New brakes, but still no better at stopping

[dubbsix]

Hey all,

I recently upgarded my brakes with new pads, and rotors, but for some reason i have to literally stomp on the brakes to make them lock up. It almost feels like im not getting enough pressure to the brakes.

The pedal is really stiff and doesnt travel to the floor. Could this be a brake booster problem? If i stand on the brakes while standing still i hear a hissing sound coming from under the dash.

 

[jrichker]

There is no info about your car's model year or mods, which make it hard to tell what's in your car.

Brakes have a number of different possible configurations, so guess work isn't the best method to diagnose problems. What do you have for front calipers, pads, rotors? What M/C and booster do you have? Are your rear brakes disk or drum?

That's why it is a good idea to use the sig under the user control panel (User CP) option. It allows you to post your car year & mods, which help greatly when troubleshooting things. No, it is not there for us to snoop and see any "Secrets" you have hidden away under the hood. Be a good stangnetter and update your sig for future reference & don't keep us guessing.

 

[dubbsix]

This is on a completely stock 89 LX 5.0

The brake pedal is really hard and i get a hissing sound if i just hold my foot on the brake pedal.

 

[bretamo]

Hmmm, could it be the brake booster or vacuum line leak around it?

 

[dubbsix]

Is there a diagram of where all the vac lines go on the mustang?

 

[jrichker]

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

Testing the brake booster
Borrow or buy a vacuum gauge & connect it to the vacuum tree where the booster connects. Start the engine and let it warm up. At idle speed, you should see 16"-19" of vacuum. Increase the engine speed to 1000 RPM and the vacuum will increase slightly, maybe to 18"-21" of vacuum. If you dont have at least 16" of vacuum or more, then you have vacuum problems. The booster needs a minimum of 12"-14" of vacuum or more to work properly.

To test the booster, start the car and let it idle for 2 minutes, then increase the engine speed up to 1000 RPM and hold it for 30 seconds. This gets your vacuum up to it's highest point.

Shut off the engine and press the brake pedal. You should feel some give in the pedal. Repeat the process 3 or 4 times. The pedal should get harder each time. If it does not, the booster is probably bad.

 

[dubbsix]

Thanks for the diagram.

I checked the source hose, and the hose going into the brake booster and they look fine. I took the check valve off and i seem to be able to only blow in one direction.

I dont know if this test will work:
To test the booster, start the car and let it idle for 2 minutes, then increase the engine speed up to 1000 RPM and hold it for 30 seconds. This gets your vacuum up to it's highest point.

Shut off the engine and press the brake pedal. You should feel some give in the pedal. Repeat the process 3 or 4 times. The pedal should get harder each time. If it does not, the booster is probably bad.

Because my pedal is already very stiff and doesnt budge very much. I will try the vacuum gauge and see what the readings are.

 

[90mustangGT]

Did you check the conditon and adjustment of the rear brakes?
- so often overlooked. If the rear are not working properly, the front have to do all the work, reduced braking and reduced life.
- even misadjusted and wrong rear drum function, the drums might still lock up at when you really stomp on it, but durring normal braking they won't be effective.

On the components replaced:

were the pads cracked or the rotors glazed or hotspotted?
- this will tell you they are definatly working, in fact being overworked.

Were both sides in equal condition?
- if one side is doing more braking than the other, you have an issue in the lines, hoses, or calipers.


Brake booster sounds like the issue, but I think this is important to check as well.

 

[dubbsix]

Went i got the car the rear brakes were totally shot and the fronts were glazed over. I replaced the rear and the fronts but now the pedal is just super stiff. When i apply pressure to the brake pedal i get hissing coming from under the dash -- that stops when i take my foot off the brake. I took the grommet and valve out today but they seem to be in good condition -- but just for safe measures i ordered another from ford.

 

[bill302]

Brake Pedal Is Very Hard To Push Down:
The brake pedal requires a lot of force to apply. The pedal is extremely hard and you almost need to use both feet to stop the car. The problem will most likely occur without warning.

Possible causes:
Bad power brake booster: Replace power brake booster.

No vacuum to power brake booster: Inspect and replace vacuum line as required.

Brake line is pinched: Replace brake line.

Kid's toy is stuck under the brake pedal: Remove anything that's under the brake pedal. Insure floor mats are not interfering with pedal movement.


my best guess would be a faulty brake booster....click on link heres a reman booster for $70.00 and there not to difficult to replace. http://www.partsamerica.com/Product...1C&mfrpartnumber=5473207&parttype=250&ptset=A

 

[dubbsix]

Im leaning toward a bad booster since the vac line looks good and the grommet and valved seemed to be in good condition -- although the grommet did have a tear in the outer lip.

 

[robertdale]

I had the same problem with my car. I fixed it by changing all the brake fluid to synthetic DOT 4 fluid. I drained all the lines and pumped the fluid through until it was all clear. It made a night and day difference.

 

[dubbsix]

Roberdale...

So you have a very stiff pedal and a hissing sound coming from the dash?

I thought poor fluid would boil quicker providing horrible stopping power as the temp of the fluid reach boiling.

As it stands now even with the car cold i cant lock up the tires by standing on the brake pedal.. and im a big guy!

 

[jrichker]

Swap the grommet and if that does not fix it, swap the booster.

 

[robertdale]

Roberdale...

So you have a very stiff pedal and a hissing sound coming from the dash?

I thought poor fluid would boil quicker providing horrible stopping power as the temp of the fluid reach boiling.

As it stands now even with the car cold i cant lock up the tires by standing on the brake pedal.. and im a big guy!

I never realy noticed a hissing sound. My pedal was tough. I could push with everything and could not get it to lock up. I'm not sure thats you problem but it will be pretty cheap to try. The fluid should be less that $10 just might take a little time. Also some cheap (Advanced,Autozone) brakes I have been told will cause this. problem.

 

[dubbsix]

Weirdest thing i've ever seen

Okay,

So this morning i figured that im too big to try and remove the booster from the dash myself. I was going to pay a mechanic to do it. I put the check valve, hose and bolts that attach the M.C. back on the booster.

I started the car and i had the same stiff brake pedal. I pumped the brakes with the car off and then started the car. All of a sudden the brake pedal was not so stiff and felt like normal.

I took the car for a spin and the brakes work perfectly! WTF?!

Its working should i leave it as is? Was is possible that something was 'stuck' inside the booster?