Brake issue.

[90Aero]

I have a 1990 Eddie Bauer extended, 4.0L 2WD, and the brakes work fine most of the time, but sometimes the pedal goes 4/5 travel to the floor, whereas normally it may travel 1/4 before pressure is felt. I have put a new master brake cylinder and the problem has persisted. I bleed all the brakes twice. No change.
I don't get any brake warning light. It happens once and then it works fine for say 8 brakes then happens again. I want to blame the anit-lock, but I have no proof. Its a bit scary when that pedal drops near the end of its travel.

Anyone else ever experience this?

 

[BrooklynBay]

When you bled the brakes, did you start with the wheel which is the furthest away from the master cylinder first?

 

[90Aero]

When you bled the brakes, did you start with the wheel which is the furthest away from the master cylinder first?

Probably not. But it seems to me that its unlikely to be a brake bleed problem since the brakes are hard and firm most of the time then just inexplicably the peddle will go near the floor. Then on the very next brake, its fine again. Its very bizarre.
The manual suggests something wrong with the rear drums. So I plan to pull off the wheel and hub and have a look. But the rear drums don't make a lot of sense to me. Had I not replaced the master cylinder, I would still think it was the master at fault.

 

[Brian A]

did you put a new master on or a rebuilt?

I have had many problems with rebuilds, I dont use them anymore.

 

[90Aero]

Its a remanufactured Cardone brake master from Advanced Auto Parts. But the reason for changing it was this same problem. It seems unlikely that a rebuild would have the same exact issue.

 

[Brian A]

sorry I missed that

Yes, I would have a close look at the rears. You may have a bad wheel cylinder. Sometimes the pistons can corrode in the bore and cause strange problems or may be leaking

does the parking brake work?

 

[90Aero]

THe parking brake cable snapped. I'm working on getting a replacement. I do hear something on the rear brake as I drive and it seems like the rear brake is not 100% releasing. So there is something going on back there.

 

[Brian A]

might be a parking brake strut is hanging up causing you problems

it may be hard to get your drum off

I can give you some tips there if you need

I spent many years wrenching at a Ford delalership and a few brake shops before that

 

[90Aero]

Ok, the results are in. On the drivers side the shoe pad was half missing, as in cracked off and gone. The passenger side had a busted spring(source of the noise). I also found that the wheel cylinders were rusted and leaking every so slightly.
Fast forward, new everything, including the busted brake cable mentioned above. No more noise from the rear brakes and it brakes well. But.....damn if the pedal did not go to the floor a couple of times while I was test driving it.
So to recap, New Master cylinder, new parking brake cable, new rear everything.... problem persists. Seems to me there is only one component left. The Anti-lock.

 

[BrooklynBay]

Since this has RABS, disconnecting the fuse or unplugging the module disables the ABS system. Did you ever get a red or yellow ABS/brake light?

 

[90Aero]

Since this has RABS, disconnecting the fuse or unplugging the module disables the ABS system. Did you ever get a red or yellow ABS/brake light?

No, never any lights.....but then again I have been meaning to make sure the light lights when the ignition is first switched on.
I will try pulling the fuse.

 

[BrooklynBay]

Take a look at the sticky thread on the top of this section on ABS issues.

 

[Brian A]

what kind of shape are the front brakes in?

its possible that you have a caliper that hanging up every so often resulting in the need do a few brake applies to get it to seat against the pad. Make sure the piston pushes back in the bore fairly easily, wheile its pushed back some try to slide the caliper on its mounts, make sure it moves freely and does not **** and hang up, make sure the pads also move freely in the anchor mount. Make sure those pads dont have a crack in them like the rear did, any of this can cause this problem.


Also make sure that the caliper hoses are intact, I have seen the outer layer split, casuing the inner layer to buldge out on a brake apply. And while you are at it, carefully check the condition of all brake lines and hoses, including the one going from the frame to the axle

what shape are your front wheel bearings in?

I have seen a loose wheel bearing cause this too. The loose wheel bearing can cause the rotor to push in the piston in caliper and again, a few brake applies are needed to get it to seat against the pad

As far as blaming the ABS, I doubt that is the issue.

Think about how the abs works. When its not functioning, its just a flow through valve. When it senses brake slip at a wheel, it shuts off and opens a valve to that wheel very quickly. So if it was malfunctioning, it could lock up that wheel, or not allow pressure (fluid flow) at that wheel. Neither of these conditions would cause the pedal to fall to the floor. If anything it would cause a hard pedal and decreased stopping power. The ABS unit has a fail safe built into it, so if it loses power or stops functioning you dont lose your brakes.

The one thing is if there is a valve that hanging up in the locked position, then releases, I suppose that could cause a problem.

The problem with this is, the pedal should still return to the normal positon when the valve releases, not go to the floor.

Sure, you could have air inside the abs unit, that can cause weird things. But since this problem was there before you first changed the master, probably not. Unless you allowed the brake system to become very low at one time. Or the abs unit may have an external leak on the unit itself, I have never seen that but anything is possible on an older vehicle.

Pulling the fuse on the abs circuit is a good idea, its easy enough

 

[jlh3rd]

aero 90

you're not alone, my 92 aerostar has had a similar problem for years, except my pedal usually goes 3/4 travel and seldom seems normal.....even under full braking i cannot lockup the front wheels........you can see my posts on here for all that i've done, and i've done just about everything......sorry this is no help

 

[90Aero]

I verified that the ABS light was working and that it went out after a few seconds. I then pulled the fuse for the ABS. I drove about 3 miles braking on and off the whole way. Its not conclusive, but the pedal never went to the floor. More testing is necessary, but in the past taking this same 3 mile drive, the pedal would go to the floor at least twice.
Other than this issue the brakes are working great, I'm sure I could lock up all four wheels if I wanted.