Brake pedal goes to floor w/ engine on.

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

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.

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.

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

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.

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

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.

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

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.

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.

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?

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

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

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

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.

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

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

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.

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

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..

Change abs system if you have one

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

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

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

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

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.

78 corvette guy.......your rear caplipers have two bleeders inside and outside.......make sure you do both. I've seen people try to do just one......that's not good enough to get a "pedal" that won't sink.

Calipers may be on wrong side. If bleeder is at the bottom it's wrong. They have to be at the top

I did all the rest and it did NOT work. The pushrod you need to adjust is the one on the rear side of the booster. You need to remove the M/C, measure the depth of the master cylinder cup at the front and then set the rod that comes out of the back of the booster to have about .25 inch clearance from the M/C cub bottom. It worked for me.

Don't have the answer but,this might help. No one stated how they checked for leaks on fittings. My dad always told me to use dish soap on bleeder valves and then check for bubbles and on master cylinder fittings also hoses going to caliper for leaks. P.s. also read your master cylinder instructions on how to adjust its rod for proper length, this makes a big difference.

Hi all, So I had this same problem with my ep91 starlet and this is what I had done, Brake was fine, but when I turned car on, it went to the floor. Not completely, but off the floor about 10 cm, I had spent months working on it and I sware I almost pulled all my hair out, and ended up looking like good ol'Homer J. So this is all what I did I had replaced; Master cylinder Brake booster Gaskets Wheel boosters Adjusted my rear drum brakes with the adjusters Replaced all pads and discs Checked vacuum pressure, all normal no loss Crimped brake lines to check pressure behind my boosters, no loss. Made new friends, the owner of the wreckers, both ones in town lol. And the answer was something soo simple, my brain overlooked it for thinking it could not be the problem. Adjust your hand brake line, fixed all my problems lol.

Did anyone try my solution of adjusting the rod that goes from the booster to the master cylinder and how did it work out.

Adjusting the rod is only performed if buying a new or refurbished power booster to be installed with the old master cylinder. If installing a new master cylinder with the old booster the only measurements to be accomplished is to micro the old and new master cylinders surfaces to make sure are the same. If not then the old power booster in the car the rod need adjustment according to the taken measurements from the master cylinder. Back to the pedal issue a possibility is air still trapped in the lines, proportioning valve or even the ABS accumulator or maybe the new master cylinder to be installed failed from the bench bleeding procedure or after installation. New cars are more difficult to troubleshoot than the old since there are additional components in the brake system. Hope this help in understading troubleshooting before spending a lot of $$$

I installed a new M/C and booster and I had the classic no pedal when I started the car. I adjusted the rod coming out of the booster to the master cylinder. I left about a 25 thousandth clearance . Put it all together and now I have a brake pedal when the engine runs. Could be witchcraft but......................................

Did anybody ever solve this problem? My 1988 Fiero GT has the same issue. No fluid leaks, rebuilt master cylinder, good calipers, good flex lines. Could a bad brake booster cause this symptom?

Hey FieroGR, I had the similar problem with my EP-91 starlet, I did boosters and master cylinder, including all seals, did vac tests which all came back perfect, I crimped rear lines to check to little leaks. I replaced all wheel boosters, drum shoes, discs. I ended up becoming best mates with the mechanics at the wreckers I had spent so much, he had finnaly figured it all out, it ended up being my hand brake tensioner lol. Had him look at it, fixed it and now brakes are perfect. Sometimes the simplest things we over look, as we feel it is not worth our time to investigate them lol.

One more person with the same mystery problem. I replced the MC and bled the air out. Bled the brake lines twice and pedal still goes to floor. Booster checks out OK on pedal test. Not sure how adjusting parking brake cable would help problem of brake pedal going to floor. Hoping to find mystery solution.

Problem solved. It was actually the power brake booster. I installed a remanufactured unit from Cardone and voila, I have a pedal that no longer sinks.

Had the same symptoms after replacing rear breaks after a failed cylinder bled the lines empty. Bled over half a gallon of brake fluid starting farthest back and working closer, replaced master cylinder, bench bled, installed and bled the system again. Brakes went to the floor when 05 Blazer was started. Turns out I had the calipers switched and the bleeders were at the bottom of the caliper instead of the top, so air was trapped above the bleeders. Switched calipers, bled again and problem solved.

Every time I get through bleeding, bench bled the new master cylinder, bled at the proportion alve,bled all the wheel cylinders and calipers,both gravity bled and with a helper has no booster,as soon as I start rolling the pedal goes to the floor,you can pump it up.then next time you start to use them,pump them up again,

Check for bad hub / wheel bearings will cause brake pedal to go to floor if one or both are loose.

I don't know if this will help but my Tahoe did the EXACT same thing. I finally fixed it. Every time I bled the master cylinder, I then bled each wheel like you supposed to do. Didn't help. Today I bled the master cylinder and nothing else. Brakes are perfect now. Somehow, air was getting in line when bleeding at each wheel even though did correctly. It's an old vehicle but it DID work!

I found on my 76 Stingray that the rotors were not true and they pushed the caliper pistons in and out and pulled air past the seals. No fluid leaks but after 150 to 200 miles had no brakes. Chaged master cylinder and stilll had the problem. Change the rotors and front calipers and that fixed it.

I am having the same problem with this Hyundai HD65 truck. changed the M/C and wheel cylinders and bled but when the engine is started the paddle has no pressure at all and it goes to the floor. I have bled the brakes again and again but still the same. I am planing to blank of the rear wheel cylinders and check the front cylinder pressure and then the rear ones to see exactly where I'm loosing pressure. If I get results I will post

I had the same problem with my Subaru. While it was not running, brakes were firm. Once car was cranked, brakes would depress to floor. Changed ABS, master cylinder, brakes and rotors. Found the bracket on the back of the caliber was stuck and could not release. Replaced and everything works well. Good luck

I have a 1996 Corvette, I have breaks when I start it up, however when I press them down to stop and after a few seconds it goes to the floor. I have replaced the master cylinder, checked lines for leaks, checked all wheels and bled the breaks like the factory suggested. Still did not fix the problem. Any suggestions???

Check your ABS system/box.

Hello, I had the same problem with a 1988 Fiero GT. I changed the master cylinder and even rebuilt the new one, but to no avail. Also changed out the proportioning valve - no luck. The calipers, brake lines and bleeders were all good. So I thought maybe it was the booster - despite various websites saying it couldn't possibly be a booster problem. Well, it was the Booster. Replaced it with a unit from Rockauto and brakes operate like new.

Thanks, I will do that. I have tried everything else

I have a 74 corvette replaced master cylinder bench bleed. Replaced all calipers and still spongy breaks. I have ran about half gallon of break fluid no leaks see no air. Anyone have any advice.

I have the same problem with Elantra 2011 I replaced rotors and pads and master brake And the booster it works for month and the problem returned back the same. I think it is ABS problem If i can make it not working to try the pedal Without the ABS to watch the difference

It IS a power booster problem. I literally just had the same issue on my 2008 Taurus. Have since changed the booster and have no issues.

Had a 1975 vett come into my shop ans very soft spongy pedal. did a complete inspection and found no leaks. Owner said he never added fluid either. bled the brakes and got air out of the rear right caliper. Pedal was good and hard. next week he is back with the same problem. Again got air out of right rear. Rebleed and told him if it happened again we would need a caliper replaced. His friends said I was ripping him off. Came back a couple months later with same problem. Replaced the caliper with a condition if the problem returned he would get a full refund. came back a couple of weeks later to say thanks. The caliper apparently let air in at rest but under pressure it sealed up tight.

Have a 75 Corvette with the same problem... not yet solved. I believe I may be having the same problem with rebuilt calibers at rest and or on brake pedal return sucking air back into the piston. The air bubbles keep comming and comming and yet I have no fluid leaks anywhere. I doubt its the booster where as if the booster is not working you will have an un boosted MC and a hard pedal. The push rod consists of an inner and outer steel rod. Therefore you have a full steel rod linkage from the pedal to the master cylinder.

75 Corvette......I find that extreme care is needed when replacing the brake pads if you force them in between the rotor and the pistons you can damage the lip seal if the piston is not true to the cylinder walls of the caliber. You should not see any brake fluid come out of the piston boot when you are finished.