Brake problem, Need help!

[4runnersr5:D]

i have a 2000 4runner sr5. not exactly sure when this problem started, it might have been when my brother changed the brake pads.

so the problem is that when the car hasn't been driven recently (24hours) and its cold outside (less then 10c) the brakes are very weak after starting the car.

I drove from my parking spot, to a stop sign 15ft away right after starting the car last winter , and i slammed the brakes as hard as i could, i even pumped it like a mad man, and the car would barley slow down.

i was going 90km/h downhill (cold morning) and the light turned red, i had around the distance of 4-6 houses to stop, i slammed the brakes as hard as i could and pumping the brake to, but there was almost no breaking power.

the brakes have been bleed recently (though it would help, it didn't)

if i drive slowly and keep pumping the brake for 5 minutes after starting the car, the brakes are fine and powerful.by powerful i mean i could get the ABS to kick in by breaking a little rough. before its warmed up, no matter how hard i slam the brakes it will not have enough power to skid.

what could cause the brakes to crap out when its cold?

 

[FdcCal]

We need more info. How is the pedal feel when cold? Does it go to the floor, or is it firm, but the brakes are ineffective until warm? I had a Pathfinder that had metallic brake pads, and it was like that until the pads and rotors warmed up, really unsafe. If the problem started right after the new pads, look there. I suspect some fancy pads were installed. OEM pads work great..

 

[4runnersr5:D]

We need more info. How is the pedal feel when cold? Does it go to the floor, or is it firm, but the brakes are ineffective until warm? I had a Pathfinder that had metallic brake pads, and it was like that until the pads and rotors warmed up, really unsafe. If the problem started right after the new pads, look there. I suspect some fancy pads were installed. OEM pads work great..

it does not go all the way to the floor when i brake when its cold, it moves the same amount as if it were warm and you need to stop quickly (but not quick enough like your about to hit someone or something).

when it gets to that point(about 3/4 all the way to the floor) , it becomes rock hard and then i apply an ENORMOUS amount of force with my leg and it starts slowing down more.



maybe this will help explain things.

lets say when its warm you apply a force of 1x with your foot, the car would brake with a force of 10x (initial force was multiplied by 10) when its cold, you apply a force of 5x and end up with a braking force of 7x. its like you are literally slowing down the car with your feet.

but it doesn't just automatically get better at one point when its heated up, it slowly gains back breaking power while its heating up (being driven/braking)

 

[Stick Figure]

Very well could be the pad compound, the pads i run on my "fun cars" are like that .. first couple stops in the morning can be a bit sketchy.

only other thing i could see is the master cylinder could be going, but usually you will have fluid leaking somewhere, or have a noticeable different feel in the pedal.

 

[LittleCaesar]

it sounds like the brake booster check valve or possibly the booster itself. The former fails usually in the cold more often than not.

Check the line from the check valve to the intake manifold for cracks. Then pull it out of the brake booster (to the left of the MC) and shake it. An OEM replacement is about $30.

 

[4runnersr5:D]

so the rubber pipe from the booster check valve to the intake manifold (i assume) is fine and has a strong vaccum.

so either the valve is broken or the booster. i assume its just the valve, is that the 30$ OEM part you mentioned?

is it simple to remove and install the valve?

 

[LittleCaesar]

Yep, just pull old out and put new in. Less than 5 minutes. Similar to pulling a cork out of a used wine bottle.

Usually when the booster goes (I don't know of one failing on the 4runner, but anything is possible) the pedal will be stiff from the get go; you can't build up pressure via the MC, which doesn't sound like your situation.

You also may want to check the calipers (front) as well as the shoes on the rear to make sure both turn freely before laying down any $$$ for parts.

The part #, for my 99 at least, is 44730-60060.

 

[CaliCal]

bleed right?

 

[Reina]

Does the brake ever gets back to normal braking when it is fully warmed up??

 

[4runnersr5:D]

Does the brake ever gets back to normal braking when it is fully warmed up??

yes it does, and its not exactly when its "warmed up". its when its been driven for 5-15 minutes while pumping the brakes here n there to get it working.

i took the check valve out, my dad says it looks fine. but then again there isnt much to look. i called the dealership and its 80$ for the valve and 1200 for the booster, no parts stores seems to have the check valve only stealership.

can anyone tell if the valve is the issue from the pictures?

 

[LittleCaesar]

Not that I know of, but others may be able to chime in.

$80! Where do you live, Canada? What year is your vehicle?

Check both brakes, but especially the rears, before buying any parts.

 

[4runnersr5:D]

yes i do live in canada,land of the everything is ****ing overpriced by over 200% compared to the states.

and define "check the brakes", because the pads are new, brake fluid is fine, brakes have been bled (or bleeded? idk), ABS works, the hose from the booster to the intake manifold is fine, no cracks, pulled the check valve out and it seems fine, rear drum brakes have been adjusted recently.

i drove it a bit earlier, and i had to go around the block 2-3 times using gas and brakes, got to the point where i would just press the gas constantly and keep hitting brake with my other foot.

the brake pedal does NOT go all the way down, if i pump the brake pedal fast,but very lightly until it gets rock hard it seems that every time i take my foot off the brake and push again quickly, it goes down LESS then before. it got to the point to where i was able to move my the brake pedal like 3 inches max b4 it got rock hard.

I'm no expert, but it seems that it takes a little while for the vacuum to build up after braking, but WHY is it when its cold? what effect does the cold have.

also vehicle is a 2000 4runner sr5 3.4l automatic.

 

[LittleCaesar]

If you have done all that to the brakes, then I would say that it is the check valve or the brake booster itself.

The check valve allows a proportional amount of air drawn in from the intake manifold base upon the pressure one applies to the brake pedal to have the booster assist the MC in applying pressure to the pads. When the valve sticks, and it usually sticks in the closed position, no air is drawn in from the manifold to allow the booster to aid in braking, thus the hard as a rock brake pedal. Once the manifold air warms up, the check valve will open up. A mechanic told me this after I forked over $165 to have him replace my failed check valve on a Ford Bronco in 2000 while skiing in West Virginia. Try to drive down a mountain using only the Ebrake was an eye opener.

 

[FdcCal]

This didn't occur until the new pads were installed. I bet the new pads are the problem. Do you still have the old ones to slip back in for a test? I think it is some really hard pad material. You can also take the pads back and complain that they are DANGEROUS!