Why won't my rear disc brakes keep a pedal - 1997 Mercury Mystique

Pedal, not peddle. First make sure reservoir is full at the brake master cylinder. Then check your brake pads (for disc brakes) and/or brake shoes (for drum brakes). When the pads or shoes are very worn down, you will get a low pedal. If you have disc brakes on the front and drums on the rear wheels, first try just replacing the front brake pads. If you get a good pedal after the front is done, many people tend to let the rear brake shoes go unless they are making noise. These systems are designed to put most of the braking force on the front discs, so the rear shoes do not need changing as often.

Michael:

You must start bleeding the brakes at the wheel farthest from the master cylinder (usually the right rear), then the next farthest from the master cylinder, then the next, then the closest. If your master cylinder is at the left front of the car, start with the right rear, then the left rear, then the right front, then the left front. If you don't bleed the brakes in the correct order, you are just shifting the air in the lines from one line to another. Make sure that you close the bleeder before letting the brake pedal up, and the engine should not be running when you bleed the brakes... Make sure that the emergency brake is off. Make sure that the master cylinder does not run out of brake fluid at any time that you are bleeding the brakes.

If it has rear disc brakes just keep pressing the e brake pedal down and releasing it to adjust.

Hi oakleafwoodw, sounds as if the brake master cylinder has busted a seal allowing the brake fluid to leak by cylinder when you push the brake pedal giving you no or very little pedal pressure....it is located under the hood on the drivers side firewall, you will see all the brake lines attached to it , remove those and the two bolts holding it on,take it with you to auto parts store for a rebuilt one , they will keep your core for rebuilding, other wise you pay a core charge., verify that they have the one you need before hand, get a quart of dot 4 brake fluid, hook it up, and bleed air from the brake lines starting with wheel cylinders in this order Right rear......left rear.....right front.....left front...making sure to keep fluid level topped off in the master cylinder during the whole bleeding process or you will pump air into lines....OK!! caution: you should not drive it until you have good brakes!! you said they still work but if you had to stop suddenly ,it won't do it.

your rear brakes are worn or the self adjusters are rusted, assuming you have drum rear brakes & not disc pads in the rear.
Try backing up several times with very hard stops to activate the self adjusters. If you don't back up much, the self adjusters can not work. Parking brake will be adjusted at the same time.

please rate.

Hi,
sound as if you really do have a problem!
From your description I presume that you are confident in doing your own work?
The quickest way to check your system is to use brake hose clamps to isolate each section of the braking system. I would suggest that you rent or buy a set of the clamps.

Put the truck on axle stands and make sure it's safely secured. ]
If possible have an assistant to sit in the cab and depress the brake pedal on your instructions.
Place a brake hose clamp on both front brake hoses and the rear axle hose.
Depress the brake pedal firmly.
The pedal should have minimum movement, and be rock-solid and you should not be able to depress it further.
If the pedal does go down when you apply it, the likely reason is that the Brake Master Cyl is by-passing internally, ie, only one section is active.

You stated that the M/C had been replaced. so we shall presume that the brake pedal is rock hard.
Go to the rear brake hose clamp and release it. Instruct your assistant to depress the brake pedal. If the brake pedal moves a significant distance, then (a) your rear brake shoes require adjustment (b) rhere is a leaking brake cyl, (check for brake fluid in the drum) or (c) you have a "lazy' or a piston (s) which have siezed during a brake actuation. That problem will require removing the rear brake drums for further inspection. Not the problem? Then adjust the rear brakes if required, then depress the brake pedal again. The downward travel should now be noticeably reduced.

If all is well at the rear brakes. refit the brake hose clamp. Go to the passengers side front brake and have your assistant apply the footbrake. Pedal rockhard/minimun movement? Release the brake hose clamp whilst your assist has pressure on the pedal. spin the front wheel by hand, and note if (a) the brake pedal has excessive downward travel. (b) the brake pads are contacting the brake disc, (the wheel will cease rotating and you will hear the pads contact the disc.)

Pedal displays limited downward travel and pads contact disc? Refit the brake hose clamp and go to drivers side brake and follow the same procedure. If the pedal has excessive downward travel then you have found your inital problem.

If releasing both front brake hose clamps results in excessive brake pedal travel, then the problem will be easier to address if you deal with one side first, complete the resolution, test by using the brake hose clamps, then start / complete the other faulty brake.

Whichever side you start to work on, be methodical, boring as it sounds.
remove the road wheel, but before doing so, place a hand on the top and bottom of the tyre and rock the wheel away from you and check the bearing play. If memory serves me correctly, that year Dodge has the discs in one piece with the hub.

You have removed the wheel. Now, have your assistant turn the steering onto full right lock. Before continuing, I would like to remind you that the vehicle is up on axle stands and you have secured it safely, in order to conform with accepted safety parameters, correct?

The steering is now on full right lock and you can see both disc pads. Now, very carefully check the position of the caliper in relation to the disc pads. Is there and equal spacing on each side? Now, have your assistant release the brake pedal and very carefully observe the travel of the disc pad pistons. They should retract and the hub should turn freely by hand. A very light drag is allowed between disc pad and disc, but it should NOT be discernible when you rotate the hub by hand.

With no pressure on the brake pedal, and using an appropriate tool, attempt to have the caliper pistons retract into their cylinders / bores. Completed? Use caution as it is very easy to break / damage a disc by using undue force when retracting the pistons.

There is now an obvious gap between disc pads and disc (or rotor..sorry) Now, carefully check that the pad guide pins are not deformed and that the pads ride easily on them. if a pad jams when the brakes are applied, then, when the piston retracts, when force is removed from the brake pedal. There is an appreciable gap to close, upon the next application of the brakes!

Some types of disc pad retaining /guide pins are a tight fit, and it is very easy to tilt a pad when fitting the pins, causing the disc pad to fail to retract fully, and again, displayed by a brake pedal with excessive travel.

When the brake pedal is applied, the brake fluid has to fill the caliper piston bores, then exert pressure on the piston to force it against the disc pads, and they in turn are forced into contact with the disc. If the piston has to move an appreciable distance before contacting the disc pad, that takes more brake fluid to fill the bore of the piston, and the master cylinder piston has to travel further,resulting in a brake pedal that displays excessive travel .

I notice that you did not mention the type of effort or number of applications of the brake pedal which resulted in a firm pedal.

If you fitted replacement calipers, can I presume that you fitted new guide pins to the calipers?
Last but not least, (a) are they the correct calipers for the vehicle as regards piston bore size? The brake Master cyl will not be able to fill the bores of the calipers with enough fluid to drive the pistons out to apply the disc pads, if the bores are oversized. The pedal will also display excessive travel.
(b) If the brake master cyl is overfilled, when the brakes are applied, the master cyl will force fluid to the calipers, expand the caliper pistons, but will be unable to release the application to the pistons due to the fluid being unable to return to the master cyl as the allotted reservoir space has been filled with static fluid. When the brake pedal is depressed again, the Master cyl cannot service the caliper pistons on the first stroke as the pistons are locked at full stroke / travel in the bores, resulting in the brake pedal going to the floor, or giving that impression.
HOWEVER, that condition, if the vehicle is driven any distance, will result in the obvious odor of overheated disc brake pads, and the vehicle struggling to display any state of acceleration.
(c) Are they in fact the correct disc brake pads? It would be wise to remove a guide / retainer pin and check for free movement of the pad on the remaining pin. All ok, then refit the pin which you removed and test again. The pads have to be free to move on the pins, and thus align themselves with the face of the disc / rotor when the brakes are applied. Some people coat the pins with never-seeze or hi-temp grease when fitting them, others prefer them to be dry.

In closing, I would recommend that you check the full travel AND RETRACTION of the caliper pistons in their respective bores. It is not unknown for re-built / new parts to be defective.

It would be interesting to hear if any of the above proved to be beneficial in resolving your problem.

Rear disc brake pads offer better performance and are not as affected by moisture like conventional brake shoe style brakes are. Rear disc brakes are similar to front disc brakes. The main difference is that rear disc brake systems must incorporate the emergency brake system. There are two methods widely used for the emergency brake with rear disc systems. The first system is a brake shoe inside the brake disc that is actuated by the emergency brake lever. The second is a screw style actuator inside the brake caliper. When activated the brake pads are forced into the brake disc and held tightly by the emergency brake lever.
READ COMPLETELY BEFORE STARTING
Step 1 - Identify Rear Disc Brake Components
Rear disc brake assembly includes; rear brake disc, rear brake pads, brake caliper mount and a caliper mounting screw. (Note: Some vehicles do not have the rotor mounting screw.)
Step 2 - Removing the Rear Brake Caliper Mount Bolts
To replace rear brake pads and rotors the rear brake caliper needs to be removed. First loosen the rear brake caliper mount bolts and remove them. Turn counter clockwise.
Step 3 - Lift Rear Brake Caliper from The Caliper Mount
After the caliper mount bolts have been removed, gently lift the brake caliper from the caliper mount. Inspect the caliper slides; they should move freely in the caliper mount. Remove rear brake pads and hardware.

Step 4 - Removing Caliper Mount Bolts
With a socket wrench or other appropriate removal tool, loosen the rear brake caliper mounting bolts. Remove bolts and lift the caliper mount and remove it from the vehicle. Remove the retaining screw from the disc mounting hole. Tap the rotor gently to release any rust that has accumulated between the rotor and bearing hub. Lift brake rotor from wheel hub holding on tightly, using both hands. You do not want to drop the rotor.

Step 5 - Removing Rear Brake Rotor
Remove the retaining screw from the disc mounting hole, tap the rotor gently to release any rust that has accumulated between the rotor and bearing hub. Lift brake rotor from wheel hub, hold on using both hands and do not drop.

Step 6 - Install New Brake Rotor
Check the new rotor against the old brake rotor to make sure they are the same size. Clean the mating surface on the wheel hub before the new brake rotor is installed. Reinstall rotor retainer screw.
Step 7 - Reset Rear Brake Caliper
Before new brake pads can be installed, the rear brake caliper must be reset. The reset tool winds the piston back into position so the new brake pads will fit. This style of brake caliper will not compress with a clamp tool; it can only be reset with the proper reset tool.
Step 8 - Reinstall Rear Caliper Mount and Install New Rear Brake Pads
After the caliper has been reset, reinstall caliper mounting bolts and make sure the bolts are tight. Then match up the old brake pads to the new brake pads. They should be exactly the same except, of course; the old ones will be worn out. Check the new brake pads for proper fit and install any brake hardware that is required.
Step 9 - Remount Rear Brake Caliper
Reinstall the brake caliper, align brake pad hardware and reinstall caliper mounting bolts. (Note: align the rear peg of the brake pad to the groove in the caliper piston.) Recheck and retighten all caliper and caliper mount bolts. Bleed brake system to relieve any air in the system. Before driving the vehicle, push the brake pedal down and let it up slowly. This operation forces the brake pads to travel to the brake rotors. DO NOT DRIVE VEHICLE until proper brake pedal operation resumes. When test driving vehicle listen for any unusual noises during the operation of the brakes.
WARNING! Always have the vehicle under inspection on level ground, in park with the emergency brake on. Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when anyone is near the battery or engine. Always have an operational fire extinguisher close by, obey all first aid instructions in the event of an injury. Never stand in front or behind a vehicle when cranked over or running. When engine is cranked over keep hands and clothing away from rotating components. Never move a car without proper brake pedal operation.

you shouldnt have to bleed anything when just doing brakes,unless you opened the bleeders and this did not have to be done, if this is what was done then bleeding is needed,close all bleeders, have someone in car, pump pedal 3 times and hold down open bleeder tell them to keep preasure on pedal as it goes down then close bleeder and then tell them to pump again and hold do this a few times on each side starting at the right rear wheel then to left rear then right front then left front always keep an eye on fluid level in master cylinder always keep it full, dont let it empty, bleed all wheels,

Try using a pressure bleeder. It will force the air out. Works every time.

hi im dave
hope i can help
when you had the rear pads applied and the discs turned was there noticeable damage to the disc surface it sounds like your e brake cable is not adjusted properly or perhaps the braided wires inside the insulation are seperating along your brake cable causing the rear brakes to not be adjsting themselves properly. Every time the parking brake is applied the rear brakes are self adjusted if they arent being applied due to slack in or a broken cable you will not adjust your rear brakes. This would accont for the flutter in the brake pedal as hydraulic fluid is still circulating to compress the pads against the rotor but the pads arent reaching the rotor.