I have replaced the vacuum booster, all wheel cylinders, the master cylinder, all rotors, all calipurs, i have replaced the rubber brake lines front and back in case they have calasped, new brakes pads, the one thing i know the two sensors in the front may be burnt, the front brakes will still get smokeing hot 10 miles down the road and this problem was there before i changed anything my next thing is to change the abs box and those two burnt sensor down by the front wheels, these are speed sensors correct?
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Check ur master cilinder , a way to know if your wheels are free, jack it up turn the wheel by hand if not realese the bleeder on top of the caliper and try again if it is free probably u need to replace master cil.
Sounds like you have an air lock in your distribution block or it could be a bad distribution block all together. Sometimes you can tap it lightly and the air lock will bleed out. Also check your vacuum booster. If it is real hard to press the brake petal down, with the motor running, the vacuum booster diaphragm is blown, or there is a vacuum leak in the line to the booster. Pull the vacuum line off the booster with the engine running to see if there is vacuum to the booster, this will likely make the engine stall out if the booster is working properly. A little trick I do when bleeding my brakes is take about 16 inches of clear tubing that fits the bleeder, then get a quart Mason jar stick the tubing that is attached to the bleeder into the jar, then add about and inch of brake fluid to the jar and start pumping the petal. Always keep an eye on the jar and your master cylinder as to not let the master cylinder run out, or the jar to overflow. Hope this helps, good luck. If I think of something else I'll do another post.
Probably there is a leak in the hydraulic brake line hoses
connecting the master and the wheel cylinder hose. Also get the brakes bleeded
to remove any air the system. also get the check valve of the brake booster
checked and the vacuum hose.
The subdued sound of a burst of air is a sign the vacuum servo or booster is functioning as it should. For most people most of the time a power booster and a vacuum booster are the same things - there are such things as various types of "power brakes" but they are in the world of specialised motoring and commercial and industrial vehicles.
I suggest you revisit each wheel brake and ensure they are all as the vehicle manufacturer intended and the front brakes are not dragging. If they are dragging when turned by hand while lifted on a jack something is clearly wrong. Try briefly releasing a fluid bleed nipple - if that improves matters the hydraulic system has residual pressure. If there is no improvement something about the brake isn't correct.
Once you have satisfied yourself everything is as it should be between the master cylinder and the ground you should ensure the brake pedal linkage is correctly adjusted and operating properly and finally before re-bleeding the hydraulics you should ensure a small clearance exists between the brake booster push rod and the master cylinder piston, about 8 to 10 thou inch is about right...
That sounds to me like a problem with the power brake booster unit or the master cylinder, the wrong master cylinder could be installed, and this could happen if the plunger rod from the vacuum booster unit is too long for the opening on the rear of the master cylinder, that is why any time that a master cylinder is replaced to be certain that the depth of the plunger valve in the rear of the master cylinder is the same as the original part that was removed. Also the brake booster itself could be malfunctioning and activating the brakes with just the engine vacuum.
Are you losing any Brake Fluid? Is it visible anywhere at the four wheels? Is it visible anywhere else?
The Master Cylinder may be defective. When you bled the Brakes did you maintain proper Brake Fluid Level in the Master Cylinder? If you didn't: and air entered into the Master Cylinder there maybe air within in the system in the Master Cylinder. You can bleed the Master Cylinder by removing the brake lines, adding more fluid, pumping the brakes, bleeding the air out of the system.
Are you losing Brake Fluid and can't find a noticeable leak? Then there is a good posibility that the rear seal in the Master Cylinder is leaking and the Fluid is going into the Brake Booster - which is the large wheel shaped drum located on the fire wall. In this case both the Brake Booster and the Master Cylinder will have to be removed and replaced. The Booster contains seals that Brake Fluid is very caustic to and will ruin these seals- causing future failures.
If no Brake Fluid is lost, no leak found: Check the Brake Booster Vacuum Advance. This should be connected to the outside of the Booster, attached to a hose, with the hose going to the engine. Check to see if this is working properly. Replace if needed.
1. What is the Brake Fluid Level?
2. Are you losing any Brake fluid at all? Are there any puddles or noticeable wetness on the ground or on the tires/wheels? With vehicle parked, the reservoir filled (overfilled), and engine running: pump the brakes and check on the ground and back sides (inside portions) of the wheels. Look for any brake fluid leaks.
3. Leaks from Calipers usually means a leak from the caliper piston. The rubber seals will be wet.
Leaks from Drums usually means a leak from the wheel cylinder.
4. In any case of leaks from the wheels - replace the calliper OR wheel cylinder.
For caliper leaks: change the brake pads, and clean the rotors with brake cleaner.
For drum leaks: clean the drum and brake hardware with brake cleaner, and replace the shoes.
5. If no leak is detected from the wheel area's: check under the Master Cylinder for wetness indicating a possible leak.
6. If no leak can be found: you MAY have a rear seal leak in the Master Cylinder which is pumping Brake Fluid into the Brake Booster (that large disk looking thing attached to the fire wall, attached to the Master Cylinder in front).
a. Use a large drip/catch pan under the Van in the area on the Master Cylinder.
b. Disconnect the brake lines from the Master Cylinder using a flair wrench.
c. Remove the two nuts (12 or 13mm?) attaching the Master Cylinder to the Brake Booster. If you have been using a lot of fluid, and have found no leaks, here is a good possibilty that all that brake fluid has collected in the Booster; so when you detach the Master Cylinder from the Brake Booster, all that fluid will come rushing out!
7. If there is Brake Fluid inside the Brake Booster: there is no cleaning that out. Brake Fluid is very caustic to the seals inside the Booster and should be replaced.
8. Of course the Master Cylinder will also have to be replaced.
9. After replacing the Master Cylinder/Brake Booster - make sure you get all that spilled brake fluid off the engine compartment area parts! I use a brake cleaner, then mild soap and then water to rinse. Clean any Brake Fluid off Paint imediatley as it will quickly dissolves finishes and paint.
10. If no leak is detected and the Booster is clear, there may be problems with the Booster One-Way Valve. This is attached to the outside of the Booster and has a hose from an "advance" connected to it. This maybe malfunctioning where you are losing power. Replace this first before deciding to replace the whole booster (in cases of NON-LEAKS ONLY). If that did not work, there may be inner seals inside the Booster that have failed. That means a new Booster.
11. In any of the above cases: Make sure you bleed the Master Cylinder correctly and bleed the brakes (at each affected wheel) correctly. Any air in the brake lines will decrease your braking proficiency or could result in brake failure.
Let me know if this helped or if you have any additional information or questions. Feel free to contact me at FixYa.com!
no they are inverted flare fittings no seals check all lines and calipers/wheel cylinders if all are dry remove the vacuum hose from the booster if there is brake fluid in the hose the master cylinder is bad