Booster or Master? (Update) - 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 09-02-2007, 11:53 PM   #1
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Default Booster or Master? (Update)

Ok here is the scoop on my 95. When I bought the car the guy had it on the rack that day for a master cylinder, rear pads, wheel cylinders, and used front pads on used rotors. The reason he did all of this is because someone told him the brakes were messed up. So I bought it the way he had it set up. This is how they have been till now. Today I decided to put new rotors and pads on it cause the used junk he put on it was shaking the car to pieces everytime you stopped. So I get done put the wheels on and drop it on the ground. Get in and the pedal went straight to the floor for the first say 10 pumps. Now they are better but they are about a quarter from the floor before they start to stop. So they are very soft. So would it be the master or the booster? It will stop if you hit it good but the travel you need to get there is way too much. I went around and bled everything. That didn't help much just a little. Heres a little bit of info on the replacement master. When we were checking out the car on the rack and he was getting ready to bolt the strut tower brace on but he ran into a snag. The new master didn't allow the bar to go back on without unbolting the outside strut mounting pieces because it was too tall. Does this mean I have the wrong master on it? I don't even know if he bench bled the master! I just don't want to replace one to find out it'* the other. Thanks for all the help I have been having nothing but problems lately between the two cars and I am tryin to keep the posts at a minimum and figure these problems out myself.
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Old 09-03-2007, 12:40 AM   #2
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well,if uve bled the lines, and still have pedal goin to the floor, the m/c would be the problem. booster failure will give you a hard pedal. just like havin old-skool manual brakes.

but as far as the wron m/*,do u have any side by side pics of the old and new cyls?

but you should not have to modify the strut mount for an oe replacement(maybe im not fully understanding what u are sayin). i think there was 2 different master cylinders available for you application. one is like 6 and 1/2 inches and the other was like 8 and 1/2 inches. i dont believe theyre interchangeable.
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Old 09-03-2007, 11:09 AM   #3
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Took a look at my '95 SLE. Looks like the strut brace bar would probably need to be removed to easily remove the MC. Here are some pix of the master cylinder in my '95.

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Because you have reason to believe it was not done, I would start by removing the MC and bench bleeding it. That is done by looping two short lengths of line (or plastic tubing and fittings from a MC bleeding kit) from the output ports on the MC to a point well below the surface of brake fluid in the reservoir. You can make your own loops from a couple of line nuts and a piece of bendable brake line. Mount the MC in a vise (by the bolt flange- not by the cylinder); fill the reservoir, then use a dowel to slowly press and release the piston until no air bubbles are seen. Remove the loops and install plugs or blocked line nuts in the output ports. Don't let the reservoir fluid level drain during installation of the MC and connection of the brake lines, or the MC will need to be bled again.

Then bleed the brakes making sure you allow sufficient strokes to move the fluid from the reservoir to the wheel each time. How to bleed brakes That should remove any sponginess (trapped air) from the system.

Then, adjust the rear brakes manually with the star wheel so that the drums are hitting the shoes but not so tight that the drum will not spin. That should bring the pedal up.

If your pedal is still low after this or slowly moves to the floor under pressure, and you can find no leaking brake fluid, then I would agree with the Sam that you have a bad master cylinder.
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Old 09-03-2007, 12:27 PM   #4
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Thanks for the advice. I may just replace the master to make it easy. To explain a little better about the strut tower bar. There are three pieces to it. The bar and two mounting brackets as seen in the photos above (thanks Bill ) When he took the bar off to get the MC out. He unbolted the bar from the brackets and it came out with no problem. However after he put the new one in the brackets had to be loosened almost all the way before the bar would fit over the MC. This is what led me to believe that it'* the wrong MC. I think I will just get one and see what happens. I will post back with the results.
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Old 09-09-2007, 03:21 PM   #5
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I finally have the problem fixed. I found out it was the calipers sticking. The bolts and slides were not allowing the pads to slide easily and this is why the pedal would sometimes go very close to the floor without stoping much, and if you let off and pumped a second time it would be more firm. I replaced both calipers and adjusted the backs nice and firm. The car now stops on a dime when the pedal is at about 50% travel. It will start braking at about 25% pedal travel. So I am very happy to have this fixed for the wife. Thanks for all the info.
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Old 09-10-2007, 10:42 AM   #6
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Calipers sticking shouldn't allow more pedal movement. They actually would fill and then the next time you press them...less movement.

Did you check the hoses going to each caliper for any signs of failure?
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Old 09-10-2007, 11:58 AM   #7
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Yes the hoses were checked and are fine. I also thought the same but it sure stops perfect now. I might even do the same for the 93 since now they feel like it takes too much travel to stop it after driving the 95 for a few days. Maybe it'* the backs that made the difference. I am not sure but it is sure a big time improvement from before.
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Old 09-10-2007, 12:04 PM   #8
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Maybe the extra bleed helped, I've never seen or heard (and logically it doesn't seem possible) of sticking causing a low pedal.

Glad to hear it'* all fixed up.
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Old 09-10-2007, 12:11 PM   #9
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I agree that he may not have bled them properly the first time, plus he did adjust the rear brakes.
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Old 09-10-2007, 06:25 PM   #10
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Well to clarify about the bleeding. The calipers that I replaced I could only bleed from the fitting where the hose attaches due to the bleeders being broken off. So it may have been that there was air in them. Sorry I have everyone confused.
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