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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 12-27-2006, 09:41 PM   #1
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Default Master Cylinder

How hard is it to change the master cylinder? Somthing that i could accomplish myself with minimal tools? What are the steps? On my 92. Thanks for the help...
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Old 12-27-2006, 10:25 PM   #2
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You need a couple of flare wrenches (line wrenches) the right size for the line nuts that attach to the MC. And whatever wrench (13mm?) for the two bolts that hold the master cylinder on to the booster. If your replacement MC does not include the reservoir, you will need a pin punch or equivalent to drive out the pin that holds the nylon reservoir onto the cast MC body. Clean out the old reservoir if you will be reusing it finishing by flushing it with clean brake fluid. Follow the directions for bench bleeding the master cylinder that come with the new or rebuilt unit. Install the cylinder on the two bolts, then start the line nuts by hand before you touch them with a wrench. Refill the reservoir and bleed the brakes. Clean up any brake fluid spills and keep it off the paint. Brake fluid will remove paint.
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Old 12-27-2006, 11:26 PM   #3
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It'* cake..

Having never done one before the Fake Canadian'*... it was probably a 30 min job w/o knowing what we were getting into and reading instructions
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Old 12-29-2006, 02:40 AM   #4
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can i do it myself or do i need someone to help bleed it?
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Old 12-29-2006, 03:07 AM   #5
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It always helps to have someone pump the brake pedal while you bleed the brakes.
You can do it yourself but you will need a vacuum pump made specifically for this purpose. I use mine a lot.
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Old 12-29-2006, 08:10 AM   #6
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Unless you have speed bleeders or a pressure bleeder, you need to have someone help you bleed brakes. Looking for 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 12-29-2006, 09:28 AM   #7
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Quote:
Originally Posted by 2000SilverBullet
vacuum pump made specifically for this purpose. I use mine a lot.
LOL...

Highlander picked up a powerbleeder that hooks to the mastercylinder... for bleeding brakes.. it'* the only way to go.
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Old 12-29-2006, 09:40 AM   #8
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Yup, its easy to do, and what i found with mine is that it started to bleed its self





ooo and thanks for the quote Silverbullet
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Old 12-29-2006, 04:21 PM   #9
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Quote:
Highlander picked up a powerbleeder that hooks to the mastercylinder... for bleeding brakes.. it'* the only way to go.
I suppose if you own a brake shop. The last time I had the Bonne brake system flushed at the local Brake shop, that'* what they used. Nice unit if you have any concerns about contaminating the ABS system.

Nice one Bandit......but I have a wife for that.
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Old 12-30-2006, 12:24 AM   #10
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alright thanks for all the help guys...

more questions i just wanna make sure i get this right because after the accident i know brakes are important!

what is the correct way to "bench-bleed" the master cylinder?
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