1957 T-Bird Engine Accelerates When Brake Pedal Depressed

[TJShea]

This one has me stumped. I have had this car for a few weeks. When Ii apply the brake the engine RPMs increase. I have read manuals, forums and I have yet to see this as a subject. I have a 312, automatic trans with factory power brakes. Does anyone have an answer why this could be happening? I have never experienced a car engine increasing RPMs when a brake is applied, especially in an automatic.

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[Dave H]

Shot in the dark here. Assuming that you brake with your right foot, are you certain that you're not accidentally applying a little throttle pressure with the outside of your foot when you brake? Although I can't say I've experienced this in my '57, I have discovered that it's easy to do in a couple of my other vehicles, if I'm not careful.

If this isn't the answer, I can't help any further.

 

[thessler]

My guess is you have a hole in the brake power booster diaphragm. Easy to check, disconnect vacuum hose to power booster and plug. Start car and step on the brake I'll bet the idle doesn't go up. If that's the case you need to have power booster rebuilt.
Just a thought, Tom

 

[Dale Leonard]

I agree with Thessler

 

[rich s]

This one has me stumped. I have had this car for a few weeks. When Ii apply the brake the engine RPMs increase. I have read manuals, forums and I have yet to see this as a subject. I have a 312, automatic trans with factory power brakes. Does anyone have an answer why this could be happening? I have never experienced a car engine increasing RPMs when a brake is applied, especially in an automatic.

Check out the power brake booster diaphragm and check valve, a slight increase in RPM may be due to a vacuum leak,
easiest way to check is remove the vacuum hose at booster end and plug it. If the problem goes away the power brake booster and or hose has a vacuum
leak. parts are readily available and its an easy to rebuild part

 

[Jim Ray]

I have a 55 and it may have a different booster setup than a 57, but mine did that and I replaced the filter on the booster. It is a sponge filter similar to a lawnmower filter and held in by a round spring clip. Adjacent to the firewall. I made a filter and it works fine

 

[TJShea]

Thanks for the suggestions and insights. I will take a close look at the brake booster