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I have a 1986 F250 with a 6.9l diesel engine that I recently replaced the master cylinder and the power booster on. Now I have no brake lights I have tested the brake light switch for incoming voltage and it is good. I tested the switch itself and it is good because it mis infinite when it is open and nearly zero when the contacts are closed. Their is continuity at the brake lights themselves and the bulbs are good as well. I am not sure what else could be wrong.

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Check the brake light switch adjustment. With the new master cylinder and booster the distance you push the brake pedal down may have changed and not be far enough. Test for power going out of the switch when you press pedal with your hand, if you get none readjust the switch by moving it away from the point where the pedal hits it. You should be able to push hard enough with your hand to make the brakelights come on if the engine is running.

Posted on May 14, 2010

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How to tell is the brake booster is bad in a 1986 dodge D100


This is a standard Vacuum operated brake booster.. If you are having fluid leaking at the rod that attaches the brake pedal to the booster it is a bad Master Cylinder. The Brake fluid will eventually destroy the diaphram in the booster if it hasn't already. . Replace or rebuild the Master Cylinder and wash the brake fluid out of the booster. When the booster goes bad the brake pedal will become very hard to push.. because you will have lost "boost" This is not really a hard job. If fluid id leaking somewhere else.it should be very easy to spot.. Brake fluid looks like oil leaking..

May 13, 2014 | 2005 Cadillac STS

1 Answer

Step by step instructions for replacing brake booster on a 1999 Toyota Camry


its my pleasure to answer your question how to replace the brake booster :
1 With the engine off, step on the brake pedal several times to relieve the brake booster of vacuum.
2 Press the brake pedal down and start the engine. Verify that the brake pedal sinks slightly. Turn off engine.
3 Remove the vacuum hose from the brake booster.
4 Remove the brake lines from the master cylinder. Remove the master cylinder from the brake booster. Plug the fittings to prevent brake fluid seepage.
5 Disconnect the brake pedal from the push rod.
6 Have an assistant hold the brake booster from inside the engine compartment. Remove the nuts that hold the brake booster to the firewall. These nuts are usually located under the dash on the interior of the firewall.
7 Remove the brake booster.
8 Install the new brake booster to the firewall. Tighten the mounting nuts.
9 Connect the push rod to the brake pedal.
10 Connect the vacuum hose to the brake booster.
11 Attach the master cylinder to the new brake booster and reconnect the brake lines.
.12 Bleed the brakes at the master cylinder.

Oct 04, 2013 | Cars & Trucks

1 Answer

Replace brake booster


here you go...

The power brake booster is a tandem vacuum suspended unit. Some models may be equipped with a single or dual function vacuum switch which activates a brake warning light should low booster vacuum be present. Under normal operation, vacuum is present on both sides of the diaphragms. When the brakes are applied, atmospheric air is admitted to one side of the diaphragms to provide power assistance.
REMOVAL & INSTALLATION

1994-97 Models
See Figures 1 and 2
  1. Apply the parking brake and block the drive wheels.
  2. Remove the master cylinder-to-power brake booster nuts, then reposition the master cylinder and combination valve out of the way; if necessary, support the master cylinder on a wire to prevent damaging the brake lines.

When removing the master cylinder from the power brake booster, it is not necessary to disconnect the hydraulic lines, therefore the brake system should not have to be bled.
  1. Disconnect the vacuum hose from the power brake booster.


12_11_2011_8_48_59_pm.gif

Fig. Fig 1: Common power brake booster attachment


  1. From under the dash, remove the retainer and washer from the brake pedal on 1994 utility models. On all other models, remove the retainer and brake switch from the brake pedal.
  2. Disconnect the pushrod from the brake pedal.
  3. From under the dash, remove the power brake booster-to-cowl retaining nuts.
  4. Back under the hood, remove the power brake booster and the gasket from the cowl.

To install:
  1. Position the booster to the cowl using a new gasket.
  2. Install the bo oster retaining nuts and tighten to 16 ft. lbs. (22 Nm) 1994 utility models, 24 ft. lbs. (32 Nm) on 1994 pick-up models and 27 ft. lbs. (36 Nm) on all 1995-97 models.
  3. Connect the pedal pushrod and install the washer or switch and the retainer.
  4. Connect the vacuum hose.
12_11_2011_8_52_07_pm.gif

Fig. Fig. 2: Checking the piston booster rod using the gauge tool

  1. For all vehicles cover ed in this guide, gauge the booster rod:
    1. Apply 25 in. Hg (85 kPa) of vacuum using a hand held vacuum pump or apply maximum engine vacuum.
    2. Chec k the maximum and minimum rod lengths using J-37839 or an equivalent pushrod height gauge.
    3. If the piston is not within limits, install a service adjustable piston rod and adjust it to the correct length.
  2. Reposition the master cylinder and combination valve bracket to the booster studs, then secure using the retaining nuts. For details, please refer to the master cylinder procedure located earlier in this section.
  3. Start and run the engine, then check for proper booster operation.

Dec 11, 2011 | 1996 GMC Jimmy

1 Answer

1986 5.0 brake problems...replaced brake booster twice and master cylinder once....now there is no power to the brakes...the brakes are stiff while the care is off....but when the car is on the brake pedal...


Did you check and adjust the push rod that comes out of the booster, and in turn pushes the rod in the master cylinder??
If its too long, the piston in the master cylinder won't move back far enough to pull brake fluid in.
If it's too short, it won't contact the piston at all.

It doesn't move as much as you might think.
If instructions came with the new booster, they may address this, and how to adjust it.

Aug 29, 2011 | 1986 Ford Mustang

2 Answers

I have a hard brake peddel almoust have to stand on them what could this be


You no longer have vacuum assistence. The brake master cylinder is mounted on the brake booster which uses vacuum generated by the engine to "help" you push the brake pedal. On diesel engines there is normally a vacuum pump on the rear of the alternator which generates this vacuum. On petrol engines the vacuum is generated by the engine itself. Follow the pipe from the booster to the inlet manifold or alternator(diesel) and check for leaks along the whole length and at the joints. Replace the pipe if leaking. If no leaks are found the booster needs replacing. If you have a diesel engine, check the operation of the vacuum pump first before replacing the booster. Make sure the alternator is turning(belt in place) at idle. Disconnect the pipe at the rear of the alternator and hold a piece of paper over the pump opening to check operation. Do not use your hand as this will result in injury even with the engine at idle. Replacing the booster will see you upside down under the dashboard swearing, pleading and begging because that's where the bolts are that hold the booster in place. The master cylinder needs to be removed from the booster before the booster can be pulled from the engine bay.

Oct 20, 2010 | 1991 Chrysler Town & Country

5 Answers

Brake pedal is hard but brakes not very effective. booster holds vacuum. replaced booster check valve, no change. dash brake light stays on most of time but sometimes goes out for a while then comes back...


Check the brake fluid first.is it low or no brake fluid at all.is the brake fluid got dried up or leaked out. Sounds like the power brake booster is bad, that is what the master cylinder is bolted too. There is a rubber hose that has a plastic valve in it were it snaps into the booster, Pull that rubber hose out of the booster and off of the engine, Now the end that you took off the engine. You should be able to **** through the line, but not be able to blow through it. If you can then replace the valve, It is a one way valve.
If that is all right then hook hose back up to the engine and start engine, You should hear a major vacuum leak at the valve end, put you finger over the valve and it should stop making noise and engine should smooth out. If it don't the rubber hose must be leaking or the tube on the engine were the hose hooks to is stoped up.
Also check the master cylinder if power booster is replaced. If the brake light is coming and going check the brake light switch. check fig for the internal assembly parts:-- bdea807.gif

To check engine vacuum, connect a vacuum gauge to the supply hose that runs from the intake manifold to the booster. A low reading (below 16 inches) may indicate a hose leak or obstruction, a blockage in the exhaust system (plugged catalytic converter, crushed pipe, bad muffler, etc.), or a problem in the engine itself (manifold vacuum leak, bad valve, head gasket, etc.).
The condition of the diaphragm inside the booster is also important. If cracked, ruptured or leaking, it won't hold vacuum and can't provide much power assist. Leaks in the master cylinder can allow brake fluid to be siphoned into the booster, accelerating the demise of the diaphragm. So if there's brake fluid inside the vacuum hose, it's a good indication the master cylinder is leaking and needs to be rebuilt or replaced. Wetness around the back of the master cylinder would be another clue to this kind of problem.
To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced.
Vacuum boosters also have an external one-way check valve at the hose inlet that closes when the engine is either shut off or stalls. This traps vacuum inside the booster so it can still provide one or two power assisted stops until the engine is restarted. The valve also helps maintain vacuum when intake vacuum is low (when the engine is under load or is running at wide open throttle). You can check the valve by removing it and trying to blow through it from both sides. It should pass air from the rear but not from the front.
Replacing a vacuum booster is a fairly straight forward job. All you have to do is disconnect it from the brake pedal on the inside and unbolt the master cylinder. The pushrod that runs from the booster into the back of the master cylinder must have the specified amount of play.
You will typically find the power brake booster mounted on the firewall attached to the master cylinder. The master cylinder is connected to the brake pedal.
Thanks. keep updated for any more query.you can rate this solution and show your appreciation.

Jul 15, 2010 | 1997 Ford F250 SuperCab

1 Answer

1986 blazer power brake booster leaking on firewall inside the cab???


you should replace the booster and master cylinder. With brake fluid there ,the diaphram in the booster will be damaged .

Apr 23, 2010 | 1986 Chevrolet S-10 Blazer

2 Answers

I have very little rear brakes on my 91 w350. the shoes are fine and so are the wheel cylinders. I have recently replaced the master cylinder and had the system power bled at a shop. Is it the...


I assume you bled the rest of the system. If so check your rear adjustment. Adjust the parking brake at the same time. If no fix, then open up your rear brakes and inspect the hardware, cylinder/caliper, and adjuster. Only after all that would I suspect the proportioning valve. Ways to test that vary vehicle to vehicle. Good luck!

Apr 20, 2010 | Dodge W250 Cars & Trucks

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