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I have opel.corsa 1.4 GLS .After many days I drive my car but due to Brake jam while starting I can't move the car .With the engine off, in neutral, if I jack a front wheel up and rotate the wheel by hand, it turns freely.and if I then start the engine in neutral I cant rotate the front wheel

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  • Welcome to the site, what year is your corsa?
    – George
    Nov 17 '20 at 9:38
  • When you start the engine, does the brake pedal go down without pressing it?
    – HandyHowie
    Nov 17 '20 at 11:49
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I'm not entirely sure if this issue can be caused by other brake parts such as the ABS module, but in this answer I've formulated what seems to me the most logical explenation. These are my thoughts:

Your car has a brake booster which uses vacuum pressure from the intake to amplify the force applied to reduce the efford needed from the driver to stop the car. See below image.

Brake booster diagram

(Source: https://www.researchgate.net/figure/Diagram-of-vacuum-booster-system_fig3_326618599)

The left chamber and right chamber both have vacuum pressure inside. Between these chambers there is a flexible diaphragm. When the brake pedal is pushed, atmospheric pressure is introduced in the left chamber, which pushes the diaphgram into the right chamber because of the pressure difference. This way the pressure in the brake pedal is amplified using the vacuum pressure in the right chamber.

Now if there is a leak in the left chamber, there is always a pressure difference that causes the master cylinder to be compressed. As a result of which the brakes get jammed on when the engine is started.

As per @GdD's comment: You can test this by removing the vacuum hose that attaches to the vacuum source (see image). If the brakes don't stick on anymore, here is your problem. The solution is to rebuild or replace the brake booster.

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  • @TANKEEN, you can test this by pulling the vacuum line off of the brake assist, plugging the hose and running the engine. If the wheel spins then that's the issue, if not it's something else.
    – GdD
    Nov 17 '20 at 8:13
  • @GdD good addition, updated my answer, thanks!
    – user60481
    Nov 17 '20 at 8:22

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