Recently I replaced my brake pads on my 99 legacy wagon (ABS 4 wheel disk). Afterwards I found that the brake pedal hit the floor as if air was in the lines. I thought that this was strange since I never had the line open, but I bled the entire system any way. The pedal felt a little better, but during a test drive I found that the pedal would hit the floor under hard braking and the car was only capable of coming to a slow stop. The brakes feel like they actually dump the pressure! I have experienced air in the lines before in other cars and this feels different. But its hard to tell because the brakes are so dam mushy on this car anyway. At first I assumed that I had just not bled the system enough, but 6 attempts and two large bottles of brake fluid latter I think that there must be something ells to this problem. And get this after using the car with unsafe brakes for a day or so the problem gets worse! There are no leaks that I have found and the reservoir dose not seem to get any lower.

 

 

 

Please some one help!

If there is excessive pad travel due to warped rotors for example, the brakes might feel like you are describing.

 

 

A soft rubber line might also swell under pressure and give you that feeling.

 

 

Can you pump up the brakes hard with the engine off?

 

 

Leaking master cylinder seals may also be to blame. I’ve read about putting a block of wood under the pedal to limit travel when bleeding brakes the two person way so the seals don’t contact a region in the cylinder that isn’t normally used and may be rough and corroded which will chew up the seals.

 

 

Good Luck.

 

That’s an interesting theory worth looking into. I am thinking about rebuilding the master cylinder as an act of desperation. Anyone else have any ideas? I am interested in hearing any suggestions. Has anyone ever heard of problems with the proportioning valve or ABS system? The first thing that went through my mind after replacing the pads is that I might have damaged one of these items when I used a c clamp to push the pistons back into place. Though I have been doing it this way on my other cars for years.

One more question for you guys. Why did I have pressure problems to begin with when I never opened the lines? Is major pressure loss normal after putting in new pads? I know its never been an issue with my other cars.

speakermakers

I used a c clamp to push the pistons back into place.

But you did not open the bleeder screw when you did this?

So you pushed the old nasty brake fluid that was in the calipers back into your ABS / Hydraulic unit and into your master cylinder. Could be expensive

Some thing you could check is the pad fitment to the caliper holder, if the pads are binding in the holder it will give you a soft/ spongy pedal feel

Also did you turn the rotors? If you did not then it may take time for the pads to wear into the groves on the rotors from the previous pads

SEA#3

You may have damaged one of the seals in one of the calipers when you pushed the piston back in. I would look for brake fluid leaking around the pistons in the calipers. It may take it a while to show up if rubber boots are good. If this problem was not there when you started then it is most likely caused by something you were working on.

In the Haynes manual it said to remove the cap from the brake reservoir to allow for fluid moving back through the system. I have never heard of opening the bleeder screw when pressing the piston back in, but I have never had this problem before. If fluid moving back through the system can cause damage, what part should I be expecting to replace?

Opening the bleeder screws is a good practice for ABS equipped vehicles. The idea is not to force debris back into the $1000 ABS pump.

 

I don't think that's your problem because you haven't mentioned ABS related codes or problems. I believe if the pump were damaged, the brakes would still work fine. There's something else going on to give you a soft pedal.

If it's not air in the system, it's fluid getting past something or displacing one of the wheel pistons.

I have a similar problem. I one day noticed that my brake pedal bottoms out and the braking is not as good as it should be. Did you ever get the problem resolved?

In the Haynes manual it said to remove the cap from the brake reservoir to allow for fluid moving back through the system. I have never heard of opening the bleeder screw when pressing the piston back in, but I have never had this problem before. If fluid moving back through the system can cause damage, what part should I be expecting to replace?

I have been using a C clamp and pressing them back in for years on many abs and not abs vehicles, I have never had an issue.

I have been using a C clamp and pressing them back in for years on many abs and not abs vehicles, I have never had an issue.

I agree...I've never opened the bleeder screw....opening the cap should be fine...I don't know what 'debris' is going to get into a closed system

 

FWIW, for the pedal to go to the floor of a hydraulic sytem, I'd think you have to have something not sealted properly.....

 

good luck..

I still have not resolved the problem. I have come to the conclusion that I need to replace the master cylinder and see if that helps. I have never had this problem before and nobody seems to know whats up. So I am stuck with randomly replacing parts like a dummy. That’s the part that really burns me, I consider myself a good mechanic. And the brakes worked better before I put new shoes on. Someone mentioned that the seals in the master cylinder could have been damaged, and I think that’s my best shot as of now. Correct me if I am wrong guys but if the problem was in one of the lines then just that wheel would be acting up. Right? I cant get the abs to kick in or the car to skid or anything. All I can do is press it to the floor and hope I stop in time! If anybody can give me any more info my ears are wide open.

I still have not resolved the problem. I have come to the conclusion that I need to replace the master cylinder and see if that helps. I have never had this problem before and nobody seems to know whats up. So I am stuck with randomly replacing parts like a dummy. That’s the part that really burns me, I consider myself a good mechanic. And the brakes worked better before I put new shoes on. Someone mentioned that the seals in the master cylinder could have been damaged, and I think that’s my best shot as of now. Correct me if I am wrong guys but if the problem was in one of the lines then just that wheel would be acting up. Right? I cant get the abs to kick in or the car to skid or anything. All I can do is press it to the floor and hope I stop in time! If anybody can give me any more info my ears are wide open.

Did you bleed the entire system, starting with the wheel farthest from the Master Cylinder?

just get a rebuild kit (should be cheap--at least compared to a whole master cyl)

QUOTE:

Sasquatch: "I don't know what 'debris' is going to get into a closed system"

QUOTE:

Sasquatch: "I don't know what 'debris' is going to get into a closed system"

Okay, so enlighten me...fluid can break down and be less effective but in a closed system, a system w/o seeps to draw in air or dirt, what debris is getting in there?

No disrespect intended.

 

Brake fluid is highy hydroscopic (water loving) and can pick up substantial quantities of water even in a closed brake system. I addition to lowering the boiling point of the brake fluid and causing potential brake failure, the water also corrodes (rusts) the lines and cylinders. All auto manufacturers recommend periodic changes to reduce these possibilities.

 

Even I, in earlier times, used a C clamp and never bled or changed my fluid. Only when the POS AMC calipers froze up did I read and learn the benifits of changing fluid. What I did bleed out was black and full of rust particles. The calipers could not be rebuilt.

 

Opening the bleeder screws is only a precaution when changing pads/shoes as the crap, if any, dosen't stay or travel in the system. Again, you don't want a little spec of rust to screw up an ABS pump, as remote as that may be.

 

Change your fluid every 3 years and you'll spend less on brake hardware in the future.

 

Good luck.

SevenSisters

Well said!

There is also the practice after changing pads of just "pumping up the brakes" all the way to the floor which can cause damage to the seals in the master cylinder, if it's been in service for a while and the fluid hasn't been changed. Also forcing that debris down the line or damage the seals in the master cylinder

Now before you say "I’ve done that 100's of time and never had a problem”. Why not use the information to maybe save yourself some grief in the future

I have

SEA#3

Here's my 2 cents. I do all my own work on my cars. When someone comes to me with a problem like this I have em park it in the dirt and make sure the master cylinder is full. Then just start the car and pump the brakes until you see a drip running down the inside of one of the tires or the bottom of the master cylinder. If that don't work, keep pumping for like 5 minutes and see if you can find the leak.

Perhaps you twisted or stretched a line when you did the pads (I always try to set the loose calipers on top of the rotor). Or maybe what some of the other guys said is right about damaging a caliper. Hope this helps

I did know of the tendency of fluid to attract water (which I believe is why some after market brake systems use different oils in their hydraulic systems). I appreciate you clarification. Specifically though to the question...his brakes were working, he changed the pads, then they aren't working....this wouldn't seem to be due to the break down of his fluid. I am certainly no master mechanic but given that he has already tried to bleed his system there must be a sealant problem no?

The 20% chance goes to piston seals in the caliper.

 

 

After a pad change, the FIRST predal press is likely to go much further than normal and potentially damage the MC piston seals. Bleeding afterward wont rebuild the seal :-(

 

 

Get the wheels off, and make sure the caliper seals are OK, then replace/rebuild the MC, it's the only logical next step. Nothing "dummy" about that :-)

Here's my 2 cents. I do all my own work on my cars. When someone comes to me with a problem like this I have em park it in the dirt and make sure the master cylinder is full. Then just start the car and pump the brakes until you see a drip running down the inside of one of the tires or the bottom of the master cylinder. If that don't work, keep pumping for like 5 minutes and see if you can find the leak.

Perhaps you twisted or stretched a line when you did the pads (I always try to set the loose calipers on top of the rotor). Or maybe what some of the other guys said is right about damaging a caliper. Hope this helps

Good idea about parking in the dirt!! I like it!!

 

I agree about damaging a line when pad were done, could be the issue.