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I change master cylinder brakes and still getting air in the brakes i have bleed brakes twice and the problem still there, gets better for about 3 days afeter that the problem persist
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When you say that the first master cylinder had no pedal, did that just suddenly happen?
A master cylinder has rubber seals inside - think of a bicycle pump - when the bicycle pump seal wears it becomes difficult to pressurise it. The same is true of a master cylinder.
A classic sign of a master cylinder with worn or perished seals is that it needs pumping a few times to pressurise but there is no leakage of brake fluid.
Prior to you changing the master cylinder had the level of the brake fluid dropped .. indicating a leak somewhere? Had you done any work on the brake pads/rotors?
Eliminate other causes of air getting into the braking system:
First thing to do is check the flexible brake hoses on each wheel. Get a friend to pump - and hold - the brake pedal while you inspect the flexible hoses. Check for leaks (obviously) but also look to see if each flexible hose 'bulges' anywhere along its length.
Also check each flexible hose to see if it is perished or wet with fluid.
A perished flexible hose can draw in air and cause no pedal/spongy pedal. The same is true with a flexible hose that bulges/balloons when under pressure.
It only takes a slight 'weeping' from a flexi hose or rigid pipe connection to allow air into the system. Check the rigid brake pipes too - especially where there is a connector/join.
Then remove the road wheels and look for the slightest fluid leak around caliper pistons.
The problem, I think, comes back to the original fault .. no pedal when your car had sat overnight. This is rather indicative of air getting into the system somewhere though not necessarily from the master cylinder.
Check for the slightest leak in the entire braking system. It only takes a small amount of air to get in and cause problems. The fact that you fitted a second master cylinder makes me think the problem could lie elsewhere.
Try bleeding the braking system. It's a 2 man job, but quite easy.
Here's a link that explains how to do it: How to Bleed Your Brakes
The master cylinder is mounted on power brake unit (the big black round canister) on firewall held down with 2 12mm nuts depending on braking system usually 2 10mm brake lines need to be removed on out it comes. Bench bleed new master cylinder before install . Fill reservoir with brake fluid and slowly push piston about 1 inch back and fore until air is gone ( assuming mater comes with bench bleed kit ) then install and repeat with someone pressing on pedal lock line closed before pedal is released again EG pump pedal ok hold it (open line watch fluid come out close) ok let up pump it up again repeat may be twice per line. the pedal should be firm once done.
Hi there: I suggest to check this procedure, when the hydraulic brake system must be bled whenever a fluid line
has been disconnected because air gets into the system.
A leak in the
system may sometimes be indicated by a spongy brake pedal. Air trapped
in the system is compressible and does not permit the pressure applied
to the brake pedal to be transmitted solidly through the brakes. The
system must be absolutely free from air at all times. If the master
cylinder has been overhauled or a new cylinder has been installed, bleed
the cylinder on a bench before installation. When bleeding brakes,
bleed at the wheel most distant from the master cylinder first, the next
most distant second, and so on. During the bleeding operation the
master cylinder must be kept at least
3
/
4
full of brake fluid.
The ABS bleeding procedure is different from the conventional method. It consists of the following three steps: Step 1: Conventional manual brake bleed. Step 2: Bleeding the system using the DRB scan tool. Step 3: An additional conventional manual brake bleed.
The recommended ABS bleeding procedure is as follows:
To bleed the brakes, first carefully clean all dirt from around
the master cylinder filler cap. Remove the filler cap and fill the
master cylinder with DOT 3 brake fluid to the lower edge of the filler
neck.
Bleed the master cylinder first. Have a helper operate the brake
pedal while bleeding each master cylinder fluid outlet line. Do not
allow the master cylinder to to run out of fluid,as this will allow
additional air to be drawn into the cylinder.
Bleed the brake system in the following sequence:
Master cylinder
HCU valve body (at fluid lines)
Right rear wheel
Left rear wheel
Right front wheel
Left front wheel
Clean off the bleeder connections at all four wheel cylinders.
Attach the bleeder hose to the right rear wheel cylinder bleeder screw
and place the end of the tube in a glass jar, submerged in brake fluid.
Open the bleeder valve 1/2 - 3/4
of a turn.
Have an assistant depress the brake pedal slowly and allow it to
return. Continue this pumping action to force any air out of the system.
When bubbles cease to appear at the end of the bleeder hose, close the
bleeder valve and remove the hose.
Check the level of fluid in the master cylinder reservoir and replenish as necessary.
After the bleeding operation at each wheel cylinder has been
completed, fill the master cylinder reservoir and replace the filler
plug.
Do not reuse the fluid which has been removed from the lines through
the bleeding process because it contains air bubbles and dirt.
Perform the "Bleed Brake'' procedure with the DRB II scan tool.
This procedure is described in the DRB II software information and
diagnostic guide.
Attach the DRB II scan tool to the diagnostic connector.
Run the Bleed Brake procedure as described in the DRB II tester guide.
Repeat the conventional bleeding procedure as previously outlined.
Fill the master cylinder reservoir to the proper level.
you must have a lot of air in system. the brakes need bleed to let the air out of system. did you bench bleed the master cylinder before putting it on car ! if not thats why no brakes. to bench bleed a new master cylinder, put it in a vise. fill it full or the proper level of brake fluid. push on the plunger with a dowel or another object. pump it till all air is out of master cylinder, you can tell when no air. it will be all fluid coming out of cylinder. keep checking brake fluid in master cylinder.make sure you push plunger in all the way.when all air is gone replace on car. if you do not loose any fluid from the master cylinder lines, then you can replace it without having air in system. bleed each wheel if needed. good-day!
Well, if you change a caliper or a brake line the fluid in the master cylinder should remain, even if the fluid leaks out.
However, if you are having trouble bleeding regularly, then use a vacuum pump with a 'can' or use a pressure bleeder (I prefer this method) that costs about $55 or so available on the Internet.
If you use a pressure bleeder, you'll need an extra master cylinder cap that has a hole drilled in it to accomodate the fittings of the pressure bleeder.
I know someone who had a Lincoln Continental that changed a brake line and had trouble bleeding it, and they used a vacuum pump and it bled easily using that method.
Some cars require that when you change the master cylinder, a brake scan tool is required to bleed the master cylinder that has air in it. But, if you did not replace the master cylinder, you should be able to use either the vacuum or pressure method to bleed the brakes easily.
You changed the master cylinder and vacuum booster and have no leaks anywhere, but did you bleed the entire brake system after you did this work? A little bit of air in any of the lines will make the brakes ineffective.
Did you bleed the master cylinder before you put it in the vehicle?This usually makes it easier to bleed the entire brake system if this is done before you install the master cylinder.Other wise all you have done is put air in the brake system.The master cylinder kit usually comes with a bleeder kit.This is for bench bleeding the master.Hope this helps.Good luck.
You bleed it like you would a normal system but you must use the boost assist to do it, in order to do this start the truck pump the brakes three times and bleed that cylinder farthest away from the master cylinder do this twice or until you get clear fluid to run out. add fluid for every cylinder before moving on. Do this for each wheel and after doing all four wheels you should be ready to go. If it feels mushy you will have to bleed it a second time. But you must have the engine running to bleed the brakes unless you have a power bleeder. You may want to bleed the master cylinder first to do this add fluid to the cylinder then pump brakes three times crack the front line open and allow it to bleed air rout of the line do the same for the rear master cylinder once yo get solid fluid from the master cylinder you can dot the same for the ABS then do the wheel cylinders and wheel calipers. This needs to be done sometimes, be sure to never let the master cylinder run out of fluid and check it each time you bleed the wheel cylinders.
The master cylinder supplies the pressure to the brake fluid that travels between the maste brake cylinder resevoir and the brake caliper pistons (through the brake lines. If the master cylinder fails there will be insufficient compression of the brake fluid to make the calipers operate as designed. Leaks in the brake lines and/or cylinders is a possibility, and unrelated to functionality of the master cylinder. Also, pistons located in the brake calipers can form a corrosion ring on their inside walls if there is breakdown in the brake fluid or moisture that gets into the lines. Operating the vehicle when there is insufficient brake fluid in the master cylinder resevoir can also lead to air getting into the brake lines, causing bad working brakes. Air compresses more than brake fluid, and the master cylinder isn't designed to compress air in the brake lines. Sounds like a bad case of "lack of maintenance", as opposed to bad advice from the mechanics. That said, there's no excuse for bad installation. But, it's tough to improperly install a brake line since they are nothing more than hollow metal tubes. There should be no rubber connectors installed in the brake lines. When bleeding the brake lines one must remove all of the trapped air before you will see any fluid appear. If the valves in the master cylinder are not properly operating the master cylinder will not allow the brake fluid to get into the brake lines.
Also check each flexible hose to see if it is perished or wet with fluid.
A perished flexible hose can draw in air and cause no pedal/spongy pedal. The same is true with a flexible hose that bulges/balloons when under pressure.
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