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under the hood on the driver side in front of the brake booster
I believe that is called the power brake booster
NO! They did not have a code box until 1989 Yes they all do. The code box is right in front of the brake booster in the engine compartment on the drivers inner fender well. There is a tester there and a series of blinking lights basically. You will need a manual to decipher the number of blinks.
Un-plug the vacuum hose going to the booster, If the brakes work the same, as before unplugging the hose, it's shot.
It is the same as the brake reservoir. You should see a line heading from that to the clutch master cylinder. Cheers.
brake booster has probably gone bad.
I don't really understand what you want to know so I'll take a shot in the dark here and try to help you out the best I can with information you've given, (lol - none). The purpose of the check valve is to give you some power assist by holding the vacumn in the booster if the vehicle shuts down to give you some braking ability. Should hiss with enging running when unplugged from the booster. If unplugged from the hose with the vehicle off it should retain a vacumn in the booster. Booster problems (hard pedal) are sometimes caused by brake fluid leaking from the rear seal on the master into the booster and damaging the rubber inside. Look for fluid drip or peeling paint down the face of the booster, and remove the two nuts and pull the master away from the booster and visually check for wetness at the seal. Replace with a used/new one if needed but if you go for a used booster check it first. If it's a check valve you need, a parts supplier will have it or get one from the dealer. Some people recommend replacing master & booster as a unit but on and older vehicle if it's still o/k I'd only change whats needed.
in your tranny fluid check tube you will need a funnel
How to Install Front Brake Pads Check Related links below.
check your fuse and your brake light switch on your brake pedal lever.
Check for a brake light fuse
The recommended spark plug gap for a 1987 Volvo (all models) is .028"