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Q: brake sinking but still work.

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please bare with me since my English is not quite good. when car is off brake is really firm. but when starting to drive brake lose pressure but only sometime. also lose pressure when at a hill. but will stop the truck before the brake pedal hit the floor. little bit dangerous cause it work perfect sometime and other time the brake pedal will sink and surprise me

My car has 180000 miles.
My car has a manual transmission.

Hello there, a few different faults can cause the vehicle to have poor brake performance like this. The most common causes would be the brake booster, brake master cylinder, or a brake fluid leak.

When a truck has this sort of braking issue it is recommended to not drive the vehicle, as it is unsafe until the problem is resolved. A qualified technician will be able to diagnose your brake system if you’d like to get this fixed. Once this is done, an accurate repair can then be made.

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