Brake booster leaking?

[Pinder]

Im having an issue which I think is a brake booster that has a ruptured diapram. whats a good way to check for sure? Right now if i press the brake pedal at idle the reves go down.

[hauser]

Gernold sent mine off for a rebuild. 

[Tyler S]

You can replace the short section of vacuum hose to the booster with a rubber hose temporarily so as not to damage the reinforced wall during this test.  Then pinch off the hose while the engine is running. There should be no change in idle. Have a helper depress the brake and again pinch off the hose. Again there should be no change in idle rpm. If there is a change then either the diaphragm or plunger is leaking.

[Pinder]

ok ill try that.

[stickandrudderman]

What's to test? If you press your brake pedal and your engine note changes it follows that you must be influencing the mixture by introducing air through a leaking servo.

[Tyler S]

Stick, It rules out an electrical issue with the brake lamps. Have seen a large voltage draw and associated rpm drop from messed up wiring get mistaken for a bad booster. It's just one extra assurance step.

[Peder]

I do also have a problem with the brakes. I have a 1964, and the pedal is very hard to press, and the brakes does not much. When the motor still is cold, the revs goes up to about 1500. But when it is warm, there is no change in the revs. I have changed the vacuum hoses, an I can not herar any hiss (air leak).
I have bought a repair kit from Mercedes, but that was just two small discs.  I have an appointment with a workshop tomorrow.
I also found this at You tube: https://www.youtube.com/watch?v=0sj5d48mcss
Peder

[Pinder]

im pretty sure its toast. Ive seen two types on the internet. One is around $500 and the other is around $110.

when the engine is cold and i press the brakes revs go up. When its hot and I press the brakes the revs go down. Im thinking that car runs rich when cold and about right when warm.

[stickandrudderman]

Stick, It rules out an electrical issue with the brake lamps. Have seen a large voltage draw and associated rpm drop from messed up wiring get mistaken for a bad booster. It's just one extra assurance step.

Well, I suppose that is possible in theory but I would expect such a current draw to reduced the car to a smouldering wreck by that point. Still. never say never!

[Pinder]

Taylor maybe onto something. I do have all the headlamps and tail lights removed.

[Tyler S]

Its just something to consider. Always a good idea to rule everything else completely out. Pinching the hose guarantees a diagnosis.

[Tyler S]

Some parts can't be replaced without sending the unit in. Idle raising when depressing the pedal is usually a leaking differential seal. This seal closes off the port between the front and rear of the large rubber diaphragm.

[Pinder]

Received a brake booster yesterday . Installed it and problem is now resolved. I went with the cheapervunit that rockauto had. Was mostly a straightforward job except the replacement unit hole on one side of the push rod was too small to accept the concentric bolt. Fixed that by reaming the whole larger.