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Dabees0 · Joined: 06 Apr 2018 Posts: 3

I have a 55 2nd series truck with 383 and camaro front clip. Front disc rear drum setup.

Truck runs great but after a few minutes of driving, when I stop at a light or stop sign the motor starts revving up about 500rpm or more. Once I let off brake and start rolling it goes back to normal or if I put it in neutral it will settle down. It only does this when brake is applied.

Any thoughts or experience with this?

acardon · Posted: Sat Aug 04, 2018 3:09 pm Post subject:

Do you have a power brake booster? Look for a vacuum leak at the booster or a bad valve in the booster. Try temporairly plugging the vacuum line to the booster.

Dabees0 · Joined: 06 Apr 2018 Posts: 3

Thank you for the response.

I do have a power brake booster. It’s a 7 inch single diaphragm which I would like to switch out for an 8 inch dual diaphragm

How can I check to see if there is a bad valve?
The hard part with this issue is that it only does it when I’m driving and then come to a stop. It hasn’t done it when car is in park so I don’t know if plugging the line will show me if it has a leak.

acardon · Posted: Sat Aug 04, 2018 4:11 pm Post subject:

You will still have brakes when you plug the vacuum line to the booster. Just have to push harder.
Another possibility would be soft motor mounts causing the throttle linkage to change from the motor shifting.