Master Cylinder - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 01-18-2007, 12:40 AM   #11
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Quote:
Originally Posted by Soulmonger
Any certain brand to get or aviod? Autozone has a remanufactured one for only $55ish it has the same lifetime warranty that the new one has and the new one is $100ish. Is it worth it to just get the reman one? or will I have more problems with it later if I do? Also is this something that has to be taken care of right this moment before I drive it again? Or will it be ok as long as it has fluid til saturday when my g/f gets paid?
How is your brake pressure? If it'* minimal or non-existant I'd change it asap, but if you don't have money you either don't drive it or be very careful. When mine went I drove for 1 1/2 weeks (700 miles) with no brake pressure. I was lucky, but I was also extremely cautious driving. I wouldn't recommend it though.

EDIT: Also, where exactly is the fluid leaking out of the MC? If your MC was SHOT, you shouldn't have significant, if any, brake pressure. I don't think you mentioned anything about your brake pressure decreasing.
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Old 01-18-2007, 11:53 AM   #12
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Brakes are a bad choice for deferred maintenance. And brakes are something you want to make sure you do correctly. Park it until you fix it. It is not likely that you will be able to change the master cylinder without introducing some air into the brake lines that connect to it. This means that you need to bleed the brakes after the new MC is installed. The work is not difficult, it just takes a few hours to get it done. You will need a jack and support stands (preferably 4) to support the car, some Power Blaster penetrating oil for the bleeder screws, 10mm and 8mm box wrenches for the bleeder screws, a quart of brake fluid, a couple of feet of small bore rubber or vinyl hose, a catch pan and a helper who can press the pedal down and not release it until you have opened and closed the bleeder. Here are some instructions for you:
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Originally Posted by bill buttermore
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 interuppted 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.

Good luck!
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Old 01-18-2007, 11:37 PM   #13
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There is no noticeable pressure loss. The breaks work as well as they always have. I will be replacing the MC tomorrow instead of saturday however.
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Old 01-19-2007, 09:22 AM   #14
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Quote:
Originally Posted by Hans
99% its the MC...its a somewhat common failure on your year...common every 100,000 or so. Mine has been replaced for the exact same problem.
For future searches etc. I'd like to mention that this information is not accurate. Many on the club never experience a failure up to 200,000 or further, others have one much sooner than 100,000. A master cylinder is like a water pump.. you can have a failure at any time or it can go to the junkyard when the car finally dies.
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Old 01-19-2007, 02:00 PM   #15
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Quote:
Originally Posted by jams04
Yep mine was leaking right there at the brake booster. Took about 45 minutes to bleed the new MC and install it. I didnt have to bleed the brakes. Is that normal, did mine about a week ago.
Same with me i never had to bleed the brakes, as long as you get all the air out of the new M.C. and dont shake and flud out of the lines, when working on it,
but if the MC got too bad and sucked up air then thats a given
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Old 01-19-2007, 02:10 PM   #16
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When I have replaced Master cylinders I have blead at the master cylinder just to make sure..

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Old 01-19-2007, 02:12 PM   #17
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I also bled to make sure.

Afterall.. you are introducing air into the lines right where they hook to the master cylinder.
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Old 01-19-2007, 02:28 PM   #18
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I agree... Easy to do and only takes a couple of minutes...

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