Brakes Brake Pedal Hits Floor Before It Slows

dnbonds · Jan 5, 2014

First off, the brake pedal makes a hiss sound similar to exhaling really loud. It was like that when I got my fox 3 months ago. However, it didn't take too much pressure on the pedal before the brakes started working. Just today after driving on the interstate the brakes feel like they are completely shot. It makes an even louder hiss sound and it has to hit the floor before it even starts to slow down. It scared me to death when it first started on an exit ramp.

I went to the nearest autozone and popped the hood to check the master cylinder. It was lower than the Min so I went inside and got some Prestone Dot 3 brake fluid to top it off. That being done, it still has the same issue. I pumped the brakes for a minute or two and checked the master cylinder again but it was full. So I went about my daily business knowing my brakes were bad and drove far enough back that I wouldn't rear end anyone.

What could be the cause of this happening? I replaced the brake pads and shoes when I first got my fox. I'm getting my brake lines bled and my front struts put on this Wednesday. Can't do them myself because I don't have a garage and it's colder than Antarctica lol.

I need to know what I might need so I can get it all done this Wednesday.

Thanks in advanced!

2000xp8 · Jan 5, 2014

Why were you getting your brake lines bled in the first place?

Regardless, sounds like the MC to me, the person bleeding them should be able to easily figure it out and the fox MC should be readily available.

dnbonds · Jan 5, 2014

The reasons I was getting them bled were:
- Hissing/Spongy Brake Pedal which I already described
- Vibrating while applying brakes
- Pulling towards the left or right when stopping at a red light

I figured I might as well get them bled since I've read it sometimes fixes the spongy pedal. Any ideas on the hissing though? It doesn't sound like it's coming from the MC, more like from the pedal assembly itself.

89oem · Jan 5, 2014

Brakes are single most important system in your car. The left / right flutter could be anything from worn ball joints to calipers to the MC.

Your car has a master cylinder to pump the fluid to its calipers but is assisted by a vacuum driven Brake Booster. A hiss indicates a vacuum leak. It could be the seals in the booster, the vacuum line feeding it or the vacuum check valve. You can pull the vacuum line from the tee and blow into it.. IIRC it will not allow air to pass so you should feel the resistance, you can also dtermine if the line leaks, if the seals are shot its shot..

Vacuum leaks typically have additional performance issues, idle, heater on but not opening vents etc

It could also be the gaskets in the MC as 2000xp8 indicated.

Hard to tell without seeing it.

My option, let the brake guys diagnose it and fix it correctly. Then you can drive with confidence. Boosters are readily available and you google it to get cost ideas but under $150.

MC on left Booster on Right.
Generic photo....your MC will plastic with a black cap on it....

2000xp8 · Jan 5, 2014

dnbonds said:
The reasons I was getting them bled were:
- Hissing/Spongy Brake Pedal which I already described
- Vibrating while applying brakes
- Pulling towards the left or right when stopping at a red light

I figured I might as well get them bled since I've read it sometimes fixes the spongy pedal. Any ideas on the hissing though? It doesn't sound like it's coming from the MC, more like from the pedal assembly itself.

Hope you got a few bucks to spare for this work.
Sounds like your bill is going to be alot more than shocks and bleeding.
You could be looking at, ball joints, tie rods, rotors, more pads etc.

Booster could be bad too, but i'm pretty sure the booster just assists with the braking, so i don't think the pedal would goto the floor and you possibly have some idling issues because of vacuum leak a bad booster can cause.
Then again, i've never had a booster go bad so i could be wrong.

If the brakes need bleeding, there is a problem. It's not really general maintainence.

dnbonds · Jan 5, 2014

He is actually a family friend who works on our vehicles when we don't have the equipment to do it ourselves. He's doing the struts for me because I am not able to, and he is doing the brake lines because it is way too cold for me since I don't have a garage. I'll be there the entire time, mainly to inspect if I need any serious suspension work. Thanks for the info. If he does not have any available, would these be best? If I have to replace them I might as well not do the bleeding yet.

http://www.latemodelrestoration.com/item/LRS-2140C/1987-93-Mustang-Brake-Master-Cylinder-For-23L-50L
http://www.latemodelrestoration.com...oster-Also-Fits-83-93-Mustang-23L-Convertible

I never had any issues idling. It's normally a constant 700 to 1000 RPM without any bouncing. 1k When I first start it and 700 when I am stopped at a light.

89oem · Jan 5, 2014

What 2000xp8 said. MC most likely.... and in my experience the brake cylinders in the rear drums leaking.... MC Local parts store Autozone, Advance etc. about $50. If it doesn't steer on its own your ball joints should be fine..... If MC when you hit he brakes you can almost hear the gush as the plunger passes through the leaky MC seals.... Your friend will know all this.

dnbonds · Jan 5, 2014

Ok thanks for the information guys! Atleast I have an idea of what is going on come Wednesday

Mustang5L5 · Jan 5, 2014

Assuming stock brakes?

Hissing noise couple potentially be a vacuum leak in the booster.

As for pedal to the floor, that's potentially a failing MC.

All this assumes you haven't replaced the stock components with aftermarket brake systems or brakes off SN95s and such.

89oem · Jan 5, 2014

Hey one last thing, I was driving home in this foggy Stephen King type weather and got to thinking, you said you changed your brakes, did you turn your rotors? You may just have brake shimmy from warped or worn rotors..... At least you'll really know your brake system by the end of the week...

dnbonds · Jan 5, 2014

I only changed the pads and shoes with autozone's duralast. I didnt turn the rotors or anything. It is a completely stock setup although I may go and rip the axles off a thunderbird coupe and swap my drums out. When I first got my fox, someone didn't put the drums together right and all of the springs were broke. Went and got a whole drum rebuild kit and made sure it was correct. What a pain drums are....

If I am getting new rotors would you guys recommend autozone's or something from LMR or AmericanMuscle? I'm not looking to make huge HP gains so I am not looking at high-end rotors or brakes. I do, however, want to get rid of those drums >.>

dnbonds · Jan 10, 2014

Apparently the rear drums were not adjusted correctly. My fox stops better than it did before but still retains a soft pedal with a little puff of air when I first start driving. I'll probably end up getting new brake lines along with a new MC and Booster in a few months just so I am fully comfortable driving with a brand new brake system.

Brakes Brake Pedal Hits Floor Before It Slows

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