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Re: Brake pedal is very soft and don't work, fluid is...
Another possibility is that the master cylinder had gone bad. There are seals and o-rings in the master cylinder that can wear out or decay over time and this will give a soft or sinking pedal even though the system is intact and not leaking.
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A soft or spongy brake pedal is an indicator that there is air in the hydraulic line(s) of your brake system.
Improper bleeding could be a cause.
Damaged or malfunctioning master cylinder could be another cause...
Damaged, crimped, or pin hole leak in the brake line...
Leaking or damaged wheel cylinder...
Poorly adjusted brake calipers...
Using the wrong type of DOT brake fluid...
Using brake fluid from a previously opened container that has been sitting around for more than 6-months (DOT type 3 and type 4 are glycol-based fluids that absorb water).
You will need to bleed the brake system. I would start with the rear brakes lines and work towards the front.You must have key off engine off when bleeding brakes, apply pressure on brake pedal 10 times and hold. The brake line is now ready to be open. Open and let the stream of fluid come out and close the line tight. Then release brake pedal once bleeder screw is close. This procedure must be repeated twice front and back. After, brakes have been bleed pump the brake pedal before putting in drive. Note: Don't let the resevoir run low on brake fluid. This will cause air bubbles to accumulate on the brake system. Always top off before opening bleeder screw.
You have a leaky brake line somewhere. You will need to find and repair it. If you don't see any lines that are wet, you may have to pull the rear brake drums to check the wheel cylinders. They can also start to leak but are not as likely as a line. If your truck is a standard it's possible that your hydraulic clutch uses the brake master cylinder as a resevoir so check that line as well. A soft pedal would suggest that isn't the problem but if the fluid was low enough air could get into the lines. Hope this helps.
Replace your master cylinder. It is leaking out of the back of the master cylinder and into the booster. If you unbolt the master and carefully look into the booster, chances are you will see brake fluid. Replace it, bleed the entire system, and enjoy your truck again.
There may be air in the lines. Bleed all your brakes starting at the farthest wheel from the resevoir, and finishing at the closest one. Try the pedal after its bled. If the pedal still feels soft or travels to the floor there may be a pinhole leak that may be spraying on the underbody of the car, or the seals in the master cylinder are gone filling the vacuum booster(if equipped). Air compresses more than oil so if bleeding works that may be the problem.
1. I suspect deteriorated brake fluid, some air in the brake lines and tired flexible brake hoses which are past their useful life.
If the brake fluid has not been changed in the past 12 months then have the brakes bled and new DOT 4 spec brake fluid replaced in the system. (Brake fluid must be bled out and changed at least every 2 years). At the same time look for signs of any minor brake fluid leaks or fluid weeping.
2. In a vehicle of that age I would also be replacing all flexible brake hoses before bleeding the brake system again. These flexible hoses deteriorate badly with age and will swell significantly when you apply pressure to them contributing to a soft pedal feel. This is not expensive to have done and, given the safety importance of the braking system, it is imperative to keep the brakes in decent working condition. Ensure you only use very good quality brake hoses. Once the brake hoses are fitted, the brake system is bled and the new brake fluid is added into it at the same time.
With everything tight, new hoses and new fluid in the system you should have a solid pedal assuming everything else is ok. (I doubt that the ABS sensors on your vehicle have anything at all to do with the soft pedal you are concerned about but we cannot test this. It is much more likely that the issue is more fundamental as explained above. On this site we frequently do not have enough information about a vehicle to offer as much information and comment as we would like).
Air in Brake system need to be bled or master-cylinder is BAD. Noise in rear can be alot of different things NOT related to Soft pedal for example bent backing plate,wheel bearing etc. I would recommend removing brake drum and take a look at brakes in the rear contact if you need more help. Good Luck. Thanks for using FIX-YA
Sounds like like you may have air in the hydraulic system.Run some brake fluid through the system by opening the bleeder on the slave cylinder attached to the transmission. Have a helper depress the clutch pedal until it touches the floorboard. Have him tell you so you can close the bleeder.Once the bleeder is closed have your helper push the clutch pedal several times pausing 5 seconds between each push. Keep an eye on the fluid resovoir for the clutch and fill as needed. Do this untill you either remove all the bubbles or the clutch feels good again. It can take a lot of time to move the air down the pipe so be prepared.