Brake pedal goes to floor w/ engine on.

185

Asked by Sep 14, 2015 at 11:16 AM about the 1980 Chevrolet Corvette Base

Question type: Maintenance & Repair

When the engine is started the brake pedal goes almost to the floor, will not stop car.
1) No fluid leaks
2) Changed master cylinder, bled system several times.
3) Hoses, lines, pads - OK
4) Replaced power brake booster check valve and filter.
5) Engine has good vacuum and idle.
Is it possible for a caliper to leak in air without leaking fluid? If so how do I figure out which one? A bad power brake booster failure usually means a hard pedal, but is there something I'm missing.
thanks

28 Answers

121,285

The fluid is going somewhere? and its going into the booster...

4 people found this helpful.
19,855

Check the fluid level. Is it still full? Air in the system. Low on fluid? May be air in the system and it is working out, or there is a leak. Do a physical inspection of all connections and new parts connections. Check lines for leaks or cracks. Some times hands on feeling or a clean rag can be used to find any fluid leaks. How soon after the brake job did the peddle go to the floor? Was this a do it yourself project? If it was at a business, take it back if it was resent. Did you use the correct fluid? If air is getting into the system, it will also push out fluid under pressure. If a caliper is leaking, you will notice fluid and the pads will be wet or coated. If it is a "I did it myself, perhaps a trip to a shop to do a check up and system bleed is money well spent. Less than the deductible after an accident.

5 people found this helpful.
185

Thanks for your quick replies. The fluid is topped off and never goes down. There were no leaks. If it were going into the booster I'd loose it in the master. It's a new master cylinder. I've owned and worked on this car for 30 years, never took it to a business, would have to tow it. Calipers are dry. When I bled the calipers I had a good steady flow w/o bubbles. Pedal feels good until engine is started.

8 people found this helpful.
22,320

Is there a rod adjustment on the brake booster. Rod may have to be adjusted if it does has to be screwed out.

2 people found this helpful.
185

Thanks firebird336! I wish it were that easy. The car had been sitting for months and I can't think of a reason that rod would need adjusting. I wish I found a leak, I'd have it fixed.

22,320

Did you replace the brake booster or just the check valve ? May have to replace brake booster.

1 people found this helpful.
185

Only the check valve. Everything that I've read plus people I've spoken with think the booster is not at fault. My understanding is a bad booster will make the pedal harder not go to the floor. It is 35 years old, Thanks.

1 people found this helpful.
80

I am having the same issue with my 78 corvette. New master (bench bled) new caliper due to the old one leaking. I have no leaks and get a great pedal, until I start the car, then it goes to the floor. I have gone through 2 quarts of brake fluid bleeding them. Did you ever find and answer? Kenney D

7 people found this helpful.
22,320

Recheck caliper slide pins making sure they are not seized up and also check for loose wheel bearings. Jack vehicle up and let wheels hang then grab top and bottom of tire and pull in and out making sure wheel is tight.

19,855

You have a vehicle that has a lot of go to it, and with that comes the need for a lot of stop. Don't mess with the breaks, take it to a professional shop and have them go through it and make it right. Yes it will cost a bit of money but I bet it will cost a lot less in the long run than the insurance deductible for a clash and insurance rate increase for three years. You may have a bubble of air in the system or even a slight leak that will not allow it to seal under operating pressure. Don't mess around. You did the heave expensive work, keep your Corvette looking sharp and accident free. (experience talking here.) No wreaks, but some white knuckle driving ONCE.

2 people found this helpful.
80

The professional shop charged me $80 to bleed the system. Told me he didnt need to remove the rear tires to bleed them. And told me there was only one bleeder on each caliper. PLUS, I left with no brakes for $80. Since then I borrowed a vacuum bleeder. It draws fluid from all the calipers but the left rear. (Though pump and bleed works on that caliper) Could it be a collapsed line, or maybe the proportion valve?

1 people found this helpful.
80

Oh, and the vacuum is not losing pressure when the bleeder is opened

19,855

I was thinking the proportioning valve. If you don't get any break fluid from the one rear caliper, what did the shop bleed?

2 people found this helpful.
80

The shop was useless. If I pump the brakes fluid will come out of that bleeder. But when I try to vacuum bleed that leader, nothing will come out

19,855

It sounds like you may have some rust or sludge in the line that a heavy pull on the break fluid causes it to block the line. the splitter may be a good place to start. Have it pulled off and then air blow the line to make sure it is clear. It is a lot of work we all know, but a crash due to bad brakes really sucks and makes for a bummer of a day.

2 people found this helpful.
20

Kinda same problem with my 82 Chevy custom deluxe 20 I'm working on right now. I'm looking on here to find an answer for my break problems. I just bought this truck, its been converted into a dump truck with a 1 ton duel axel under it. It's been setting for years and I had to replace a caliper, 2 lines and the master cylinder.. Bleed the brakes with the help of my wife, who's leg is worn out now lol, but had pedal after bleeding the front, but after trying to Bleed the back the pedal went to the floor and won't come back up? Trying bleeding the front again and still no pedal. Need help please and thank you. Josh

2 people found this helpful.
20

For some reason probably a safety in the corvette, the engine has to be running while bleeding the brakes

1 people found this helpful.
20

I have a Kia pride with the same problem. I wish you guys find the answer still now i'm looking for a solution for this problem.

1 people found this helpful.
20

It is your check valve or your power brake booster. I would start by replacing the vacum check valve

1 people found this helpful.
20

I'm not so sure for the brake booster is too old and rusty, well better to replace it. but not so sure if it works after, I'll let you know..

1 people found this helpful.

Change abs system if you have one

20

Did any one find the answer to the problem of the pedal going to the floor when the engine is started

2 people found this helpful.

Hm I am having an issue with my EP91 starlet. Firm brakes when not on, once started up brakes go to the floor

20

SOMEONE MADE THE SUGGESTION TO LOOK INTO THE ADJUSTMENT THAT GOES INTO THE BOOSTER. ANOTHER SUGGESTION WAS DISCONNECT YOUR VACUUM TO THE BOOSTER AND CAP IT AND SEE IF YOUR BRAKES WORK WHEN YOU START THE CAR. ALSO WHILE YOU HAVE THE VACUUM OFF CHECK IT TO SEE HOW MUCH VACUUM YOU HAVE AND IS IT SUFFICIENT. I HAVE BEEN TOO BUSY TO TRY ANY OF THESE BUT IF YOU TRY ANY AND THEY WORK, PLEASE LET ME KNOW.

Ok please help me out. My pedal goes to the floor and maybe the last inch it starts to grab. I have replaced everything. Booster, master cylinder, poportioning valve all 4 calipers pads and rotors.ive even adjusted the brake booster push rod. I’ve bleed my truck so many times but it still goes to the floor. No leaks

20

WATCH THIS YOU TUBE AND SEE IF IT APPLIES Be patient it is very thorough. https://youtu.be/rYYzPIGoxfY Power Brake Booster Test URL Good URL but does not cover “Brake pedal; goes to floor when starting the car” The PBB rod should be about 0.25 mm from the MC socket bottom To test the PB Vacuum valve: 1.Remove it and suck on the pipe (vacuum) side and if you hear hissing- all is well 2.Blow into the pipe (vacuum) side and you should not be able to blow into it. Good Luck

20

Bronco Just as an aside, I sent the above note on the You Tube MC. I have not tried it as I only found it the other day. I have a problem with my brake pedal goes to the floor when I start the car. I disconnected the booster and plugged the vacuum hose which has about 21" of vacuum at idle. I found that my brake pedal stayed firm when I started the car without the booster. That leads me to think my problem is in the booster rod adjustments. If anyone has gone further than I have and been successful PLEASE let us know.=

Hey guys I just did a rebuild on a 66 Charger and I'm having the exact same issue. My braking system is all 100% new. I've even adjusted the push rod and all that did for me was to shorten the distance the pedal went to the floor but still only gave me 2-3 in of movement of the pedal and no additional stopping power.

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