shadowgriffen

the strangest thing happened this morning (I assume brake master cylinder)

I got into the car and drove away to work as usual, but when I got to the stoplight my brake pedal went all the way down towards the floor almost making me hit the person already at the light!

now mind you, they have always been hard as a rock, so I always assumed that perhaps I was in need of a new master cylinder...I have no idea whats going on.

my car still stops, but it is really strange that all-of-a-sudden my brakes are buttery smooth and the pedal goes all the way down to the floor before the brakes kick in.

Any input guys?? I would appreciate it.

shdoug

I agree with the master cylinder hypothesis. It's strange that it wouldn't do it every time, though. I assume the fluid level looks good?

shadowgriffen

I hear you...

Yes it's full

help!

bjay51d

I had that same thing happen to me when i first purchased the car.The pedal was really stiff.Then out of the blue it went down to the floor.It turned out to be two frozen rear calipers.I had the fluid flushed and the lines & calipers replaced and havent had a problem since.

marco402

sometimes a piece of rust (or such) in the mstr cyl plunger will leave a gap in one of the o-rings, allow fluid bypass...OR (scary thought) primary shuttle valve in ABS stuck momentarily.....mstr cyl rebuild is cheaper....but the fact that fluid is full rules out wheel caliper issue....have you done any recent work on the brakes, leaving an air pocket?

marco402

bjay51 has a good point, are you frozen (literally) up there?

bjay51d

I wasnt talking literally frozen just rusted...Wow didntt even know that was possible.

marco402

he has been driving his car for awhile, so i imagine a frozen/rusty caliper would have shown itself earlier, but i see that the weather has been really cold, and upstate NY is under a mile of snow , but if it's below freezing and the brakes were wet last night, the first stop could be a long one

bjay51d

He said they were always stiff.I drove my car for a while before the brake failed.I see your point it has been cold as ***** out this way.

shadowgriffen

Mind you, my fluid was full last week, when I cheked it when I got to work it was halfway empty, I have not checked it today, will update.

Yes, we have had no day over 10 degrees Farenheight. windchill is at minus 15 F.

correct, my brakes have always been stiff, since I bought the car almost five years ago.

One thing: about two months ago, to anwser marco's original question, I replaced the rear brake pads. Two days before replacing them my brakes did the same thing they are doing now, but with a LOUD screech, really scary actually.

today my brakes continue to be buttery soft and just glide their way to the very end, where pedal meets the metal

very strange....and I dont want to put anyone in danger.

bjay51d

exactly what happened to me...I wouldnt drive it anymore...get to a shop.youre boiling your fluid.pretty soon it wont stop at all.

shadowgriffen

ummmm...jay, I think you duplicated my post by accident.

check your PM inbox.

bjay51d

I got alittle ahead of myself

shadowgriffen

well my brake fluid is fine, so I'm not burning any brake fluid I just ran upstairs to the garage and checked, its all there.


this is driving me

bjay51d

Get your brakes checked asap.That loud screech was a warning.

lkchris

Over the years I've had two master cylinder failures, both easily associated with sudden cold weather. Shrinking rubber, I expect.

shadowgriffen

Negative my friend, you missunderstood my post.


I stated that the same buttery soft feeling has happened to me before, but LAST time that happened to me my brakes were making horrible squeeling noises, this time it's buttery soft sans screech.

marco402

soft pedal that almost goes down to floor, no unusual noise, full of fluid, very cold weather......COLd (read HARD) o-rings in mastercyl, allowing fluid bypass, not dumping it, but letting it squeeze by....did you say once stopped, the pedal will hold the car at a stop?

shadowgriffen

Yes, that is correct.

mgw_300e

Did you ever get this figured out?

shadowgriffen

Negative, but now that it;s not as cold as it's been lately the brakes feel about 85 percent normal

I'm 100% certain it's the master cylinder.

rokacook

My 1995 E420 is doing the exact same thing. I replaced Pads and bled system, am pretty sure the master cylinder is bad. I did also notice the ASR light comes on after a few minutes and the ABS pump quiets down at the same exact moment. I am going to replace master cylinder next and see if light goes out in conjunction with the replacing of Master cylinder.

rokacook

Replaced Master cylinder , no preesuse at rear brake bled valve, I have brakes and ASR light is still on after ABS pump stops after 2 minutes or so the braking seems fine but noisy ABS pump and ASR light on I wonder if ASR pump is bad below master cylinder a little electric motor and pump one line to ABS system, Is there any good writting as to how this entire system works so that I could understand and troubleshoot?

rokacook

As it turned out it was the rubber o ring that seats into reservoir was leaking. all better.