Truck smokes if I press the brake pedal when cranking.

[baseballdad]

I have a 2007 Chevy Silverado Classic with the V8. If I press the brake pedal when I crank my truck, it will smoke for about 5 minutes. What would cause it to suck brake fluid into the engine?

[DaveH71]

You mean its smoking out the exhaust when you start it? Are you absolutely sure its only when you press the brake pedal?

 

Have you had to top off your break fluid?

[Chevy Joe]

As Dave said, If it is smoking out the exhaust, the only way I can think of that happening is through the master cylinder vacuum hose that goes to the engine

 

If it is just smoking out from under the hood either the lid for the master cylinder is leaking or one of the brake lines is leaking

 

CAUTION: Don't know if it is still flammable (I am old LOL) but when I was a kid I had an engine fire from brake fluid spraying onto the exhaust manifold

 

Joe

[baseballdad]

It is smoking from the exhaust and only happens if I have my foot on the brake when cranking. I have had to top off the fluid a few times.

[Chevy Joe]

Sounds like seals leaking in master cylinder, then fluid leaking into vacuum booster, then into engine from vacuum hose

 

see diagram below

 

Joe

[DaveH71]

Not very common but it does happen. Time for a new master cylinder.

[BlackZ71Silverado]

Sounds like seals leaking in master cylinder, then fluid leaking into vacuum booster, then into engine from vacuum hose

 

see diagram below

 

Joe

Makes perfect sense due to the pressure created while depressing the pedal.

 

 

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[PJB1972]

Sounds like seals leaking in master cylinder, then fluid leaking into vacuum booster, then into engine from vacuum hose

 

see diagram below

 

Joe

 

+1

[NoProblem]

Try to avoid pushing on the brake peddle when starting.

 

sorry, I had to.

[PJB1972]

This raises a question...

Why doesn't it smoke EVERY time he presses the brake pedal? Like during normal driving.

Does the leak seal once it has vacuum pressure? (i.e. when the engine is running)

[sahls01gmc]

Try to avoid pushing on the brake peddle when starting.

 

sorry, I had to.

Isn't the truck in park when you crank it? Why would press the brake to start the truck?

 

But in all seriousness, your master cylinder needs to be replaced.

[Chevy Joe]

Try to avoid pushing on the brake peddle when starting.

 

sorry, I had to.

 

I was thinking it too LOL !!

 

 

This raises a question...

Why doesn't it smoke EVERY time he presses the brake pedal? Like during normal driving.

Does the leak seal once it has vacuum pressure? (i.e. when the engine is running)

 

I was also wondering about that myself, he said he has only added fluid a few times, wouldn't that seem to say it only sucks fluid on startup? You would think it would need more filling if it was leaking into the vacuum all the time

 

BUT the other point is : what is the fluid doing to the diaphragm, will it casue the diaphragm to fail (like melting it over time)

 

[baseballdad]

Thanks guys. I plan on replacing the master cylinder this weekend.

[Chevy Joe]

Let us know if it stops the problem!!

 

Joe