Brake Booster vs Bleeding Brakes

[BigSlappy]

On my journey of this 1986 GT Vert, I only have 2 things wrong with the car keeping it from drivable, that being steering pump and my brakes. I have the steering pump taken care of, but the brakes im a little confused on. The brakes ONLY work when the pedal is to the ground, but when you jab at the pedal, it will toughen up and brake better. I cant tell if its the brake booster or the brakes needing to be bled. Theres great vacuum going to the brake booster, but I dont know how to test it either than that. Is there a guaranteed way to test it without just dumping money on a new brake booster?

 

[TOOLOW91]

On my journey of this 1986 GT Vert, I only have 2 things wrong with the car keeping it from drivable, that being steering pump and my brakes. I have the steering pump taken care of, but the brakes im a little confused on. The brakes ONLY work when the pedal is to the ground, but when you jab at the pedal, it will toughen up and brake better. I cant tell if its the brake booster or the brakes needing to be bled. Theres great vacuum going to the brake booster, but I dont know how to test it either than that. Is there a guaranteed way to test it without just dumping money on a new brake booster?

Usually a bad booster will be rock solid not sink to the floor . Sounds like a master or air issue in the system

 

[limp]

Have you tried bleeding your brakes or looking for any leaks around the wheels or MC area? No cost to do this....

 

[General karthief]

Ok, a little clarity, when you push on the peddle (engine running) normally, does the peddle go to the floor? If you pump the peddle, not fast, does the peddle get harder? If you pump the peddle a couple times then hold foot pressure, does it slowly sink down?
Look under the master cylinder, is it 'wet' where the MC and the booster bolt together?
Do you hear a whoosh sound when you push on the brake peddle?

 

[Mustang5L5]

If pumping the pedal makes the brakes better, it's a sign there is air in the system somewhere, or one of the hoses is on the verge of exploding due to extreme expansion.

Pushrod adjustment usually creates a similar feeling, but the pedal doesn't build up. Bad booster is usually rock hard pedal.

With the car OFF, pump the pedal a few times to purge out excess vacuum. Now try pressing the pedal. If should be rock hard and not move down much. If it doesn't, you have air, a poorly adjusted pushrod or bad MC or a leak.

 

[BigSlappy]

Have you tried bleeding your brakes or looking for any leaks around the wheels or MC area? No cost to do this....

Im gonna try bleeding the brakes today.

 

[BigSlappy]

Ok, a little clarity, when you push on the peddle (engine running) normally, does the peddle go to the floor? If you pump the peddle, not fast, does the peddle get harder? If you pump the peddle a couple times then hold foot pressure, does it slowly sink down?
Look under the master cylinder, is it 'wet' where the MC and the booster bolt together?
Do you hear a whoosh sound when you push on the brake peddle?

Pedal will go

Have you tried bleeding your brakes or looking for any leaks around the wheels or MC area? No cost to do this....

Over the weekend ill bleed the brakes on it.

 

[BigSlappy]

Ok, a little clarity, when you push on the peddle (engine running) normally, does the peddle go to the floor? If you pump the peddle, not fast, does the peddle get harder? If you pump the peddle a couple times then hold foot pressure, does it slowly sink down?
Look under the master cylinder, is it 'wet' where the MC and the booster bolt together?
Do you hear a whoosh sound when you push on the brake peddle?

When the car is on, the brakes need to be pushed all the way to the ground for them to work. From what I remember, I jabbed the brake a couple times and then it hardened up. Not sure about a wooshing sound. If it helps, it feels exactly like braking a car when its not on and theres no vacuum going to the brake booster. There is vacuum going to the brake booster though, so maybe it would be the MC or a air leak.

 

[General karthief]

Have you done any work to the brake system before this or did you just get this car and this is the way they were when you got it?

 

[BigSlappy]

Have you done any work to the brake system before this or did you just get this car and this is the way they were when you got it?

I have not, but it looks like the past owner did put new brake lines. The car did sit for a couple years, so not sure if that really means anything. The brake pads and rotors are in good shape too.

 

[AeroCoupe]

So if the brakes were fine before and no work that required the hydraulic system to be "opened" has been done since they were good and now the pedal is doing this I would be curious as to how air got into the system. Possibly a failing master cylinder but you should try bleeding the brakes before you jump on the MC being the issue.

 

[Mustang5L5]

. If it helps, it feels exactly like braking a car when its not on and theres no vacuum going to the brake booster. There is vacuum going to the brake booster though, so maybe it would be the MC or a air leak.

If there was no vacuum to the booster, the pedal would be rock hard and barely move. What you are describing is the opposite of how the pedal should feel when the car is not on.

A bad booster, or a vacuum leak would mean the booster is unable to provide assist and the pedal should be hard with no travel at all. You are basically using 100% leg musle to push the MC piston. If it still moves, then you have air or a failing MC or wheel cylinder/caliper or even a leaking brake line. I've even seen seized calipers cause a similar feeling

When you release the pedal, the MC backfills first with fluid from the reservior, before the calipers begin to move to push some fluid back into the cylinder. When you double pump, you are essentially pushing fluid to the calipers, and then taking some more fluid from the MC and pushing it again out to the calipers. Somewhere in your system, there is a gap that requires a lot of fluid to fill. It's either air, or one of the brakes physically has an issue, like a seized caliper pin in the front, that is not allowing the pads to fully close down.

Basically, you need to do a full inspection of all 4 brakes and the lines for leaks and inspect the calipers and wheel cylinders to make sure they are installed correctly. I've seen folks install pads/shoes incorrectly, resulting in poor brake pedal feel. Just because the pads/rotors look good doesn't tell the whole story. Sitting for years can wreck havok on brake systems, especially if the fluid was old and contained a lot of water content.

 

[BigSlappy]

My dad is going to help me out this friday with bleeding the brakes. Sadly dont have one of those self bleeding things lol. Ill do an inspection around seeing how everything looks. I wouldnt be surprised if there is just so much air in the system compared to fluid due to it sitting. Ill update everything this weekend on how it goes.

 

[Mr.Kelley]

Check your rear brake adjustment. Does the parking brake work. If you pull the parking brake does it hit the limit before feeling tight. The parking brake should feel tight before you get 1/2 way on the levers travel. If the parking brake feels loose jack up and support the rear axle and adjust the brakes until they drag a little then try the pedal feel and parking brake feel.

 

[AeroCoupe]

If the car has drum brakes in the rear (good catch Mr.Kelley) go to Post #13 in this thread which shows how they should look when properly installed and it also shows how to adjust them if you do not already know:

https://www.stangnet.com/mustang-forums/threads/drums-catching-pulsing.913806/#post-9210365