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Pages: 1

Hard Pedal - No lights on - Calipers Grab

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Posted by: MarkVIIDieselGuy

On my 1985 Mark VII LSC 5.0, I am having the "hard pedal" syndrome, and in addition to that, the front calipers grab. There are no brake or abs lights on. I took it to Pep Boys that is close to me, complaining of the caliper grab that would almost jerk the car off the road at highway speeds. They told me I needed new calipers, rotors, pads on all four corners and two front tires, as they were old. After that it seemed fine around town, but when you brake at highway speeds it becomes a scary ride. Sometimes it pulls hard, as if one wheel is braking drastically more than the other three and other times while driving one of the calipers seems to grab causing the whole car to shake so much you have to pull over. I took it back they said everything it fine, that I was obviously not used to a vehicle while airbag suspension (I knew I was in trouble from that point) and that what I was reacting to was the dive of the front end that more severe in an air bag suspended vehicle. After going around and around with the tech, I asked for the service manager. Took him for a ride and he agreed it was some other issue. They looked at the car (or pretended to) then said I needed a $1,200 master cylinder plus labor(yes, I know they can be had for less). So feeling like I had just spent hundreds of dollars on all the brake work I didn't think it needed anyway, I left pissed off. I found a used master cyl assembly that was supposed to be working and installed it (I am far from a mechanic), it worked well for a day, then everything went right back to the same way. The car has been sitting for a year now, only starting it and driving it around the block when I remember to. I know the accumulator can cause the hard pedal, but can it also or is it likely to cause the caliper problem?

Posted by: One_Way

Has anyone flushed out the old brake fluid? There is a specific method of doing this to our M7's.

This might be a good place to start.

Posted by: MarkVIIDieselGuy

Well, I would hope they did that when they did all the other brake work, but considering what they did and who did it, my guess might be no. Is that something I can do myself as a party of one? Thx

Posted by: LincMark_7&8

It is the whole master cyclinder assembly that includes the master cyclinder, accumalator and pump motor. I had it replaced on my 1990 Mark 7 and they bled the whole system.

Posted by: MarkVIIDieselGuy

I did the replacement of the assembly, it was pep boys who did the other work. I guess I need to have the brakes bled properly. Is it something one person can do?

Posted by: LincMark_7&8

According to the manuals that I have read it is a complicated process.

Posted by: One_Way

Quote:

Originally Posted by MarkVIIDieselGuy

Well, I would hope they did that when they did all the other brake work, but considering what they did and who did it, my guess might be no. Is that something I can do myself as a party of one? Thx

Best you can hope for is they bled the master cylinder.

The service manual states bleeding should be done with a power bleeder. Most repair shops should have a power bleeder.

Most of the new vacuum flushers, or "Vaccula", require you to suction the brake fluid out of the reservoir, replace with new, then open each brake bleeder up and insert the hose from the Vaccula. The Vaccula will suction the new brake fluid from the reservoir. When clean fluid flows through the hose, close the bleeder and move on to the next bleeder. While the Vaccula is suctioning the brake fluid, keep an eye on the reservoir making sure it remains full of new brake fluid. You'll need to buy one of these contraptions if you want to DIY. The easiest way to do this is (TURN OFF THE AIR SUSPENSION SWITCH), jack the car up, put in on jackstands, remove the wheels, and do one caliper at a time.

I don't remember the fluid capacity of the M7, but it would easily surpass one of the large bottles of brake fluid.

Others may chime in with other flushing methods.

Posted by: One_Way

Excessive pedal effort to stop vehicle:

Source Action
Binding or damaged pedal linkage Inspect and service as necessary
Hydraulic actuation assembly or wiring Get out the service manual!
Worn or contaminated linings Inspect and replace as necessary
Brake system Inspect caliper pistons, restricted lines or hoses, contaminated brake fluid, improper operation of the proportioning valve

Here are some things to start with.

Posted by: MarkVIIDieselGuy

Yep, we went there. Replaced the calipers, pads, lines, pads, pistons, rotors ALL replaced in an effort to correct the problem. Linkage is not binding. Going to get the brakes bled to see what that does. Should most mechanics know how to do this bleeding on a Mark 7? I am also wanting to know if the accumulator can cause the calipers to grab.

Posted by: One_Way

A bad accumulator will cause the brake pedal to be hard and make the car hard to stop. It will also cause the pump to run every time the pedal is applied.

"Most" mechanics today will think the Mark VII is an antique. However, a good shop will have "Alldata" or some other type service manual to refer to.

Let us know how everything turns out.