Soft Brake Pedal Help
Thread Starter
Tech Contributor
Joined: Aug 2008
Posts: 2,902
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From: Oak Hill Virginia
Soft Brake Pedal Help
Here's the situation... I had to panic stop tonight to avoid running into someone that pulled out into traffic. 
Immediately after that the pedal went soft and the brakes won't engage until the pedal is 90% of the way to the floor.
Got home, checked for leaks and couldn't find any. Pulled codes and found none. Went to bleed brakes (two-person method) and the rear brakes will not bleed, but the front ones will. Also, with the rear bleeder screws open, the brake pedal will not go to the floor, but it will with the front bleeder screws open.
Anybody have any suggestions as to what I should look at next? 
Immediately after that the pedal went soft and the brakes won't engage until the pedal is 90% of the way to the floor.Got home, checked for leaks and couldn't find any. Pulled codes and found none. Went to bleed brakes (two-person method) and the rear brakes will not bleed, but the front ones will. Also, with the rear bleeder screws open, the brake pedal will not go to the floor, but it will with the front bleeder screws open.
Anybody have any suggestions as to what I should look at next?
Last edited by cdkcorvette7; Jun 24, 2011 at 08:53 AM.
Thread Starter
Tech Contributor
Joined: Aug 2008
Posts: 2,902
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From: Oak Hill Virginia
Road was bone dry. The strangest part to me is that I can't get air or fluid out of the rear bleeder screws but I get all fluid (no air) from the front.
Tech Contributor
Joined: Oct 1999
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From: Charlotte, NC (formerly Endicott, NY)
Sounds like the ABS Modulator isn't allowing any fluid flow to the rear brakes. This may not throw a code. A person on the C6 forums just had something similar happen and it took quite a while to debug the issue. Ended up replacing the BPMV.
Bill
Bill
Thread Starter
Tech Contributor
Joined: Aug 2008
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From: Oak Hill Virginia
I was kind of afraid of that. I'm starting to think that module may be going bad... Today, after the car sat in a hot parking lot for about three hours the problem mysteriously vanished and the brake pedal became very firm and very high, then later after some driving the softness and long travel returned, although not as extreme as it was before.
Any suggestions as to how I might confirm it's the bpmv before I spend a chitload of money on a replacement? I hate just throwing parts at a problem without isolating it first...
Any suggestions as to how I might confirm it's the bpmv before I spend a chitload of money on a replacement? I hate just throwing parts at a problem without isolating it first...
Race Director
Joined: May 2005
Posts: 15,960
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From: West Norriton PA
St. Jude Donor '08
I was kind of afraid of that. I'm starting to think that module may be going bad... Today, after the car sat in a hot parking lot for about three hours the problem mysteriously vanished and the brake pedal became very firm and very high, then later after some driving the softness and long travel returned, although not as extreme as it was before.
Any suggestions as to how I might confirm it's the bpmv before I spend a chitload of money on a replacement? I hate just throwing parts at a problem without isolating it first...
Any suggestions as to how I might confirm it's the bpmv before I spend a chitload of money on a replacement? I hate just throwing parts at a problem without isolating it first...
Get with someone that has a Tech2 and do the automated brake bleed procedure.
That will let you know if the pump is shot.
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From: California
Just a guess here. But it could just be in the master cylinder. The piston in there that moves when you step on brakes works front and back brakes as separate systems. It could be the seal for the rear went bad when you made the hard stop. Would also explain why you can't bleed rear. A rebuild kit or a new master cylinder might be all you need.
Thread Starter
Tech Contributor
Joined: Aug 2008
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From: Oak Hill Virginia
Just a guess here. But it could just be in the master cylinder. The piston in there that moves when you step on brakes works front and back brakes as separate systems. It could be the seal for the rear went bad when you made the hard stop. Would also explain why you can't bleed rear. A rebuild kit or a new master cylinder might be all you need.
Race Director
Joined: May 2005
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From: West Norriton PA
St. Jude Donor '08
I have a Tech2 and I'm sure some of the shops around your way do too.
It's a really easy procedure to perform and should take less than an hour.
Just put it on a lift, take off the tires and run the procedure.
Heck of a lot better than a pump and cost of installation. Where is Oak Hill, VA ? Is it close to Washington, DC ?
It's a really easy procedure to perform and should take less than an hour.
Just put it on a lift, take off the tires and run the procedure.
Heck of a lot better than a pump and cost of installation. Where is Oak Hill, VA ? Is it close to Washington, DC ?
Thread Starter
Tech Contributor
Joined: Aug 2008
Posts: 2,902
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From: Oak Hill Virginia
I have a Tech2 and I'm sure some of the shops around your way do too.
It's a really easy procedure to perform and should take less than an hour.
Just put it on a lift, take off the tires and run the procedure.
Heck of a lot better than a pump and cost of installation. Where is Oak Hill, VA ? Is it close to Washington, DC ?
It's a really easy procedure to perform and should take less than an hour.
Just put it on a lift, take off the tires and run the procedure.
Heck of a lot better than a pump and cost of installation. Where is Oak Hill, VA ? Is it close to Washington, DC ?
Race Director
Joined: May 2005
Posts: 15,960
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From: West Norriton PA
St. Jude Donor '08
My brother lives in the DC Area and might be coming up this weekend, I could send hom home with mine.
I've only seen one brake master cylinder go bad on a C5 and it totally failed, (i.e. No Pedal at all). Luckily it happened right in front of my house ( I live on a dead end street).
Ended up replacing it and running the automated bleed procedure.
Have you tried the gravity method. Crack open your rear bleeders with the car jacked up ( higher in the front) and see if you're getting any fluid.
I've only seen one brake master cylinder go bad on a C5 and it totally failed, (i.e. No Pedal at all). Luckily it happened right in front of my house ( I live on a dead end street).
Ended up replacing it and running the automated bleed procedure.
Have you tried the gravity method. Crack open your rear bleeders with the car jacked up ( higher in the front) and see if you're getting any fluid.
Thread Starter
Tech Contributor
Joined: Aug 2008
Posts: 2,902
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From: Oak Hill Virginia
My brother lives in the DC Area and might be coming up this weekend, I could send hom home with mine.
I've only seen one brake master cylinder go bad on a C5 and it totally failed, (i.e. No Pedal at all). Luckily it happened right in front of my house ( I live on a dead end street).
Ended up replacing it and running the automated bleed procedure.
Have you tried the gravity method. Crack open your rear bleeders with the car jacked up ( higher in the front) and see if you're getting any fluid.
I've only seen one brake master cylinder go bad on a C5 and it totally failed, (i.e. No Pedal at all). Luckily it happened right in front of my house ( I live on a dead end street).
Ended up replacing it and running the automated bleed procedure.
Have you tried the gravity method. Crack open your rear bleeders with the car jacked up ( higher in the front) and see if you're getting any fluid.
I had the car level with all four wheels off when I tried bleeding the brakes; I could try it again with the front higher later today. When I cracked the bleeder screws there was some fluid present, but there was not enough pressure when the brake pedal was depressed to cause any to shoot out...
Also, when I drove the car again this morning the problem had "magically" disappeared again. Right now the brake pedal is very firm and very high. Maybe I have a poltergeist living in my engine bay screwing around with the brake lines while I'm not looking
Race Director
Joined: May 2005
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From: West Norriton PA
St. Jude Donor '08
Maybe you have an air pocket. You could try re-bleeding them again.
Then take the car out and stomp on the brake pedal to activate ABS and try bleeding again. You may have some air bubbles in the ABS Block, that can only be bleed out via activation or the automated bleed procedure.
Then take the car out and stomp on the brake pedal to activate ABS and try bleeding again. You may have some air bubbles in the ABS Block, that can only be bleed out via activation or the automated bleed procedure.
Thread Starter
Tech Contributor
Joined: Aug 2008
Posts: 2,902
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From: Oak Hill Virginia
Maybe you have an air pocket. You could try re-bleeding them again.
Then take the car out and stomp on the brake pedal to activate ABS and try bleeding again. You may have some air bubbles in the ABS Block, that can only be bleed out via activation or the automated bleed procedure.
Then take the car out and stomp on the brake pedal to activate ABS and try bleeding again. You may have some air bubbles in the ABS Block, that can only be bleed out via activation or the automated bleed procedure.
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From: Dyer, IN
Le Mans Master
Joined: Dec 2006
Posts: 7,251
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From: Phoenix Arizona
Here's the situation... I had to panic stop tonight to avoid running into someone that pulled out into traffic. Immediately after that the pedal went soft and the brakes won't engage until the pedal is 90% of the way to the floor.
Got home, checked for leaks and couldn't find any. Pulled codes and found none. Went to bleed brakes (two-person method) and the rear brakes will not bleed, but the front ones will. Also, with the rear bleeder screws open, the brake pedal will not go to the floor, but it will with the front bleeder screws open. Checked EXTENSIVELY for leaks and found none. Anybody have any suggestions as to what I should look at next?
Immediately after that the pedal went soft and the brakes won't engage until the pedal is 90% of the way to the floor.Got home, checked for leaks and couldn't find any. Pulled codes and found none. Went to bleed brakes (two-person method) and the rear brakes will not bleed, but the front ones will. Also, with the rear bleeder screws open, the brake pedal will not go to the floor, but it will with the front bleeder screws open. Checked EXTENSIVELY for leaks and found none.
Anybody have any suggestions as to what I should look at next? 
take it to a good mechanic.fyi this is NOT ICE MODE !
believe me i know! 
Thread Starter
Tech Contributor
Joined: Aug 2008
Posts: 2,902
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From: Oak Hill Virginia
Le Mans Master
Joined: Dec 2006
Posts: 7,251
Likes: 16
From: Phoenix Arizona