1985 Grand Marquis brake loss

REX FERAL

MEMBER
1985 ALL OTHER MAKES ALL OTHER MODELS

I was recentley driving my 1985 marquis and went to apply the brakes the pedal reacted like normal then all of a sudden gave out and went to the floor and the brake dummy light lit up on the dash. When the pedal is close to the floor it I have brakes somewhat and seem to still have full braking powerif I press down on it hard. The brakes resevoir does not seem to be losing fluid and was not able to find a leak of any kind. ( This does not mean that there isn't one as I live in northern maine and can not spend to much time under the car searching). I checked the regular culprits, the front brakes, rear brakes, and the cylinders. Any help would be appreciated.

Thursday, February 22nd, 2007 AT 6:36 PM

2 Replies

CHEVY22

MECHANIC
1,375 POSTS

There are several things that could be causing your problem,
1 master cylinder is bypassing
2 leak at one of the wheels, either a caliper or wheel cylinder
3 leak at a brake line

if the res is full and there are no external leaks I would suspect the master cylinder bypassing internally, you can clamp off all four rubber lines (one to each wheel )and see if the pedal is the same to isolate the m/c, its not a real high tech check but it works in a pinch

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Thursday, February 22nd, 2007 AT 6:42 PM

MERLIN2021

MECHANIC
17,250 POSTS

Probably the master cyl. But could be the propotioning valve. Must bleed the brakes with valve either puhed in or pulled out depending on bleeding sequence instructions.

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Sunday, March 4th, 2007 AT 7:59 AM