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Old 03-21-2008, 10:01 AM   #1
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Default Brake bleeding

Ive ran into a few problems when i replaced my master cylinder. The install went smooth. no leaks, great pressure and bleed the system. As soon as i start the car up the breaks become soft again and go right to the floor. Ive bleed the system twice and im kinda lost in what the problem is. I think im gunna bring it to a shop this afternoon when i get off work and just have them bleed it. Just curious if any one knows whats wrong or how to fix it.
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Old 03-21-2008, 10:09 AM   #2
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You need to FULLY bleed the system starting at the farthest point (right rear), then left rear, then right front, then left front.

Until the system is completely purged. All fluid replaced. You opened the system at the farthest upstream point possible. This dictates fully bleeding. When you say you've bled twice, was that a couple pedal pumps, or several? Was it enough to fully purge? During your bleeding, how often did you have to refill the MC reservior?
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Old 03-21-2008, 12:59 PM   #3
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Have you considered a Motive Products one-man pressure bleeder?:
http://www.motiveproducts.com/02bleeders.html

I can personally vouch for the effectiveness of this tool in doing a bang-up job of completely replacing the fluid in your braking system and getting rid of all air.

This thing makes the job so easy, brake fluid replacement will become a routine yearly maintenance item for you.
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Old 03-21-2008, 03:20 PM   #4
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Yea i started with the right rear, then the left rear, up to the front right then to the front left. What i mean by bleed it twice is i did a full cycle bleed and it wan'ts sufficent so i did it again. I did several pumps and held the pedal and opened the bleeder valve. Fluid came out and the pedal went to the floor. I closed the bleeder valve and released the brake pedal. Repeated the process again and moved on to the next wheel. When i finished all four wheels the pedal was solid but when i started the car and apllied the pedal it went down to the floor. As for refilling the MC reservoir dont remember having to because the fluid level didnt seem to go down much, could i not be bleeding each wheel enough? I think the problem lies where im bleeding the brakes from. On the drum brakes there is a bleeder screw on the back right below a some kind of grease piston. theres not enough room tho get the flare nut wrench so i bleed at the other end of the steel line...ill post some pics when i get a chance if you can picture what im talking about.
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Old 03-21-2008, 03:31 PM   #5
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Default bleed

You should bleed the lines on top at the master first, then proceed to the wheels. 3 pumps then hold, bleed.
If it still goes to the floor you may have a defective master.
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Old 03-21-2008, 04:47 PM   #6
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I did bench bleed the master but i guy i work with did say it could be a faulty master. Im gunna be pissed if it is...good thing its under warranty tho.
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Old 03-21-2008, 05:06 PM   #7
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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 03-21-2008, 07:18 PM   #8
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I don't want to sidetrack you from getting the bleed done properly. But before you give up and take it to the shop and pay, don't laugh, hear me out ... check to see if either of your wheel cylinders are leaking.

I was pulling my hair out, trying to bleed mine and could never get a good pedal. So I paid and took it to my trusted brake man explaining my situation (he had replaced the MC some months before).

Since all the logical things were tried, he found one wheel cylinder with a small leak. He had seen this on a couple of others and replaced it, fixing my air problem. He said he theorizes that after braking, when the cylinder retracts back in, it sucks air in at the leaking seal.
You can shake your head; I did; but it fixed my problem.
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Old 03-21-2008, 07:45 PM   #9
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Cliff'* notes:

Properly bench bleed master cylinder.

Bleed all 4 wheels completely, Right Rear, Left Rear, Right Front and Left Front. This is starting from the longest line and going in order to the shortest line. This is necessary so that you do not reintroduce air back into the master cylinder bore. One of the cheapest and best ways of doing this yourself is to take a glass jar, put a good amount of brake fluid in it...and then get a proper length of clear flexible plastic tubing. 1/8" ID should do it, IIRC. Something that makes a very snug connection over the bleeder valve. Then put the end of the tube in the jar with the brake fluid, open the bleeder valve and then pump it a few times. You can either do it yourself, or with someone else, I prefer someone else so you can witness the amount of air actually coming out of the line. Make sure to fully tighten the bleeder before removing the submerged tube.

Always make sure to constantly check the master cylinder'* fluid reservoir every time you change wheels. If it empties, and ANY air gets back into the bore, you've got to remove the master cylinder, bench bleed it again, and start the entire process over again.

A few side notes:
if your vehicle has over 100k miles, it is advised that you change both of the wheel cylinders when changing the master cylinder. They operate on just about the same premise, and wear out just the same. They're very cheap, and VERY easy to replace.

You will NOT get a firm pedal unless all parts of your brake system are up to proper operating spec. This includes all 4 brake hoses (they collapse internally, allowing fluid past the inner layers, leading to no fluid returning to the master cylinder, and eventually a big hole in the line), the front calipers (the pistons do end up leaking over time), rear wheel cylinders, master cylinder and possible rusted brake lines (this is normally only possible in salt states, for vehicles driven in it), as a guideline, its a good idea to replace these items every 100k. A very small investment to safety.
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Old 03-23-2008, 12:41 AM   #10
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Well good news, i did get the car bleed and have some what good brakes. I feel a little air so im thinking the master didnt bench bleed that well. Theres no leaks and i got the car up to about 40mph and it stopped pretty good. I went out and got a brake bleeding kit and it made all the difference. Thanks for all the input, helped out greatly.
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