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.

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