2G Brake booster & weak braking

[assault187]

Today I had to make a sudden stop from 150 ft from the car in front of me and I could not stop! If I hadnt swerved into the center turning lane I would have hit the car in front of me. I was driving at 50 mph and they brakes were cool at the time considering I only stopped twice from 40-45 mph within 3-4 miles. Tonight I checked the brakes to make sure nothing was leaking onto them or any leaks in the brake lines themselves, all checks out well. I also bled the system one corner at a time. Any ideas what would have caused this? Brake booster fault, possibly the master cylinder?

The car did not pull in any direction, pedal pressure felt slightly mushy, and the braking felt evenly applied but the braking was incredibly weak. The pads have good meat on them and the rotors are pretty fresh.

I Know the 1G's have one way valves from the big vacuum line from the rear or the intake manifold to the brake booster, Do 2G's have them as well? When I bought the car it was not present and didnt notice any adverse effects to the braking so I didnt think anything of it. Im assuming the valve keeps the boost pressure from entering the brake booster to prevent any damage. Anyone have any advice for checking the entire braking system or just advice on the situation?

After bleeding the brakes I took the car out this morning on the way to work and the brakes still seem weak. One of the ABS sensors is bad so I have'nt had ABS in a while now but I never had a problem, I could still lay on the brakes and lock the brakes up.....

I also noticed today that if I press the brakes while stopped and pump them, my Idle will rise about 1500 rpm. This is with no FIAV, or IAC on the car both were removed and blocked off.

[97eclipseNT]

if it was the brake booster you woul have a high/hard pedal due to having no vac assist. usually there will be a one way check valve in the vac line going from the booster to the intake manifold although i'm not sure what the 2g's have. check where the master bolts to the booster and see if its leaking. sounds like a master cylinder to me.

[assault187]

Thanks for the response! I'll check the master tomorrow and see what I can find. Is that pretty much the only problem that would effect the master cylinder is a slight leak? Now I know a leak will destroy braking but are is there anything else to it them a cylinder and flluid being dispersed?

[Defiant]

Originally Posted by assault187

I Know the 1G's have one way valves from the big vacuum line from the rear or the intake manifold to the brake booster, Do 2G's have them as well?

All boosted brakes do.

When I bought the car it was not present

It lives inside the vacuum line itself. Pull yours off and see which direction you can blow through it. You want the "blocked" direction going to the engine.

and didnt notice any adverse effects to the braking so I didnt think anything of it. Im assuming the valve keeps the boost pressure from entering the brake booster to prevent any damage.

It keeps the booster from losing its vacuum, and keeps boost from pressurizing the vacuum can.

After bleeding the brakes

In what order? The proper is RR, LF, LR, LF. Not the "usual" order.

I also noticed today that if I press the brakes while stopped and pump them, my Idle will rise about 1500 rpm.

Sounds like your vacuum line is on backward.

[asian312]

Good point on the bleed order. The service manual also says to have the car running while performing the bleed.

What type of pads are you running? Properly bedded in? Rotors have hot spots or deposits?

Also check your wheel bearings. I know this sounds crazy, but a slight play in the bearing will create a pad 'knock back' effect and feels exactly how you described. Basically the force generated by the brake system is used to straighten the rotor and not stop the car.

[assault187]

Originally Posted by asian312

Good point on the bleed order. The service manual also says to have the car running while performing the bleed.

What type of pads are you running? Properly bedded in? Rotors have hot spots or deposits?

Also check your wheel bearings. I know this sounds crazy, but a slight play in the bearing will create a pad 'knock back' effect and feels exactly how you described. Basically the force generated by the brake system is used to straighten the rotor and not stop the car.

I run KVR carbon pads and pro-slot rotors. The wheel bearing assemblys were just replaced maybe 2000 miles ago. This was the 1st time I have ever had this problem, the car usaully stops very well.

When bleeding the system my order was LF,LR,RR,FR..I was unaware of this order. Whats the purpose behind the bleeding order?

Im gonna run over the brake system again today including checking the valve at the booster and all.

[Defiant]

Originally Posted by assault187

When bleeding the system my order was LF,LR,RR,FR..I was unaware of this order. Whats the purpose behind the bleeding order?

It has to do with how the ABS is plumbed.