imported_f4guy905

Me and my friend were working on my car putting in a new alternator and rotors. What we did was replace the old rotors that were on my car with a better set from my friend. After the rotors were installed, I hopped into the car and pumped the brakes a couple of times to make sure they worked (remembered having to do it for my motorcycle). After that, I started driving down the street, thinking the brakes would be fine and BAM, they weren't. We took a couple of spins around the block slamming on the brakes every couple of seconds, but nothing improved. When we got back to the house, I spent another 5-10 min. pumping the brakes, but nothing improved. The brakes hold pressure when the car is off, but when it's running, there is none. The two front brakes had not air in them when we bled them, and the rears......well, my friend couldn't get the passenger side one off. Any ideas on what is the problem??

MAtt

imported_Cablerat

So the brake pedal sinks to the floor? or it's really soft? or it dies out really fast?

The brake booster has a vacuum line going thru a one-way check valve into the brake booster. Inside the booster is a diaphragm and a couple of valves.When the engine is running, it sucks the air out of the brake booster on both sides of the diaphragm.

Then when you press the pedal, a rod pushes the diaphragm in the booster as well as lets air enter into the back end of the booster. At the same time the valves inside the booster close and do not allow air into the front side of the diaphragm. So one side stays a vacuum(which is low pressure now), the other is filling up with air.. so that air pressure helps push the master cylinder in along with your foot pressure.

Hence "power brakes".. hope that made some sense.. lol

Then when you let go, the valves open up again and the engine once again sucks the air out from both sides of the diaphragm

The check value only allows air to release from the brake booster, not go in.. so id's say first check the valve and the vac line.. Make sure it's still functioning as a one-way. Then check the vac line.. Make sure it's not cracked and leaking air, otherwise the engine cannot create the vacuum.

Also, if the master cylinder seal is going, the pressure being applied may be leaking out.. You have to test all these piece out 1 by 1, easiest to check too the hardest to check,.

imported_f4guy905

good idea, thanks! But one question, where is the brake booster/check valve?

Matt

imported_cet_civic

the vac. line is going into the top left hand side of the booster....follow it back about 8inches and you will find the check valve

bbarbulo

iTrader: (2)

it's the thickest vacuum line you'll ever see on a car can't miss it

imported_f4guy905

lol, but where is the brake booster? I know, I am retarded, but I need guidence, lol.

imported_f4guy905

I just went to look.......is it on the right have side? The brake booster is the circle thing right behind the master cylinder, right? Then out of that, is a vacuum line that runs up and along the fire wall, there is a white little thingy about halfway to the intake manifold, is that the check valve?

Matt

imported_Cablerat

Yep that should be it..

imported_cet_civic

on the firewall in front of the driver


item 6 is the check valve

imported_Cablerat

Where do you guys find those pic layouts?!?

imported_cet_civic

www.slhondaparts.com

imported_f4guy905

Ok, I have the valve sitting in front of me.......I can blow though it, but when I suck, it won't let me. I am guessing the valve is still good then?

Matt

PS-what is the change of the brake booster diaphram being torn? I am guessing that is alot more work, but i thought i would cover all the bases.

imported_Cablerat

Ok so valve is good..

Not sure what the chances are of the diaphragm being damaged..

Make sure the vac line is connected and doesn't have any leaks.

Cna you clarify the problem?

Is the pedal really soft almost sinks to bottom? Does the pressure die out quick?

imported_f4guy905

it pretty much sinks right down to the floor when I try stepping on it. I try to pump it to buildup the pressure, but nothing happens. If the car is off, the pedal will stay solid with no signs of leaks.

Matt

imported_Cablerat

it stays solid when the car is off, but it the pedal is still low down..

Does the pedal come back up when you let go?

And you said you bled all the brakes except passenger rear?

The master cylinder has 2 pistons with 2 seperate lines for the brakes, 1 for fronts, 1 for rear. So if one of the brake lines gets a leak, 2 of your brakes will still function. When the cylinder gets squeezed, the first piston compresses the fluid and forces it into the brake line. That piston then pushes against the second piston providing pressure to the second brake line. If there's a leak in the brake lines, the cylinder will compress more... making the pedal sink lower down.

You sure you don't see any brake fluid leaking out anywhere?
Is your resevior full and the cap is on properly?

Could be lots of air in the one line you didn't bleed.. Unlikely, unless you actually replaced the shoes and drum cylinder in the back.

imported_f4guy905

The pedal would come back up to the resting position after pressing down on it. Also, there is no signs of fliud loss from anywhere around the car, and from the resevior. We are guessing that maybe we will bleed the whole brake system again and just try over. I really can't think of anything else that might be cause a problem.

MAtt

imported_Cablerat

There's a seal between the master cylinder and the brake booster. Have someone pump the brakes with the car on while you listen for and feel for air leaks around the cylinder and booster.

Aside from that.. I would look at the metering valve and proportioning valve.. I'm not sure if hondas have pressure differential switches.

Here's some info i found on them

Metering Valve

The metering valve section of the combination valve is required on cars that have disc brakes on the front wheels and drum brakes on the rear wheels. If you have read How Disc Brakes Works and How Drum Brakes Work, you know that the disc brake pad is normally in contact with the disc, while the drum brake shoes are normally pulled away from the drum. Because of this, the disc brakes are in a position to engage before the drum brakes when you push the brake pedal down.

The metering valve compensates for this, making the drum brakes engage just before the disc brakes. The metering valve does not allow any pressure to the disc brakes until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in.

Having the rear brakes engage before the front brakes provides a lot more stability during braking. Applying the rear brakes first helps keep the car in a straight line, much like the rudder helps a plane fly in straight line.

Pressure Differential Switch

The pressure differential valve is the device that alerts you if you have a leak in one of your brake circuits. The valve contains a specially shaped piston in the middle of a cylinder. Each side of the piston is exposed to the pressure in one of the two brake circuits. As long as the pressure in both circuits is the same, the piston will stay centered in its cylinder. But if one side develops a leak, the pressure will drop in that circuit, forcing the piston off-center. This closes a switch, which turns on a light in the instrument panel of the car. The wires for this switch are visible in the picture above.

Proportioning Valve

The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

imported_f4guy905

wow, thanks for that info. Sorry to ask this again, but where is the proportioning valve and the metering valve? And what do they look like?

imported_Cablerat

Not sure about where it is on hondas.. mind's running a blank right now

imported_f4guy905

that pic helps a bit........but how would I go about checking them? There is brake fluid running through all of them right? so if one was faulty, then it might be leaky? I really don't know how else to check it.