Engine accelerates when I step on the brake??

[south280]

Hi, this just started out of nowhere, when I am in neutral (standard shift car) and press on the brake pedal the engine slightly accelerates...   any help would be appreciated. 1968 280sl   Thanks, David

[WRe]

Hi,
I would assume leak air, check vacuum line and check valve from brake booster to intake manifold.
...WRe

[Pawel66]

When you press the brake pedal, brake booster is using vacuum from intake manifold through a hose with a check valve that allows flow in one direction. If booster is air tight, it is "sucked" by vacuum, revs may go slightly up as manifold gets a bit of air from the booster and then back down almost immediately. But if booster is leaking air, it continues giving more air to the manifold - revs just increase just a bit or more, depending on the size of the leak.

[south280]

ok thanks for the info....here is an update...     after the car is running then shut off, I press my foot on the brake pedal and I can hear what sounds like a gush of air from inside the booster itself.  If i press the brake pedal again no sound?     do I need a new booster and if so can I change it myself or is this a big job e.g bleeding breaks etc?

[twistedtree]

New booster, or have it rebuilt.  They aren't hard to remove and replace.