Can low brake fluid cause brakes to go to the floor?

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SaxAndLiz

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Two days ago, my wife said she was having trouble braking and the brakes were traveling to the floor. When I tested the brakes yesterday, the brakes worked fine about half the time, and went to the floor the rest of the time.

The brake fluid level is just below the minimum line. There are no leaks in the brake lines and near bleeder valves as far as I can ascertain. The brake malfunction light has been coming on intermittently for months. I thought it was associated with the e-brake only, and I now know it serves a dual purpose.

I am trying to figure out if it’s the master brake cylinder for sure or something else is up. I ran full ODBC diagnostics using BlueDriver and got zero codes back. Thanks!
 
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SaxAndLiz said:
Two days ago, my wife said she was having trouble braking and the brakes were traveling to the floor. When I tested the brakes yesterday, the brakes worked fine about half the time, and went to the floor the rest of the time.

The brake fluid level is just below the minimum line. There are no leaks in the brake lines and near bleeder valves as far as I can ascertain. The brake malfunction light has been coming on intermittently for months. I thought it was associated with the e-brake only, and I now know it serves a dual purpose.

I am trying to figure out if it’s the master brake cylinder for sure or something else is up. I ran full ODBC diagnostics using BlueDriver and got zero codes back. Thanks!
Click to expand...
If you have no external leaks then I would be willing to bet it's the master cylinder. As you seem to have discovered the brake light on the instrument panel also comes on for low fluid.
 
Are there any other tests I can do? I was thinking of topping off and bleeding the brakes. I know a bad master cylinder can cause the problem intermittently. Just hate throwing parts at a problem without being sure.
 
SaxAndLiz said:
Are there any other tests I can do? I was thinking of topping off and bleeding the brakes. I know a bad master cylinder can cause the problem intermittently. Just hate throwing parts at a problem without being sure.
Click to expand...
According to the FSM these are the following causes of a low or spongy brake pedal:
1) Fluid leaks
2) Air in system
3) Piston seals
4) Rear brake shoe clearance out of adjustment
5) Faulty master cylinder
6) Booster push rod out of adjustment

You've confirmed there's no external leaks which eliminates 1 and 3. Air in the system (99 percent of the time) does not cause an intermittent low brake pedal so 2 is out. Rear brake shoe clearance out of adjustment and booster push rod out of adjustment also don't cause an intermittent low brake pedal so 4 and 6 are out as well. That just leaves 5. Faulty master cylinder.

If you replace the master cylinder make sure to bleed the master cylinder per the factory service manual instructions. If you don't you'll have a bad pedal again.
 
Low level is also an indication of worn pads or shoes.

When you said no leaks did you remove the rear brake drums and look at the wheel cylinders?

Did you look in the narrow gap between the gas tank where the brake line is hidden?

What year do you have?


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19963.4lsr5 said:
Low level is also an indication of worn pads or shoes.

…
What year do you have?


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Click to expand...

1999, 239 K miles.

I installed new pads on the rear drum pads recently, and the front ones were good too. No, I didn’t look inside the drums, but I will do that. The lines looked good inside the engine bay.
 
SaxAndLiz said:
1999, 239 K miles.

I installed new pads on the rear drum pads recently, and the front ones were good too. No, I didn’t look inside the drums, but I will do that. The lines looked good inside the engine bay.
Click to expand...


They usually rust where you can’t see them and rain doesn’t rinse the dirt and salt. Look at the gas tank for a wet spot on the inner frame rail.


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Since you've recently done brake work I would definitely pull the rear drums and inspect for "workmanship". Also, if you did'nt pull the front apart to inspect the pads I would do it, sometimes a visual inspection when still assembled can be deceiving. Ask me how I know!
 
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