Brake Problem

[ramminghard]

A friend of mine is having a problem with his brakes. There is almost no pressure when the pedal is pushed for the first time. If the pedal is pumped the brakes start to work. The car will barely stop. The master cylinder was just replaced 3 days ago by nissan. The pads are fine. I think that it is a bubble in the brake line and they need to be bled again but i am not sure. there is no leaking from the lines around the master cylinder. Any ideas. It is a 1990 nissan 300ZX.

Thanks
Matt

[DSM Power]

If he had it done at the dealer then just take it back and demand they fix it.

[Hollywood]

Originally posted by ramminghard
A friend of mine is having a problem with his brakes. There is almost no pressure when the pedal is pushed for the first time. If the pedal is pumped the brakes start to work. The car will barely stop. The master cylinder was just replaced 3 days ago by nissan. The pads are fine. I think that it is a bubble in the brake line and they need to be bled again but i am not sure. there is no leaking from the lines around the master cylinder. Any ideas. It is a 1990 nissan 300ZX.

Thanks
Matt

Easy...The brakes are not bled properly, no if ands or buts. It gennerally wont be one bubble, it will be a bunch.

[Hollywood]

It's brutal that they missed it. What stealership was it?

[THREE40SEVEN]

Air in the system will give you a spongy pedal.

I'm guessing the master cyl is faulty.

[RiceCake]

Probably just need to bleed the brakes, but if the work was done at the dealership I think they should be able to troubleshoot and fix it no prob.

[THREE40SEVEN]

Originally posted by RiceCake
Probably just need to bleed the brakes, but if the work was done at the dealership I think they should be able to troubleshoot and fix it no prob.

Originally posted by Hollywood


Easy...The brakes are not bled properly, no if ands or buts. It gennerally wont be one bubble, it will be a bunch.

How would pumping the brakes get rid of air in the system?

[Hollywood]

Originally posted by THREE40SEVEN

How would pumping the brakes get rid of air in the system?

I'm not sure what exactly you are asking, but I'll cover everything in hopes of catching you are asking.

When your brakes are not bled properly because of air in the line, you get the initail spongy pedal feel. For EX: You go to stop, you push on the brakes but find that the pedal is going close to the floor with limited stopping power, but if you quickly pump it again you will get more braking power and the pedal will not go to the floor as much but then will start to slowly desend to the floor.

Bleeding the brake rids the brake system of bubbles/air by pumping extra fluid out the system out of the bleeder screws on the caliper till all bubles come out and just fluid. And there are several methods of doing this. I have it down pact! I have a special technique.

[THREE40SEVEN]

You misunderstood my post- I know how to bleed brakes...

From what i understand from the original post, the brakes were working properly when it left the dealership. I HIGHLY doubt that it would have left the dealership with the pedal to the floor after having the master replaced.
How would the pedal feel/height change if theres no way for any additional air to enter/leave the system?
The reason that you get a spongy pedal is because air compresses. Liquids dont. Therefore, pumping the brakes would not correct for a low pedal as the air is still present within the system.
A leaky piston within the master cyl will cause the symptoms being described.

[Hollywood]

Originally posted by THREE40SEVEN
Therefore, pumping the brakes would not correct for a low pedal as the air is still present within the system.

But it does. I have fixed 2 cars with the problem discribed above by bleeding the brakes. And I have driven the 2 cars with the problem and both by pushing the brake pedal twice increased braking power when there was barely any braking power in the first push.

And one of the problem cars was actually started from a master cylinder that was replaced by a dealership! They never bled the brakes properly.

[THREE40SEVEN]

Originally posted by Hollywood


But it does. I have fixed 2 cars with the problem discribed above by bleeding the brakes. And I have driven the 2 cars with the problem and both by pushing the brake pedal twice increased braking power when there was barely any braking power in the first push.

And one of the problem cars was actually started from a master cylinder that was replaced by a dealership! They never bled the brakes properly.

I dont doubt that pedal feel will change by bleeding the brakes properly. We can agree on this...

Answer me this. How can the pedal height/feel get any better if the air didn't (and hasn't left) leave the system on the car in question?? Its still there, and its still being compressed.

[Hollywood]

Originally posted by THREE40SEVEN

I dont doubt that pedal feel will change by bleeding the brakes properly. We can agree on this...

Answer me this. How can the pedal height/feel get any better if the air didn't (and hasn't left) leave the system on the car in question?? Its still there, and its still being compressed.

My only guesstamation is that the air can only be compressed so much till a decent amount of fluid does enter the caliper enough to make it push the pistons at a reduced level of efficiency. By pumping the pedal twice quickly you are forcing that air to be compressed even more along with the fluid.

[THREE40SEVEN]

guess we'll wait and see what the dealership says...
Its so hard to say without test driving the car.

[ramminghard]

It was brasso nissan. The car is going back to them to fix it. It almost got us in a huge accident though. very frustruating because bleeding brakes is not a hard thing to do so a dealership should always be able to do it. Thanks for the help guys!!!!

[Weapon_R]

Originally posted by THREE40SEVEN
Answer me this. How can the pedal height/feel get any better if the air didn't (and hasn't left) leave the system on the car in question?? Its still there, and its still being compressed.

Even if you have air in the system, pumping the brakes a few times will force the fluid into the caliper anyways. If you've ever driven a car with air in the brakes, you'd know what I mean. The pedal does take a couple of pumps, but it eventually feels like normal, until you resume regular driving, and again it becomes spongy.

[THREE40SEVEN]

Originally posted by Weapon_R


Even if you have air in the system, pumping the brakes a few times will force the fluid into the caliper anyways. If you've ever driven a car with air in the brakes, you'd know what I mean. The pedal does take a couple of pumps, but it eventually feels like normal, until you resume regular driving, and again it becomes spongy.

I have driven cars with air in the system (inc my own car), and the symptoms are not the same as described by ramminghard. Pumping the brakes did nothing in my case... i just had a spongy pedal, which was corrected after a gravity bleed.

The reason i dont think its an air problem from not bleeding the system properly, is because (from what gather from the original post) the pedal feel has changed since it left the dealership.

You would have to have a leak in the system in order to change the pedal feel, saying that the master isn't faulty. Just because you can't see a leak doesent mean its not there.
hmmmmmmmm.......
Improperly adjusted drum brakes will also cause a low pedal, but i dont think that applies to ramminghards situation. Make sure that the master cyl is topped up as well.

[ramminghard]

The car has 4 wheel discs. The master clyinder was completly full. The car is going to get fixed at the dealership so it will be interesting to hear what they say.