Brake pedal to the floor - no brake pressure - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-09-2008, 09:45 AM   #1
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Default Brake pedal to the floor - no brake pressure

I replaced the front right brake hose and attempted to bleed the brakes. I had my friend pump the brakes and then hold the pedal down - then I opened the bleeder. No hiss or fluid came out. Tried a few more times - same result - but now the pedal goes to the floor - no pressure at all. I checked the other front bleeder - same issue no hiss no fluid. I loosed the two brake lines at the master cylinder and had my friend pump the brakes - no hiss no fluid - the brake reservor is full. Shouldn't fluid squirt out?

I had replaced the master brake cylinder a few weeks ago and bench bleed the master cylinder per instructions with the unit. The only odd item I noted is a rubber hose attaches to the reservoir and goes to the ABS unit. I had to cap the reservoir hose connection so the brake fluid would not leak out of the reservoir. I attached the master cylinder to the power booster and filled the hose with brake fluid and reattached it to the reservoir. I bleed the brakes without issue. The brakes have worked fine since the MC replacement.

Do you guys think the master cylinder has gone bad - it was new not a rebuild? Do I need to bench bleed it again? Did I bleed it incorrectly. Should I of filled that hose leading to the ABS unit from the reservior with fluid? The hose was full when I disconnectd it. Please advise.

Thanks.....Bob
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Old 05-09-2008, 10:02 AM   #2
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You always bleed the furthest to the closest and in that order, no short cuts.
Passenger side rear
driver side rear
passenger side
driver side
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Old 05-09-2008, 11:15 AM   #3
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Should I bench bleed the M/C again and then bleed brakes in the order noted?
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Old 05-09-2008, 11:31 AM   #4
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I'm don't understand why brake fluid does not squirt out of the M/C ports when the pedal is pumped. Don't know if the M/C is bad or another bench bleed is needed.
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Old 05-09-2008, 11:32 AM   #5
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I'd try the bench bleed again, fluid should have come out when you loosened the lines at the master cylinder. If the bench bleed fails then return the master cylinder.
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Old 05-10-2008, 09:56 AM   #6
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As others have suggested, you either have a bad master cylinder or you allowed air to be sucked into the system when you attempted to bleed the brake lines. Air is sucked into the system when an opening to the atmosphere is present and the brake pedal is released. This can happen when a fitting is loose or a line is broken or rusted through anywhere in the system. Air can enter if the MC reservoir is allowed to empty. It can also enter if the brake pedal was released at any time that you had not closed a bleeder valve or re-tightened the fittings you had loosened at the MC.

If you use the search feature at the top of the page with "bleeding brakes" as the topic, you will find these instructions:

Quote:
Originally Posted by bill buttermore
You need to flush fluid at each bleeder until air comes out, and then no air comes out. For all four wheels, this will typically take more than one refill of the master cylinder reservoir. If you only bled enough that you did not see an appreciable drop in the reservoir, you did not move the air to and out of the bleeders. Each opening of the RR bleeder screw will discharge maybe a foot or so of fluid within the line. You are a good ten feet away, so figure ten or so openings of the RR bleeder screw. Check the MC reservoir after several bleeds to make sure you are not getting too low. If you let the reservoir empty, you will introduce air into the system necessitating bleeding the MC again, as well as the lines.

Here is a bleeding procedure writeup for the master cylinder by willwren:

Quote:
Originally Posted by willwren
The kit will come with two new pins to hold the reservior to the MC, as well as two green fittings to screw into the MC, and two clear hoses. The instructions are mostly good.

Put the MC in a vise (upright) with the vice jaws on the bottom of the mounting flange, with the flange facing you so you can push on the piston (simulate the brake pedal). Install the green fittings and tubes. Fill the res (you must plug the outlet for the PMV reservior fill). Go about half full on the MC, but you may have to tip/tilt it to get the fluid to the front chamber also.

Put it back in the vice with the piston/flange facing you, and run both hoses into a small container of brake fluid, with the ends being under the surface (fully immersed).

Push the piston all the way in, hold for a couple seconds, and release. Wait for the bubbles in your little container to dissipate so you don't suck them back in on the next cycle. Repeat this process several times until there'* no more air. At that point, you can lift the tubes out, but leave them on. They'll keep it from leaking (make sure you hold them up so they're higher than the reservior as you install the MC). Bolt the MC on to the booster, then pull your plug underneath quickly, and hook up the 3/4" feeder to the PMV reservior, then remove the green fitting and tube closest to the firewall, and re-connect that brake line (rear first, it'* easier). Then do the same for the forward fitting.

Bleed the entire system.
And here is a bleeding procedure I wrote up for the service brakes:

Quote:
Originally Posted by bill buttermore
Just to review the procedure, here is how I do them

OK, The idea is to remove any air bubbles in the brake lines from the master cylinder to each wheel cylinder (rear wheels) or caliper (front wheels).

These directions presume you have a good master cylinder or a new one that has been bench-bled.

You will probably need to remove the rear wheels to gain access to the wheel cylinder bleeders. You may be able to get at the front bleeders on the calipers by turning the wheels all the way left or right. I find bleeding is a lot easier with all the road wheels removed and the car up on stands. Never get under a car supported only by a jack!

Start by filling the master cylinder reservoir and replacing the cap. Don't let brake fluid be exposed to the air - it will absorb moisture from the atmosphere which can cause troubles in the brake lines. What you want is to have a helper pump the pedal a couple of times (press down - release; press down - release) then press down and hold. While he is maintaining pressure on the pedal, you open the bleeder valve on the wheel cylinder or caliper and relieve the pressure by releasing fluid from the bleeder valve. The brake pedal will suddenly go down, at first nearly all the way to the floor. The helper must not allow the pedal to come up while the bleeder valve is open or air will be sucked in through the bleeder valve. At the wheel, when the fluid flow stops, close the bleeder screw and instruct your helper to release the pedal, then "pump and hold" again. After a few times, depending on how much air is in the lines and where the air is located, you will notice as you open the bleeder valve, that the fluid flow is interrupted by escaping air. It kind of makes a "spitting" sound. That is good - that'* the air you are trying to remove. Keep repeating the procedure until the stream of fluid is solid - no air - and clean in appearance.

While you are bleeding each wheel, after about five or six squirts, check the level of fluid in the master cylinder reservoir. If you let the reservoir go empty, you will introduce air into the lines and you will have to bleed the master cylinder and all the brakes again.

I like to place a box wrench on the bleeder screw nut in a position that allows me to both open and close the valve (hopefully) without repositioning the wrench. I then attach a length of flexible vinyl tubing (maybe 3/16" inside diameter) that fits tightly over the end of the nipple on the end of the bleeder. I run the hose into a plastic pan to catch the fluid that comes out. Be careful, brake fluid removes paint. Also, don't use more than a couple of foot-pounds of torque to close these little bleeder screws - they are not solid and they can break off very easily.

There are a couple of inexpensive one-man methods. You can use a vacuum pump to suck out the air from each line, but the problem with that is that you have to open the bleeder screw to open the line and when you do, you usually end up sucking some air through the threads on the bleeder screw making it difficult to know when you have all the air out. An older method is to take the hose described above and put it into a (clean and dry) coke bottle with the end of the hose submerged under a couple of inches of brake fluid. This is not a bad idea, even with a helper, cause if your helper screws up and releases the pedal when the valve is still open, it will suck mostly fluid in from the bottle instead of air. The problem with this method is the same as with the vacuum pump. That is, on the release stroke, if the valve is open, air can be sucked into the system through the threads on the bleeder screw.

Be careful if your bleeder screws are corroded. They will break off in the cylinder or the caliper with surprisingly little force applied, and then you have a real piece of work on your hands. A good plan is to squirt around the bleeder screw (not into it) with a good penetrating oil like power blaster, kroil, or sea foam deep creep (WD-40 is not very good for this). Remove the cap from the screw and give it a couple of taps square on the end of the screw with a small ball-pein hammer, and squirt again to encourage the oil to penetrate the threads. Best if you can let it sit overnight, but give the oil at least 30 minutes to work before you try to open the bleeders.

If your bleeders don't have the little rubber caps on them, make sure the passage is clear to let the fluid out. Sometimes you have to clean them out with a small drill bit.

The traditional method is to start at the wheel farthest from the master cylinder, usually the right rear, and work to the shortest run, i.e., the left front. As you work your way around, the pedal should become firmer and progressively higher from the floor. When you are done, if you have removed all the air, the pedal should be firm, there should be no "sponginess," or softness when depressed.

I would not touch the ABS system other than to very carefully clean, remove, and plug the top end of the hose that runs down to the ABS pump reservoir when you change out the master cylinder. It is very important that you do not introduce any dirt into any part of your brake system.


Here is what the FSM says:

According to the factory service manual for the '92 Bonneville with ABS, the bleeding procedure is pretty much as above EXCEPT they instruct that before you start to bleed the brakes, you deplete the vacuum in the booster by applying the brakes a few times with the engine off. (This is the power brake booster vacuum can behind the master cylinder, NOT the ABS pump.) They also instruct that the helper press slowly down on the pedal and hold only once for each time the bleeder valve is opened. Then the pedal is released and you wait 15 seconds before pressing down only once again. This is done with the ignition and engine off.
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Old 05-10-2008, 11:11 AM   #7
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Default master

Bench bleed the master again, then bleed the lines attached to the master, then the wheels.
Had this happen on my mom'* Park Ave once, the wheels would not bleed until I went back to the master and bled the lines attached to it first.
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Old 05-12-2008, 10:13 AM   #8
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I pulled off the 3 week old M/C and found the piston was fully depressed in the bore and seized in place - I attempted to push it in and taped the M/C with a hammer but the piston did not release. I took it back to the parts store and swapped it under warranty for another remanufactured one. I bench bleed it and bleed all four brakes. I test drove the car around town. Brakes work nice with no dragging from the front right brake caliper (I had previously replaced the brake hose and upon attempting to bleed the brake the peddle sank to the floor) This Wednesday I'll be driving the car to work on a highway - I'll see how the brakes work then.

Thanks guys for all your advise. I'll post, hopefully, a brake repair success post this Wednesday after work.

Next project - clean out the evaporator fins to obtain decent air volume out of my interior heater/cooling air ducts

Thanks -- Milty
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