Brake pedal falls to floor at when sitting in traffic

[seotaji]

When pulling out of the driveway or slowing down in traffic, the pedal is fine. When sitting at a light, the pedal will drop to the floor and I'll have to push harder to stop the car from rolling.

I have no idea if this has any bearing on the problem, but the rear calipers make a clicking noise when I apply the brakes. I can only guess that it's b/c the caliper slides need lube.

Have the cups in the master cylinder gone bad or did I introduce air into the system when bleeding the brakes?

Fluid is new (flushed it a few months ago), but the old stuff was in since it was new (9 years). Didn't have a problem until recently.

I don't have the time to replace it myself, so I'll most likely pay the dealer to do it, if the MC is indeed the problem.

Is there any test I can do with my limited abilities that will prove conclusively that something is the problem?

Thanks in advance.

 

[punisher]

From the info you posted, a master cylinder is a pretty good bet to be the cause of your problem. The only other thing that comes to mind is a bypassing ABS valve block (if the car has ABS). Only ran into that once in 15 years in the shop though.

Any other component would be leaking fluid externally (or into the brake booster) to cause the symptoms you describe and cause a noticable brake fluid loss to boot.

 

[Greaser]

Master Cylinder is shot

 

[Mud]

Air in the lines usually causes a spongy or low pedal, but not a sinking pedal.

A bad vacuum booster would cause a hard pedal.

If the ABS was messed up , you would have a dash light on to indicate a malfunction. The brakes would still work, just no anti-lock function.

To me it sounds like the valve inside the MC is leaking internally and letting fluid back through the front/rear brake ports and therefore back into the bowls. All this is not an external leak and you will not see fluid dripping anywhere.

I suspect that the MC should be replaced.

PS - this assumes that there are no leaks at calipers/wheel cylinders. Those are sometimes hard to spot.

 

[labman]

Unless you have been adding fluid to replace what leaked, it is the MC. Changing brake fluid is no substitute for replacing old, worn rubber parts.

 

[medic]

Sounds like a leak to me.

 

[tom slick]

I had exactly the same problem. MC is done.

 

[Gary Allan]

Yep, if you can get brakes with pumping them up ..and there is no fluid lose ....MC.

 

[labman]

It is an easy job to screw up, but not too bad with good instructions, at least a Chiltons, the Fram of manuals. I have done almost nothing the last 25 years without a real shop manual.

 

[seotaji]

Well I just found out that I'll have 2 days off next week, so I wonder if tackling this job myself is a good idea?

It should just be remove and replace right?

It would be a good time to replace the fuel filter while I'm in there.

Or should I just have someone else do it?

I'm sure it'll be a $400 job considering that the MC itself is over $150 retail.

[ April 22, 2005, 12:33 PM: Message edited by: seotaji ]