1998 Ford F150 - 5.4L Low Brake Pedal

[nickscarcare]

A family member has this truck which intermittently will have a low pedal usually the first time in the morning when you drive the truck or after it sits for a while.

I thought possibly bad master cylinder and so did he, but after replacing it, it will do the same. Sometimes it don't do it first thing, like yesterday didn't do it for him for the first 30 miles of his drive, he stopped to drop the kids off at daycare, came out and as he was backing up it did it. Pedal goes way down, let up and it will be ok, he just missed an electric pole the other day turning a corner, and went in the ditch. Last night I was trying to get it to act up, drove for a while didn't do it, then as I went back to my place, as I backed out of the driveway it dropped, let up and all is good. It does not give a warning. He just called and said this morning it didn't drop at all, but the pedal pushed back at him. I didn't get to talk to him as I was on the phone, he left a message so that is all the description I got on that.

Anybody seen something like this? No lights on in the dash, but am still questioning the abs unit maybe?? Bad rear drum return springs? Sticking wheel cylinders??

[steven kiser]

Look at the rabs valve. The way you describe it sounds just like one.

[nickscarcare]

Is that the one that screw onto the master cylinder port, or I am thinking its the one that is the proportioning valve.

[ricmorin]

Usually on the frame rail.

[steven kiser]

If this is in the time frame i'm thinking of there were three common issues with these trucks. A bad rabs valve (like ric said it's on the frame rail under the drivers seat) this usually solves the intermittent brake fail. When you replace it it's best to pressure bleed the system so make sure the bleeder screws open before you throw out a price. It's been my experience that the O.E.M. remans aren't any better than the ones supplied by a reputable parts store. When i quote a replacement valve ( since i'm in the north east and accustomed to rusted or salt rotted issues) i always figure in lines.

The abs system in this time frame will make the truck roll through intersections if it's loaded. No not the driver tina . If the truck is even close to it's designed weight load it will roll along while the driver is screaming and using two feet to try to stop it. Telling people to release the pedal and apply again while this is happening gets you blank stares. I've also run into issues (rare) where the fire wall is cracked were the booster mounts. I've seen this two or three times. This is caused by the two feet scream brake application. After all this is done and the customer still complains of a low brake pedal we would extend the piston ram from the pedal to the booster. I had a box of long nuts, again i feel i'm opening myself up , i would remove the ram, cut it in 1/2, tap the cut ends into the nut and weld it. I would extend it approx 1/4 to 1/2 an inch. Don't screw with the ram from the booster to the master cylinder. I guess since there is are huge Ford, Chevrolet, Dodge, Toyota dealers within 1 mile of my shop and i'm within 5 miles of the Auto mile (about 15 dealers) vehicles hit me in waves. When the Ford dealer has a huge push for sales and cut prices and will beat any other manufacturer and keeps pushing for a long time i'll see a drop off for certain customer and they come flooding back when the warranty time runs out. Enough for me.......

[nickscarcare]

This truck is fixed. It was a caliper, brake pad issue. I got to looking real close, and the left caliper had what looked to be dampness on one of the pistons, the guy then informed me that he had replaced the right front a 2 years ago, but not the left one. I told him we had to try that, and as we took it apart the brake pads fell apart also. New pads and caliper and he has not had a problem since the 7th. Must have been sucking air or the pad just moving enough to give that drop in the pedal.