should be for good brake response. Highway driving maximizes knockback. On some cars I like to apply the brakes at least once on the exit ramp long before my stop so the brakes will reseat themselves closer to the rotor for optimal stopping. In you case it sounds dangerous. Check your rotors for runout while they are on ther car. The runout could be from debris or corrosion on the mounting surfaces. If you take them off the car for checking, the offending runout my disappear.

mrod63

Ok when the car is in the driveway I can pump those brakes all I want and their is no issue completely working infact I can pump them only about three times or so before they get to the point that I cant pump no more ( they get really hard ) so that seems fine to me
This only happens on the highway after driving for a while and like I said I can break no problem with that and the car does stop but its all the way on the floor at that point after a while of not being on the highway thats when they go back to normal

X-Man

Just curious - when you say "all the way to the floor," do you mean:

(1) there's still resistance in the brake pedal when applied, but it just travels farther down than normal, or
(2) the brake pedal actually travels as far as it can physically go (with minimal resistance) and you feel the stopper at the end (as when bleeding brakes)?

If it's the latter, it amazes me that you can stop as well as you say... that would suggest a delayed "booster" response AFTER you have applied all brake pressure. Dayam, you got *****.

mrod63

its number 1 but its really soft if I had to stop quickly it probably be number 2 but remember this only happens after driving a while in the highway it never happens in the city

zeronero

Well if it's really soft then that points to the booster being the problem. Since it's vacuum operated it could have easily developed a small leak.