1994 C1500- Brake Pedal to Floor

1994 Chevy C1500 pickup- 157,000 miles

I was driving home from work last week, and had to stop for a red light. It caught me a little by surprise, and I had to brake firmly, but I didn't slam on the pedal.
I felt the normal pressure in the pedal, but it soon gave way and fell to the floor. The brake [(P)(!)] light turned on. (At this point I pulled the parking brake release, and was surprised to hear it actually release, as if it didnt release fully when I started off from work.) The rest of the way home, I increased my following distance and used careful downshifting (5-speed) to baby the brakes as much as possible.

I thought one of the brakes lines had blown, but I checked all over, front and rear and inbetween- no leaks. I even pulled the wheels off and checked the front calipers, rear cylinders, and fittings. I don't see any leaks whatsoever, and there is plenty of brake fluid in the reservoir.
Now, everything is back to normal. The pedal has normal pressure, and the brake warning light has gone out.
What happened?

EDIT:
When using the parking brake to park the truck, the light [(P)(!)] used to come on. It doesn't now. Is this related? I can tell the bulb is fine when I start the truck.

Since you say the brake level is OK in the master cylinder, then I would say with almost 100% certainty that the master cylinder is bad. In the old days we would perform a simple test: hold a light, steady pressure on the brake pedal and if the pedal slowly goes down, it means the seals inside the MC are leaking and the MC needs to be overhauled or replaced.

I would get a new MC on there right away. This situation sounds VERY dangerous.

So, I just lightly apply brake pressure with the engine running, and feel for the pedal to find its way back to the floor again? I just want to make sure I'm doing this test right...

For the past week, the problem has not returned, and I was wondering if there could have been a small air bubble in the line somewhere; maybe it finally worked itself to the reservoir? At any rate, it totally feels like normal now, and has successfully tricked me into driving it like nothing's wrong anymore.

i would still put a maste rcylender on it because you'll have brakes then the next time you wont. so i say this it will save you a wreck in the long run.

So, I just lightly apply brake pressure with the engine running, and feel for the pedal to find its way back to the floor again? I just want to make sure I'm doing this test right...

For the past week, the problem has not returned, and I was wondering if there could have been a small air bubble in the line somewhere; maybe it finally worked itself to the reservoir? At any rate, it totally feels like normal now, and has successfully tricked me into driving it like nothing's wrong anymore.


Yes, engine running or off doesn't really matter too much. Just hold constant pressure and see if the pedal slowly goes down.

But I must say, from your initial description, it sounds EXACTLY like a bad MC. They are pretty inexpensive to buy. I would not take the chance. I would install a new (or reconditioned) MC in there right away.

Good luck and stay safe.

And what qualifies me to make this diagnosis? See below, yes, it's from 1971.......
http://csgbenefits.org/Delco_Brake_Cert.jpg


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Always err on the side of safety with brakes and most definitely replace the M/C.

A buddy couldn't stop his hod rod truck at a car show and got lucky by not hitting any of the other show cars. We told him we'd get it home on a car trailer. He declined after the brakes felt good that same day. 2 months later he smacked his garage door pretty good (pedal went to the floor). That was 3 yrs ago and a new M/C, been good since.

If you decide to stick with what you've got, thinking it was just an anomaly, I sure do hope your not behind me when the light turns red!!

[quote=Urambo Tauro;6796075]1994 Chevy C1500 pickup- 157,000 miles

I was driving home from work last week, and had to stop for a red light. It caught me a little by surprise, and I had to brake firmly, but I didn't slam on the pedal. [Quote]


the master cylinder does not fail this way . most often the pedal when pressed firmly WILL slowly fall to the floor.

since this is a 1994 I highly suspect the ABS module/pump assy as your componet that caused this. especially with the given conditions that were present when this occured.

these GM ABS units in this vintage year have been reported for failures all over the internet. do a search you will learn how to bypass this unit.

This is a work truck, not my own. The company just isn't going to throw parts at something that is working fine right now.

Now, I put my foot on the pedal the other morning while parked, but it really didn't seem to creep down. I had to drive it again today, and it still has no problems. I'm going to try the pedal again, after a day of driving, and see if the temperature makes a difference.

The theory I had about an air bubble in the line, eventually working itself out to the reservoir-- Is that possible? Can it happen?

This is a work truck, not my own. The company just isn't going to throw parts at something that is working fine right now.

Now, I put my foot on the pedal the other morning while parked, but it really didn't seem to creep down. I had to drive it again today, and it still has no problems. I'm going to try the pedal again, after a day of driving, and see if the temperature makes a difference.

The theory I had about an air bubble in the line, eventually working itself out to the reservoir-- Is that possible? Can it happen?

with this info its looking even more , like the ABS is , the componet causing this. when you drive this WORK TRUCK keep a greater distance to the vehicles your following.

1994 truck used in a business ? must be scraping bottom..

LOL
I know, I know. Oldest truck in the fleet; the others are mostly 2003s and 2004s, racking up the miles. They have issues of their own.

I didn't drive it today, but expect to next week. I don't recall it having ABS, but I'll take a closer look on Monday.

had a simular problem my slef, turned out to be some air that had worked its way down the line, have you tried re-bleading the lines? if its that easy and cheep fix.

I has same problem with 1990 pickup. Replaced everything and bleeded system over&over. Master cylinder, booster, lines, cylinders, calipers. Ended up being ABS modulator to rear ABS leaking during hard breaking causing pedal to floor when needed most. Replaced it from autozone less 150$ and no more problems. :)

Check yours (ABS modulator) and bleed it too--it has own bleed screw.

See if pedal improves. Also black dirty brake fluid is sign of plunger rubber wear in system--mine had this.

Thanks, I'll mention it to my supervisor. It hasn't acted up since, brake-wise. It's not being driven right now until it gets new motor mounts (right one went, and the engine is leaning over, real close to the battery+ cable going to the starter).