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1992 Pontiac Lemans -- poor brakes

Tiny
SQUASHTOWNER
  • MEMBER
  • 1992 PONTIAC LEMANS
Customer complained about poor brake pedal. Exact symptoms of a bad master cylinder. Replaced the cylinder, bled the brakes at each corner, and at all the ports on the master cylinder, and when not running, the car has PERFECT pedal. Better than that of my 2005 matrix. Start the car, and the pedal goes to the floor when you push it, and the car will hardly stop.
We suspected a faulty reman MS (it happens) and replaced it, and did the whole bleeding process again. Same pedal.
Car has new pads, rotors, and recent rear shoes. Rear brakes are adjusted, caliper slides are perfect, wheel cylinders move freely.

Is this the booster? Or could it be those 2 little proportioning valves on the brake lines, attached to the MS?

Thanks for any help!
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Monday, February 6th, 2006 AT 4:27 PM

6 Replies

Tiny
CHEVY350GUY
  • MECHANIC
  • 109 POSTS
No abs?
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Monday, February 6th, 2006 AT 5:11 PM
Tiny
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No ABS.
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Monday, February 6th, 2006 AT 5:51 PM
Tiny
MVANNESSJR
  • MECHANIC
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Check the vacuum lines and make sure they look good. Is there a hissing sound? I would suspect a possible failing power brake booster. There isn't much left if you've already replaced the master cylinder.
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Tuesday, February 7th, 2006 AT 3:37 AM
Tiny
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With the booster vacuum line plugged in, or disconnected, there's a very noticeable"SSsshhhhtttt" sound every time you pump the brake pedal.
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Tuesday, February 7th, 2006 AT 4:49 AM
Tiny
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Oh, and those little proportioning valves re unavailable anywhere, apparently. Our local GM dealership has onle ever had one Lemans in for work in all the time they were sold, and they told us that the car is now classed as "vintage" and parts are hard to come by, if not impossible.
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Tuesday, February 7th, 2006 AT 4:51 AM
Tiny
MVANNESSJR
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Without actually being there and listening to it myself, it would appear that the power break booster has seen better days and should be replaced.
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Tuesday, February 7th, 2006 AT 8:04 AM

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