What would cause the brake pedal to go all the way to the floor?

ALAAL

MEMBER
2004 CHEVROLET VENTURE
82,000 MILES

My 2007 Chevy van had a dead battery this AM. I tried to jump start the 2007 with the 2004. After about 30 seconds, the cables started smoking so I unhooked the cables. The cables were hooked up: red to red, black on 2007 to black on battery & black on 2004 to engine block bolt. After removing the cables the 2004 sounded "funny", like it was idling low. I got in to move it & the brake pedal went to the floor. I had to pump the pedal to get it to stop. No lights or "check engine" on, starts up normal but still sounds "funny". Any ideas on: why the brakes don't work & why did the cables start smoking? Thanks in advance.

6 Replies

KHLOW2008

MECHANIC
41,814 POSTS

The cables started smoking because they were subjected to excessive cranking time which would heat them up and the main reason is becaus they are of low capacity. A better set of cables would not have such occurrence.

If the brake pedal is still going to the floor, you most probably have a failed master cylinder.

With engine running, depress and hold the brake pedal lightly but with sufficient force to allow the pedal to sink if it occurs. If the pedal sinks after a few seconds, either the master cylinder is bad or you have a leak somewhere.

If the battery was completely drained prior to the jump start, the low idling would occur as the computer has lost its memory and would require some running time for it to relearn and run correctly again.

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Sunday, November 20th, 2011 AT 4:57 AM

ALAAL

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To clarify: Prior to trying to jump start the 07 van, the brakes were functioning properly on the o4 including when pulling the 04 over to the 07 to jump start. I'm thinking there is something electrical involved that was "shorted" during the jump start process. What on the 04 Venture brakes is electrical? Also, the cables, although not heavy duty are medium duty & have been used to jump start autos & even a back *** without any problems previously. Could a shorted cell in the 07 battery cause a short circuit that led to the smoking/too hot to touch cables? Since no "check engine" lights or other electrical items in the 04 seem to be affected, can the computer be checked for codes? Thanks again.

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Sunday, November 20th, 2011 AT 1:46 PM

ALAAL

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Also, the cables were only connected for about a minute, maybe less. When I turned the key on the 07 to try to start it didn't even turn over. I cut off the key & got out immediately & that's when I saw the smoke coming up from the cables (both at the 04 & the 07). Thanks.

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Sunday, November 20th, 2011 AT 1:48 PM

KHLOW2008

MECHANIC
41,814 POSTS

The brakes are hudraylics and the only component that is electrical would be the anti-locking brake system.

From symptom description of the cables, it should not be a fault with the battry but could possibly be due to the starter not returning after starting. Was there any abnormal noises?

Computer can be checked for codes even if the MIL is not indicating.

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Sunday, November 20th, 2011 AT 9:01 PM

ALAAL

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Thanks for your help KHLow2008. Replaced the master cylinder, bled the lines, & everything is back to normal. Guess it was just a coincidence with the battery thing. Low brake fluid light is now & won't go off. Fluid is at max after bleeding. Tried pumping the pedal 3 times in 5 secs & taking loose the positive cable but still on. Any ideas?