josephqatarcarguy 3 Report post Posted June 6, 2019 the brakes on my 1970 mustang completely failed while driving... power brakes, disk in front and drums rear... it was working fine but while driving last night slowly faded and just completely stopped working ... no visible leaks, brake fluid level not low ...but there is a hissing sound now every time you press/pump on the brake pedal where do i start? Quote Share this post Link to post Share on other sites
Ridge Runner 1,113 Report post Posted June 6, 2019 Booster diaphram blew out ,or the rear seal on the booster 1 RPM reacted to this Quote Share this post Link to post Share on other sites
josephqatarcarguy 3 Report post Posted June 6, 2019 7 hours ago, Ridge Runner said: Booster diaphram blew out ,or the rear seal on the booster but the brake pedal does not stick and feels like the booster gone?master cylinder? Quote Share this post Link to post Share on other sites
Ridge Runner 1,113 Report post Posted June 6, 2019 Yes ,the pedal will not stick ,you loose vacuum at the booster and that would be the hissing you hear Quote Share this post Link to post Share on other sites
skidmarky 50 Report post Posted June 6, 2019 I agree the booster is shot, but the brakes should still work, just no power assist. Quote Share this post Link to post Share on other sites
1969_Mach1 333 Report post Posted June 6, 2019 19 hours ago, josephqatarcarguy said: the brakes on my 1970 mustang completely failed while driving... power brakes, disk in front and drums rear... it was working fine but while driving last night slowly faded and just completely stopped working ... no visible leaks, brake fluid level not low ...but there is a hissing sound now every time you press/pump on the brake pedal where do i start? What does "slowly faded and completely stopped working" mean? Pedal went to the floor? If that's the case then look at the master cylinder if there are no external leaks. It might be leaking internally. Or, it was slowly more difficult to push the pedal? In that case, like others mentioned, look at the brake booster. But, with a bad booster the brakes should still work, just extremely difficult to press the pedal, like skidmarky mentioned. Quote Share this post Link to post Share on other sites
Midlife 814 Report post Posted June 6, 2019 Another possibility is a ballooning brake line, which meets all of the symptoms described. Quote Share this post Link to post Share on other sites
josephqatarcarguy 3 Report post Posted June 7, 2019 15 hours ago, 1969_Mach1 said: What does "slowly faded and completely stopped working" mean? Pedal went to the floor? If that's the case then look at the master cylinder if there are no external leaks. It might be leaking internally. Or, it was slowly more difficult to push the pedal? In that case, like others mentioned, look at the brake booster. But, with a bad booster the brakes should still work, just extremely difficult to press the pedal, like skidmarky mentioned. the brakes got weaker...had to pump the brake pedal and actually stop the car Quote Share this post Link to post Share on other sites
1969_Mach1 333 Report post Posted June 7, 2019 From the description I'd think there is a brake fluid leak somewhere or the master cylinder is bad (leaking internally). Make certain to pull the rear wheels and brake drums and check the wheel cylinders for leaks. Sometimes the brake dust and brake shoes will absorb a lot of fluid from a leaking wheel cylinder before you see fluid on the ground. The hissing sound is from the brake booster. I don't have a lot of brake booster experience. It may be just starting to leak vacuum. But, typically if the booster is leaking vacuum the motor should run rougher when you hear that noise. How does the motor run when you hear the that noise? Quote Share this post Link to post Share on other sites
josephqatarcarguy 3 Report post Posted June 8, 2019 it looks like the master and booster is shot ... im not sure if the car came with power brakes or a conversion kit was installed. the car has many mods done it by the previous owner.. 351c, c6 trans..... is there any way i can be sure which booster and master i should get? will part https://www.summitracing.com/int/par...0206/overview/ fit? whats in the car now looks similar ... same pedal etc i ve attached the marti report of the car. Quote Share this post Link to post Share on other sites
