Strange brake problem
Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Strange brake problem
At Sebring yesterday, my brake pedal developed quite a bit of travel all of a sudden.
Brake system is stock calipers, new NAPA front rotors, Hawk HP+ pads with 1 prior track day and minimal street miles, Motul fluid, and Goodridge brake lines (newly installed) with -AN fitting, also shrink tubed. Get this - with the ignition off, the pedal is rock hard as it should be. With the car running, the brakes work, but I can push the pedal all the way to the floor if I try hard enough. No fluid leak anywhere that I can see and I'm certain the brakes are bled correctly (I did it twice with the 2nd time using the ignition off/on/off method so I bled them 3 times in 1 sitting). I'm thinking the brake booster, since when I disconnected the vacuum line, the pedal is rock hard. I tried jamming a 3/8" ratchet extension in there, but I was NOT comfortable with the braking, even though it was rock hard.
Any ideas? Thanks!
Brake system is stock calipers, new NAPA front rotors, Hawk HP+ pads with 1 prior track day and minimal street miles, Motul fluid, and Goodridge brake lines (newly installed) with -AN fitting, also shrink tubed. Get this - with the ignition off, the pedal is rock hard as it should be. With the car running, the brakes work, but I can push the pedal all the way to the floor if I try hard enough. No fluid leak anywhere that I can see and I'm certain the brakes are bled correctly (I did it twice with the 2nd time using the ignition off/on/off method so I bled them 3 times in 1 sitting). I'm thinking the brake booster, since when I disconnected the vacuum line, the pedal is rock hard. I tried jamming a 3/8" ratchet extension in there, but I was NOT comfortable with the braking, even though it was rock hard.
Any ideas? Thanks!
Racer
Joined: Oct 2001
Posts: 304
Likes: 0
From: sometown new york
Re: Strange brake problem (dmtnt)
THis sounds like a master cylinder problem. The fluid is getting past the seals in the MC, that or you got one huge air bubble somewhere. With the car running, you have assist from the booster which would make it much easier to get the pedal to the floor. If the pedal pressure (running and/or not) feels consistant throughout the travel, I'd highly suspect the MC.
Safety Car
Joined: Sep 2001
Posts: 4,411
Likes: 1
From: Wilmington NC
Re: Strange brake problem (dmtnt)
At Sebring yesterday, my brake pedal developed quite a bit of travel all of a sudden.
Brake system is stock calipers, new NAPA front rotors, Hawk HP+ pads with 1 prior track day and minimal street miles, Motul fluid, and Goodridge brake lines (newly installed) with -AN fitting, also shrink tubed. Get this - with the ignition off, the pedal is rock hard as it should be. With the car running, the brakes work, but I can push the pedal all the way to the floor if I try hard enough. No fluid leak anywhere that I can see and I'm certain the brakes are bled correctly (I did it twice with the 2nd time using the ignition off/on/off method so I bled them 3 times in 1 sitting). I'm thinking the brake booster, since when I disconnected the vacuum line, the pedal is rock hard. I tried jamming a 3/8" ratchet extension in there, but I was NOT comfortable with the braking, even though it was rock hard.
Any ideas? Thanks!
Brake system is stock calipers, new NAPA front rotors, Hawk HP+ pads with 1 prior track day and minimal street miles, Motul fluid, and Goodridge brake lines (newly installed) with -AN fitting, also shrink tubed. Get this - with the ignition off, the pedal is rock hard as it should be. With the car running, the brakes work, but I can push the pedal all the way to the floor if I try hard enough. No fluid leak anywhere that I can see and I'm certain the brakes are bled correctly (I did it twice with the 2nd time using the ignition off/on/off method so I bled them 3 times in 1 sitting). I'm thinking the brake booster, since when I disconnected the vacuum line, the pedal is rock hard. I tried jamming a 3/8" ratchet extension in there, but I was NOT comfortable with the braking, even though it was rock hard.
Any ideas? Thanks!
Thw sequence for 2001 up is RR LF LR RF. My guess is you still have air in the system as it is too much of a coincidence to have other things go wrong.
Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Re: Strange brake problem (Richin Chicago)
What brake bleed sequence did you use? If you have a 2001 or later you need to do the channels and not the traditional furthest to closest.
Thw sequence for 2001 up is RR LF LR RF. My guess is you still have air in the system as it is too much of a coincidence to have other things go wrong.
Thw sequence for 2001 up is RR LF LR RF. My guess is you still have air in the system as it is too much of a coincidence to have other things go wrong.
Also, after I bled them, I took the car out to bed the new rotors and the pedal was great so I doubt an air pocket could just appear. Connelly's suggestion of a master cylinder would make sense so I'll start there. Thanks for the advice, guys! :cheers:
Burning Brakes
Joined: Oct 2003
Posts: 826
Likes: 52
From: Chicopee MA
Re: Strange brake problem (dmtnt)
First if you have a bad master cyl it would be bad with or without the engine on or off.Also how is the brakes when you drive with them.Do the brakes apply just after you touch the pedal?Sitting still you can almost push the pedal down all the way on any car while the car is running.The first thing I would do is let the car roll and see how far you push down the brakes before they apply.If it is at the top of the pedal than it is probably alright.
Instructor
Joined: Jun 2002
Posts: 239
Likes: 0
From: Port Orange Fl
Re: Strange brake problem (don7790)
Most likely the master, as a tech, the easyest way to check is when the car is running push the pedal down , light hard light hard, if the pedal goes down, bad master. too bad you couldnt complete the day Joe, it was a blast. ps, my pedal was mushy by the third session, too much heat boiled some fluid. :)
Pro
Joined: Sep 2003
Posts: 731
Likes: 0
From: Calgary Alberta
Re: Strange brake problem (FlamerF1)
Most likely you have air in the master cylinder. However, when you bled the brakes, if you manually bled them and pushed the pedal all the way to the ground during the process it is possible you tore one of the cup seals in the master brake cylinder. Alot of people don't realize with the corvette that you cannot press the brake pedal all the way down during bleeding. The MC cup seals will travel too far out and then tear when they re-insert into the MC.
First check for air in the MC, and do an MC bleed. I believe that there is an MC bleed procedure listed here in the forum how to's.
Good luck.
First check for air in the MC, and do an MC bleed. I believe that there is an MC bleed procedure listed here in the forum how to's.
Good luck.
Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Re: Strange brake problem (hightest)
Alot of people don't realize with the corvette that you cannot press the brake pedal all the way down during bleeding. The MC cup seals will travel too far out and then tear when they re-insert into the MC.
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Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Re: Strange brake problem (FlamerF1)
too bad you couldnt complete the day Joe, it was a blast. ps, my pedal was mushy by the third session, too much heat boiled some fluid. :)
What kind of fluid are you running? Which pads? Any other brake mods?
Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Re: Strange brake problem (dmtnt)
FYI guys, I followed the diagnostic procedure in the service manual and it's conclusion was to replace the vacuum brake booster (as I originally suspected). The procedure was to pump up the brakes with the ignition off, then hold the pedal and start the car. If the brake pedal then depresses considerably under constant pressure (which it did), it says to turn off the car and press the pedal twice. If after the 2nd pump, the pedal is much harder (it was), it says replace the vacuum booster. Looks like a trip to the dealership. :sad: Hopefully there won't be any warranty issues. My service manager there is a really nice guy and I've always tipped him (and the mechanic) well. They did the initial fluid flush to Motul and installed the speedbleeders for me, and never mentioned any warranty repurcussions.
Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Re: Strange brake problem (jleast98)
What would be a good tip for a GM mechanic? Does everyone do this? Just curious.
Intermediate
Joined: Jan 2004
Posts: 25
Likes: 0
From: Concord CA
Re: Strange brake problem (jleast98)
Tips?
Maybe I'm too young, but I've never heard of tiping mechanics.
I guess food service.... auto service.. its all the same kinda deal.
I finally found a good dealership in my area to work with,
after driving to 4 of them. Crown Chevy in Dublin was wonderful!
I guess i should have checked on the forum first :crazy:
but alas it was before i found it.
I was very grateful for their help...
It's standard to tip waiter/ess 10-20% depending on the service,
what would u tip your mechanic? ($5-10 sound alittle low)
then again I live in a upper middle class income area :lol:
Maybe I'm too young, but I've never heard of tiping mechanics.
I guess food service.... auto service.. its all the same kinda deal.
I finally found a good dealership in my area to work with,
after driving to 4 of them. Crown Chevy in Dublin was wonderful!
I guess i should have checked on the forum first :crazy:
but alas it was before i found it.
I was very grateful for their help...
It's standard to tip waiter/ess 10-20% depending on the service,
what would u tip your mechanic? ($5-10 sound alittle low)
then again I live in a upper middle class income area :lol: