No brakes on first application after cold start.

[Sagaris]

Okay so the thread title isnt quite exactly how my problem is:

Three times within the past 500 miles (new brakes 500 miles ago)
I have had the brakes feel like there is no brake booster assist. Every time it has happened it was just a couple of pedal applications after first starting the car up. I press the pedal, the pedal does not depress like it should as if there is a brick under the pedal or the booster isnt working.

The chronological events of the 3 instances are outlined below to show you how they relate:

1st instance
1) Cold start, brakes held the car in place just fine while selecting reverse

2) Reversed out of my parking spot, brakes stopped the car normally to allow me to start exiting the parking structure.

3) As I approached the garage door to exit the parking structure, the brakes worked normally to allow me to check both directions and proceed out onto the street.
-everything up to this point has been <1500 rpm <5mph, total distance travelled is approx. 100 ft.

4) As I pull out onto the street. I accelerate up to 20-25mph travelling a total distance of 100 ft. and have to stop for a stop sign.

5) PANIC!!!! BRAKES ARE NOT WORKING PROPERLY! I step on the brakes, It feels like I described in the text above, like a brick is under the pedal or that there is no brake booster, after 1-2 seconds of steady pedal application, the brake pedal returns to normal , kind of like it breaks free and is totally normal.

6) Every single brake application afterwards is normal with no problems.

2nd instance
Exactly the same as the first, it happened at the same physical location under the same circumstances just leaving the same parking structure,a week or so after the first instance.

3rd instance
Exactly the same as the first and second instance, happened a week or so after the 2nd instance, except I was able to stop normally at the stop sign that it had failed at before, but the next brake application after that (50 feet later) was the one that caused it to fail.

I would guess that I have cold-started the car ~40 times in the past 500 miles since servicing the brakes and the brakes have felt excellent and perfectly normal all but those 3 times.

Brake work done:
-New pads, rotors, soft lines
-rebuilt rear calipers myself
-bought rebuilt front calipers
-new brake fluid
-brake system bled 3x, pads bedded , everything feels great


WHAT THE PROBLEM ISNT:

-This is not a case of low friction due to the pads being cold
-This is not due to air in the brake lines

I am thinking it has to to with the brake booster and the check valves. I am not very well versed in the operation of the brake booster (beyond the very basic idea that it operates off of engine vacuum) but when it comes to the check valves and how they are arranged, I do not know much about that.

I know this is lengthy, but has anyone had similar experiences?

I had a 2002 Toyota Rav4 that had this problem as well, it seemed to only happen in the cold and it was only during one of the first stops , it happened ~10 times in 20,000 miles on that car. I never resolved it on that one either but was looking into a check valve problem .

[unloadedak]

try getting some vacuum line and bypassing the check valve? i'm not running a valve on my swap, no problems whatsoever.

[Blackangusinc]

I wonder if the check valve is sticking.

[Sagaris]

I just went for a drive and purposely hit the brakes hard as soon as I got going ~15-25 mph. When I did, the problem was present and I pushed the brakes harder. It "pushed through" as usual but I noticed that the way the pedal sounded was just like when the ABS pump runs, although I could not hear the ABS pump running. I could feel a very toned down version of the ABS type pulsation as it "pushed through" but the wheels were far from being locked up since this was dry , clean pavement with new tires.

I did fail to mention that the ABS light came on after doing all the brake work 500 miles ago. I replaced a wheel bearing and supposed that maybe one of the sensors got dirty in the process (even though i cleaned them all) I checked the resistance on the front sensors and they showed proper resistance. I still have yet to check the rear sensors but they were not disturbed or unplugged at all unlike the fronts. So ever since doing the brakes I have had the ANTI-LOCK light illuminate and stay on whenever I go over 5-10mph (whatever the speed is that the system activates) and the ABS has not functioned since. HOWEVER on this 4th occurence of the brake problem, I noticed that when the pedal went hard, the ANTI-LOCK light was not illuminated and I surely had reached 15-20 mph. It continued to stay off as the hard pedal resolved itself and I reached 30-35 mph. So I gave the brakes a good push to try and lock them up and the ANTI-LOCK came on and stayed on as usual.

So while it seems like the check valve for the booster is sticking open just a tad, now it is seeming like an ABS unit problem

[Sagaris]

I do not know the black magic involved in the ABS pump. Is it possible for the ABS pump to partially block brake fluid flow when it is not operating? kind of like a valve that isnt fully open that gets forced open when I apply the brakes?

[xwill112x]

i would say the booster or somthing related around it. id have to drive the car to diagnose it myself :/

[Sagaris]

The only indication of a booster problem (besides a hard pedal) is the fact that I had a slow brake fluid loss. Fluid was/is leaking out either into the booster or out of the rubber grommets at the bottom of the reservoir (it appears to be the latter) . I don't believe it to be a booster problem for the fact that it is not a consistent issue. It seems like if the booster was on its way out that it would have a hard pedal consistently (every pedal application) or randomly ( not just the 1st pedal application).

I was thinking that it is check-valve related (which I still do)

But now that the ABS seems to be related, I am also questioning the ABS pump. I am certainly going to replace the check valves however I won't be suprised if that does not fix it.

I have a spare booster sitting in my garage but I need to get a good new MC for it.

[xwill112x]

Then i would look at the check valve.

[xwill112x]

So it does it once a week...hmm. install known good check valve or known good MC. My brakes were like this and i thought it was a check valve...had no air in lines at first, but as time went on air started shwoing in the lines and it turned out to be a MC.

[jlevie]

My first suspect would be the check valve or lines between the booster and intake. My second suspect would be the booster. The ABS unit is a possibility but I'd only replace that after I knew that the booster wasn't a possibility.