Lost brakes

[JRHS]

Afternoon fellow IdIers,

hope you all feel well and you’re stocked up on toilette paper . I have a little brake trouble and I was hoping you could help figure out how to diagnose the problem , I think it’s related to vacuum. I was backing out of my driveway and the pedal went down to the floor and the brake light came on . I drove it around a little bit and the brakes came back but then went away again a short time after . I’m a beginner wrench turned and am not sure what steps to take to narrow in on the problem . Any help would be much appreciated !

 

[Cubey]

Nope, if the pedal went to the floor, you lost hydraulic pressure. If vacuum was gone, you'd have a hard pedal and you'd have to stomp it with both feet. Check for a blown or damaged hose and leaks at the wheels.

 

[JRHS]

Nope, if the pedal went to the floor, you lost hydraulic pressure. If vacuum was gone, you'd have a hard pedal and you'd have to stomp it with both feet. Check for a blown or damaged hose and leaks at the wheels.

Thanks for the reply I will look for leaks when I get home . I did not not notice any spots on the garage floor but I could have missed something.

 

[Cubey]

Thanks for the reply I will look for leaks when I get home . I did not not notice any spots on the garage floor but I could have missed something.

It could be inside the drum if it was a brake cylinder seal, somewhat hiding it at the tire, so check the back plates at the bottom for brake fluid.

 

[riphip]

More likely vacuum problem. If braking suddenly drops but comes back and then drops, check your vacuum. Tester is about $12. Should hold about 21hg

 

[Black dawg]

It has always been funny to me, but a lot of people describe lack of brake assist as "the pedal went to the floor", I guess because they couldn't push it any farther.


IF the pedal sinks to the floor with little foot pressure, and no leaking brake fluid, master cylinder cup seals are leaking and not applying pressure to calipers or wheel cylinders.

IF pedal gets HARD TO PUSH, it is an assist problem.

 

[Cubey]

It has always been funny to me, but a lot of people describe lack of brake assist as "the pedal went to the floor", I guess because they couldn't push it any farther.


IF the pedal sinks to the floor with little foot pressure, and no leaking brake fluid, master cylinder cup seals are leaking and not applying pressure to calipers or wheel cylinders.

IF pedal gets HARD TO PUSH, it is an assist problem.

Correct!

It might be worth unbolting the MC from the booster and checking for fluid back there, since that could be the source of a leak, dumping it into the booster. It's just 2 nuts; only takes a few minutes to check.

 

[IDIBRONCO]

It's just 2 nuts; only takes a few minutes to check.

You're right. At one time, I was having an awful time getting a good master cylinder for my 1981 F150. I got to the point where I could pull the old one off, bench bleed the new one, and have it installed in less that 20 minutes using only hand tools.

 

[JRHS]

More likely vacuum problem. If braking suddenly drops but comes back and then drops, check your vacuum. Tester is about $12. Should hold about 21hg

Would you test the line going into the brake booster?

 

[Cubey]

Would you test the line going into the brake booster?

You can. Test the pump directly first to get a baseline to go by, then test elsewhere to see how much of a difference there is. There will be some difference, but it shouldn't be drastic, otherwise something is leaking somewhere. The more stuff hooked up, the greater the drain of vacuum. I disconnected my cruise and vac sensor, putting vinyl caps over the barbs on the vac manifold.

 

[JRHS]

You can. Test the pump directly first to get a baseline to go by, then test elsewhere to see how much of a difference there is. There will be some difference, but it shouldn't be drastic, otherwise something is leaking somewhere. The more stuff hooked up, the greater the drain of vacuum. I disconnected my cruise and vac sensor, putting vinyl caps over the barbs on the vac manifold.

Thank you, I just ordered a vacuum tester.

 

[JRHS]

Well the vacuum tester came today and I connected it to the line that goes into the booster . The needle bounced around 21 so I think the vacuum is good . However , with the truck running and the vacuum line disconnected , I was still able to easily push the pedal to the floor . It traveled the whole way with little resistance . Think the booster is bad ?

 

[Cubey]

Well the vacuum tester came today and I connected it to the line that goes into the booster . The needle bounced around 21 so I think the vacuum is good . However , with the truck running and the vacuum line disconnected , I was still able to easily push the pedal to the floor . It traveled the whole way with little resistance . Think the booster is bad ?

If it's not a drastic bounce, it's ok. Directly to the pump should have almost no bounce though since nothing is using it except the gauge. It could a pump getting tired, but I still think your problem is hydraulic, not vacuum.

 

[MtnHaul]

Have you checked the brake fluid level in the master cylinder?

The rear cylinders are relatively inexpensive and easy to replace, at least on a Sterling axle.

 

[JRHS]

Have you checked the brake fluid level in the master cylinder?

The rear cylinders are relatively inexpensive and easy to replace, at least on a Sterling axle.

yes the rear cylinders were replaced by a shop back in November and I don’t see any leaks. I’m going to try and replace the master cylinder tomorrow and see how it goes .