Faulty Master Cylinder? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-28-2007, 01:27 PM   #1
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Default Faulty Master Cylinder?

1990 LeSabre, 80k miles, I think its all original parts, this is my sister-in-law'* car.

My brother and I replaced the pads and calipers about 2 months ago and at that time we also bled the entire system as the fluid was very dark. It braked just fine at the time. However, now it doesn't. With the motor running, the brake pedal will go down all the way to the floor with very little resistance and the car will not effectively brake. The fluid is also very dark and it seems like it has gotten low in the past couple months.

First I suspected bad wheel cylinders but upon inpsection I don't see any major leaks. One does appear to have some very slight weeping of fluid, but not nearly enough to justify the fluid loss that is showing.

Next, I was thinking the MC was bad. This car wasn't really treated well by previous owners and I'm thinking the fluid hadn't been changed in a long time and perhaps the old fluid and debris from the original rubber sections of brake lines have maybe damaged the mc.

Howver, I don't see any weeping of fluid where the MC meets the vacuum booster. So I really don't know where the fluid is going, other than the tiny leak at the rear wheel cylinder... but even that may just be water that got splashed up under the boot as no extra fluid comes out when the brakes are pressed while in the air.

Any thoughts? Right now I'm wanting to replace the MC and the rubber lines and possibly both wheel cylinders. Then I'm wanting to rent a vacuum bleeder from Autozone and bleed all the old nasty fluid out of the system. Does this sound like a reasonable plan of attack or am I missing anything?

I've replaced the MC, wheel cylinders, and lines on my LeSabre T Type before so it should at least be faster to do this time on another car.
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Old 12-28-2007, 02:39 PM   #2
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Just took the front wheels off and found out that the new caliper I got from Autozone is toast. I originally had O'Reily parts but the pads didn't fit in the calipers correctly and the bleeder screw snapped off so that got sent back. But the Autozone unit is leaking fluid and looks like it locked in the open position causing the pads to rub against the rotor all the time....gah....

-1 fried rotor
-1 fried set of pads
-1 leaky, stuck caliper

We're taking it all back and hoping to get new parts under warranty. Looks like I found the leak and the cause of the soft pedal...

I think we're going to go ahead and replace the rubber lines while we've got it all apart anyway.
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Old 12-28-2007, 08:55 PM   #3
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Yeah Eric, replace the rubber lines while you are there..

Sometimes Autozone can be the worst for parts..

Wait let me rephrase that...

The Quality Control on their suppliers parts is lacking

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Old 12-28-2007, 10:17 PM   #4
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Heh... yeah, certain things are ok from autozone and others are not.

I think we got pretty much everything but the pads and caliper (replaced on warranty) from Napa (wheel cylinders and lines). Napa has good stuff
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Old 12-29-2007, 03:32 PM   #5
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Doesn't look like this forum has been getting much attention lately.... must be the holidays :P

Anyway, just an update as to what we ended up doing:

-new rubber brakes lines front ($14 ea) and rear ($9 ea), NAPA parts
-new duralast gold pads replaced under warranty from Autozone
-new drivers side caliper replaced under warranty from Autozone (last one leaked...grrr)
-new drivers side rotor from O'Reilys ($16), old one was toast from the caliper locking the pads on it
-new rear brake wheel cylinders ($6 ea), NAPA. Old ones were leaking just a tiny bit but when I pulled them apart they had lots of grime and debris inside.
-A thorough bleed job-- we went through about 2 liters of fluid, plus whatever we lost when the old rubber lines were pulled off... lots of crap came out of the system when we bled it so now it should be pretty clean.

About $100 in parts and fluid and my dad bought probably $40 in tools as we needed a weird reverse torx socket to get the wheel cylinders off as well as flare nut wrenches to properly loosen the fittings without knackering them up. ... I would have spent about half that in tools but my dad likes expensive stuff (that he'll probably never use again... *sigh*)

Definately not the way I wanted to spend my Friday, but whatever. It did take all day to collect parts, tools, and actually do the work but at least the car stops properly now. As an added bonus I might be getting the car here in a couple months anyway... I'll probably just let my girlfriend or my mum use it but we'll see.
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