No brakes in the morning. It will definitely wake you up more than coffee.

[jamesd]

Ok.. the jury is in... They are saying it needs a new master cylinder. I will buy it at Autozone and have them install it.

[petrified.rabbit]

good luck with the fix..

Air in the lines CAN create an intermittent pressure problem, but its impossible to find without seeing the system.

[jamesd]

Thanks petrified.rabbit! I'm crossing fingers. Since my youngest daughter will be driving the car to high school I don't want to skimp on brakes. New booster and master cylinder will definitely give me a peace of mind knowing she will stop when she needs too. I picked up a new master cylinder for $122 at Autozone and includes the reservoir and bleeding kit.

[jamesd]

Hi everyone. Well the problem is back. My daughter couldn't brake when she was approaching the stop sign. The car did eventually but it took a lot of effort. This happened for a brief moment. After about a minute everything and braking resume like always. What is causing it? So far we tighten the brake line hose, bleed the system and still the same problem. New brake booster, same problem. New master cylinder, same problem. What's there to check or replace? I check all wheels and I dont see any fluid or anything in the inside of the wheel. Again the problem came back after a day short of a week after replacing the master cylinder. Also just before the car lost braking power the car sat in the drive way for 2 hours. Then my daughter got in the car to go to the corner store and that is when it lost brakes for a brief moment. Any suggestions? Thanks..

[xintersecty]

So lets say you fixed the mechanical side of things perfectly. Could there be a ABS failure that causing the brakes to loose power? For example the wheel sensor could be sending the wrong speed or the release valve is getting stuck. Does it even have ABS?

[jamesd]

No ABS, this is confirmed by the VIN# and no wires or sensors going to the wheels. This morning I took it to work and drove 13 miles in stop and go traffic. Everything works as it should, no hint of brake loss. I even slammed on the brakes a few times and it stops on a dime.. I did take a peek at the master cylinder for leaks or anything but on the brake booster I do see the black paint on it bubbling up around the area where the booster and master cylinder meet. Could that be from bench bleeding? I'm having it checked out again this morning. Very odd in deed. Somewhere I read about EGR valve could play role in this causing a vacuum leak. But no check engine light, no codes but... I do notice in the morning that the car seems to stumble a bit when starting up likes a losing power. But after the engine ran for a minute or two it levels out and works fine.

Side note: I'm not sure if this is important but I did have trouble finding a master cylinder for this car. Using the VIN# they came up with a part number for a master cylinder of GM 93742291 which is one with 10mm port valves. So did Autozone and O'Reilly. The one that was on the car was a 16mm port valve on there which I had to order from RockAuto since no one here carried it and GM had discontinued that part number. I ended up buying BECK/ARNLEY Part# 0729883.

[WyrTwister]

Do not know about now , but brake fluid used in the old days would mess up paint .

I do not think you ever fully answered the question about a check valve in the vacuum system ?

Do you have anything that looks like this ?

http://www.oreillyauto.com/site/c/de...rd=check+valve

God bless
Wyr

[jamesd]

Do not know about now , but brake fluid used in the old days would mess up paint .

I do not think you ever fully answered the question about a check valve in the vacuum system ?

God bless
Wyr

Hi WyrTwister! You are right, I did not answer the question regarding the check valve because to be quiet honest with you I do not know where it is or to look for. If someone could shed some light as into where it is because it does seem it maybe the issue. I assumed the check valve was inside the brake booster. I bought a new AC Delco booster and installed it myself. From there there is a vacuum hose that goes to the intake manifold. Nothing between the two other than the hose.

[jamesd]

Do not know about now , but brake fluid used in the old days would mess up paint .

I do not think you ever fully answered the question about a check valve in the vacuum system ?

Do you have anything that looks like this ?

Dorman HELP 80189 - Power Brake Check Valve And Grommet | O'Reilly Auto Parts

God bless
Wyr

I saw your link and I see nothing like that on my car. I've seen those on the brake booster right on the hose connection on other vehicles but mine did not have that at all. Where is it suppose to be connected too?

[WyrTwister]

I do not own an AVEO , our car is a Sonic . So I do not know how much they have changed . But I will take a look when I get home .

It may be in the brake booster it self ? Where does that hose connect to the engine to get the source for its vacuum ? Can you take a photo & post it ?

In the mean time , you might try the following test . Un-hook the hose at the source . Suck on the end of the hose , as hard as you can . Then try to put your thumb over the end of the hose , to hold the vacuum . Then release your thumb . Did it loose all the vacuum ? Or hold that inside the booster ?

I am wondering if what ever fitting that the end of the hose attaches to , at the engine , may have a check valve inside the fitting ?

I looked at photos of the booster , on line . The fitting at the booster appears to have no check valve at that point ?

This check valve appears to be a " universal part , and not specific for your car .

Dorman HELP 80189 - Power Brake Check Valve And Grommet | O'Reilly Auto Parts

God bless
Wyr