I have a dangerous situation where my ABS brakes are activating not letting me stop at all. My guess is that the sensors think the wheels are locked up so I cannot apply brakes at all. I started a thread on this a while back with no replies...

Anyway, I need to drive this truck to my shop to fix it. How can I disable the ABS system so that I can drive safely? I tried pulling the fuse (position 15, 5amp) but then it wouldn't let me shift out of park.

 

Pull the plug at the pump?
Aren't you having a problem with "famous" Vehicle Speed Sensor on rear differential?
The $15 part fixed my problems with ABS

 

I do not know, am I? It feels like the ABS activates, and then I cannot apply any brakes at all even with extreme pedal pressure. This is on dry clean pavement.

Is this an easy fix? Here at my house I have basically no tools.

And,,, Sorry I do not know where the pump is. I am sure I could figure it out but some guidance would be appreciated.

 

Follow the brake lines from the master cylinder. They should lead you to the ABS module. Try unplugging the electrical connector from that. You may get all sorts of warnings and stuff on the dash, but it will certainly disable the ABS module.

I wouldn't drive it any more than absolutely necessary that way. And test out your brakes well before you need them.

 

Do you have ABS light on? Any glitches with speedometer? That would be common symptom for bad VSS. There is pretty long topic about it. All it takes to replace it is 3/8" wrench while crawling under the truck.

 

No and No. Everything works fine. I drive (drove) the truck daily and even use the cruise control frequently. No lights on and everything works. The problem I described above is the only symptom.

Except- in case this may be related: I have noticed lately that the steering seems harder- more resistance- at slow speeds sometimes. It is very subtle but I have noticed it 3 or 5 times. I seriously doubt this is related but it is the only other change in anything on the truck.

 

OK. How old is the brake fluid? I had ABS problem on different brand where fluid was pretty old and had semi-solid goo in it.

 

Steering and braking may be related. I don't know if a '99 7.3 has hydroboost brakes or not, but I think it does.

Normally, brakes are boosted by vacuum. Diesels don't make vacuum. On earlier diesel engines, a belt driven vacuum pump made enough vacuum to boost the brakes. On more modern Ford diesel trucks, hydraulic pressure from the power steering system is used to boost the brakes.

What you may be seeing is a power steering pump failure that is causing you to lose power steering and brake boost pressure at the same time. Or, you may be having a failure in the hydroboost system that is causing symptoms in the steering. I couldn't guess as to exactly what is happening, I think you probably want to have it looked at.

 

Sounds like more than my shop full of tools and duct tape can diagnose and fix. To clarify- this is an intermittent problem. The brakes work fine one minute and then the "ABS feel" (rapid pumping and resistance) will be in the pedal so much that I cannot apply any braking at all. Logically this seems like an ABS malfunction to me, not a boost issue. But either way it is sounding like the dreaded trip to the dealer is in order. I have searched this forum and the internet in general for days now and cannot find the same problem duplicated and solved.

 

Here's where I would start, http://www.superdutypsd.com/power_steering_flush.php, easy enough to check and cheap if it works!

 

There are a few ways to disable the ABS, and unplugging the pump itself might not be a good idea, depending on how smart the system is (it should be smart enough to know, but who knows).

Just pull the ABS fuse. Do you have four-wheel (three channel) ABS or just rear-wheel ABS?

If it's four-wheel, it sounds like you have a sensor in the front that is not sensing wheel speed. That can be for a number of reasons. A bad wheel bearing can cause it.

If you have a digital volt meter that can read .1-.3 volts, put it on AC volts. Jack the front wheels off the ground, and disconnect the ABS sensors. Put the volt meter on the sensors, and spin the wheel by hand. A pretty quick spin should generate around .2-.3 volts. While the wheels are up, make sure the wheel bearings aren't loose.

 

My truck has been doing the same thing, as long as the ABS light is on brakes function as they should, if the light is out hold on as it becomes dangerous trying to stop in the last 20 feet, as stated it acts like your on ice or show when your on dry pavement, I have check and cleaned all the sensors, they all checked OK on the AC voltage test stated in other forums. I also flushed the power steering/brake booster. Any suggestions?

 

Did you ever find the problem??? I am having the exact same issue and i cant figure it out.

 

Holy old thread... I had this problem with my F450. The speed sensor wiring harness plug on the rear differential housing was damaged. i replaced the pigtail and sensor and that fixed mine. Hope this helps.

 

The OP had this 7 years ago but since the internet is forever...

You could have shavings on your ABS sensor/tone ring. I've pulled my hubs off a few times and there has been a buildup of metal shavings on the tone ring and sensor. Cleaning this off could help. Obviously you want to find out where the metal shavings are coming from but that could temporarily resolve an ABS issue.