LIncoln Mark V11 brakes

For a few years the brake lights on my 90 LIncoln Mark V11 would come
on during very hot weather but it never affected the brake performance.
When it cooled off, they'd go off. They came on last week and I lost
what seems like the power brakes. They are very cushiony and I have to
press very hard to stop the car. They replaced the ABS unit with a
mustang unit but it only slightly helped. The car is still undrivable
safely. Any suggestions????
lindsncal RemoveThis @aol.com

LindsnCal.DeleteThis@aol.com wrote:
> For a few years the brake lights on my 90 LIncoln Mark V11 would come
> on during very hot weather but it never affected the brake performance.
> When it cooled off, they'd go off. They came on last week and I lost
> what seems like the power brakes. They are very cushiony and I have to
> press very hard to stop the car. They replaced the ABS unit with a
> mustang unit but it only slightly helped. The car is still undrivable
> safely. Any suggestions????
> lindsncal.DeleteThis@aol.com
>
The most common cause of this problem is a failed accumulator. It's the black "ball"
attached to the ABS unit. If the entire assembly was replaced with a used one with a
failed accumulator then you will have the same problem. There is also the pump motor
and it's circuit to consider, including a relay and a pressure switch.
Often failures on this system are progressive. The accumulator starts to fail
causing the pump to run too long and too often shorting the pressure switch. This
eventually causes the pump relay to stick closed allowing the pump to run until it
self destructs. If the relay burns up and no longer closes the pump won't be damaged.
Problems in any of these areas can cause a hard pedal.
There is a Tech article that gives some insight into the Mark VII ABS system here:
http://www.lincolnsonline.com/tech/00021.html. Also check out the Mark VII forum at
www.lincolnsonline.com. Do a search for ABS and you'll find more information than you
ever wanted. There's also a fairly new site: http://www.thelincolnmarkviiclub.org .
Both are fantastic sites with a lot of really good people and a lot of great
information specific to the Mark VII and other Lincolns (I'm biased, I have an 84 and
89 Mark VII).
It's not a really complicated system but the mechanic needs to know how it works and
what's involved to properly diagnose it. The problem could be as simple as a failed
pressure switch or relay. It could also be as drastic (expensive) as a failed pump,
accumulator, relay and switch. Just a heads up, the accumulators are getting a bit
hard to come by and are fairly expensive, $150-250.