Why does my break pedal stay to the floor sometimes when I'm only slowing down?

lahiett
10

Asked by lahiett Dec 04, 2012 at 10:22 PM about the 1991 Buick Park Avenue 4 Dr Ultra

Question type: Maintenance & Repair

9 Answers

lahiett
10

Already checked master cylinder, wheel cylinder and power booster. All good.

1 out of 1 people think this is helpful.
John Saffrahn
14,845

Bleed the system? All the rubber hoses are good? What do you mean stay to the floor? You hit the brakes and the pedal goes to the floor or you pick your foot up off the pedal and it stays on the floor?

nascar24
115

If master cylinder has more than 100k on it it is problaby the problem it is bypassing inside

lahiett
10

Hi Mark. I've already put a master cylinder, power booster, wheel cylinders and new breaks on it. The breaks work great. I am slowing down (not stopping) and sometimes the pedal will on its own continue to go to floor as if I'm pushing on it but not and I stop right in the middle of the road.....?? New one on everyone I talked too. It doesn't do it all the time.

John Saffrahn
14,845

Going to the floor on its own makes me think you just might have an over abundance of vacuum in the intake plenum. When you release the pedal engine vacuum could jump as high as 29in but quickly drop back down to around 22 max. If it is staying too high for too long the vacuum itself may be collapsing the diaphragm inside the vacuum booster. Its either that or something inside the car is pushing on the brake, like a floor mat or something higher in the dash. Only way to test for the vacuum is either grab a manifold vacuum gauge and hook it up while road testing or connect an obd1 scan tool to the aldl and watch the map sensor reading when this happens. Either way you have to get it to do it A severely carboned up intake or a sticking idle air control valve or even a combo of both may cause this. If the intake valve is caked with carbon then its safe to say the idle air control is too. Also next time it happens try putting the car in neutral and give the engine a little gas.

John Saffrahn
14,845

BTW I have never heard if this happening either. I am only giving the most logical guess I can. It can't be the master cylinder or anything after that because the brake boosters internals wouldn't move therefore the pedal wouldn't move. It has to be either the brake booster internals collapsing or something pushing on the pedal from the inside. Did you replace the old brake booster because of this issue, or was it replaced because it was faulty and now this is happening?

lahiett
10

Hi John. I had to replace the master cylinder and power booster two years ago because they went faulty. Now all of a sudden this happend 6 times in two days. But the last 2 days it hasn't done it. There isn't nothing inside messing with the pedal. I'm starting to lean tword the abs control module or abs hydrolic unit or abs lines itself. What do you think? Would it do this if one of these are going bad?

lahiett
10

BTW When this happens I have to put it in neutral and shut the car off to get it to release the pedal.

John Saffrahn
14,845

Abs does nothing more than release pressure from the brakes and reapply that same pressure. You hit the brakes too hard and a wheel locks up, the abs sees it and backs off a valve to relieve slight pressure and then reengauges to put the pressure back on. For any of the abs to become faulty it would disable the abs and would leak internally or the pedal would go all the way to the floor and not stop the vehicle or act completely normal. What you are describing lies in the power booster or the vacuum controlling it. For the pedal to go to the floor on its own means something is pulling or pushing it there. It could even be the power booster is faulty.

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