I have a 2000 F250 Lariat 4x4, Crew Cab, 156", V10, Auto, 185k, pretty well bone stock with newer 235/85R16 tires. When I am coming to a stop, and hit a bump, the brake pedal goes soft, and feels kind like a vibration in the pedal. I know anti-locks pulsate, and they work fine on the ice. But on dry pavement, if I hit a bump while applying the brakes, the pedal goes soft, and I lose braking effectiveness. I have to get off the pedal, and then hit it again. Afterward, the pedal is firmer for the next brake application or two, and then it returns to normal. The master cylinder seems to be okay, or at least the traditional methods of checking it aren't revealing anything.

So . . . could this be a problem with the anti-lock brakes? The sensors are all clean. The next step I was going to take is to pull the anti-lock brake fuse to see if the problem returns. Any suggestions?

 

I think you'll learn a lot when you pull the ABS fuse. It sounds like they are activating when you hit a bump. If you're not a huge ABS fan, you can just pull the fuse and leave it out.

 

It sounds like it's the ABS. I can't say my truck has done this on paved roads, but my '01 Montana does it often. The ABS activates when braking over "some" bumps and even on fairly rough surfaces. It does feel spongy when it happens.
My truck does the same thing when on bumpy/rough gravel roads when applying the brakes hard and fast.

Also:
I did have spongy and pulsating brakes on my truck when the brake booster was on it's way out. It also made a nasty squeeking kinda noise (like rubber on rubber) sometimes when depressing the brake pedal. I ended up replacing the booster and the master cylinder and that took care of that problem for me.
It felt like warped front rotors when braking at higher speeds. Originally I thought I had bad (warped) rotors, but it turned out to be the booster.
I'm pretty sure I could have gotten away with replacing the booster only, but since the master cylinder was 7 years old and was being removed for the booser replacement I replaced it also.

Rick...

 

Subscribing.....

I have the same prob on my 99 and I DONT have ABS.

 

Yeah my 2001 F350 does the same thing.

 

Thanks for the replies. I got the fuse for the ABS pulled this evening, we'll see if the problem returns. Got to playing around, turned off the radio and the heater fan, and while depressing the brake pedal, I could hear a very quiet "hiss" under the dash. So, sounds like I need a new booster, in addition to all my other problems. Odd thing (to me, anyway), is that I can only hear it leaking when the brake pedal is at one position. Anywhere else on the pedal travel, no audible leak.

 

That hiss is probably just the vacuum power assist booster. No big deal. You'll also hear this noise if you shut the truck off after parking, then press on the brakes.


My '07 does the same thing on bumps while I am braking. As I apply pressure to the brake pedal, I go over a washboard style bump and it fools my ABS into thinking the rear wheels are locking up. You feel the pedal go down quite a bit under your foot. Sometimes you can also feel the "buzz" of the ABS working, but not always.

There is a set of bumps just before my driveway if I am heading southbound. They always fool the ABS. The first time it happened I was a little alarmed, but after a while you get use to it. Now I think of it as an ABS test.

 

I'd suggest stopping by a brake or preferred repair shop before making any costly decisions.
With the "hiss" I would lean towards a leaky booster (I noticed a fairly loud hiss at the pedal / firewall area at certain positions of the pedal when my booster was failing along with the other squeeking noises).

The fact you've noticed the pedal kind of fluxuating a bit might also be sign of the booster failing if not the master cylinder.

Sometimes these trucks can prove to be a real challenge to track down some problems.
A good shop should be able to diagnose it for you with not much effort.


But of course I'm a Canadian,,, I wouldn't trust me either.

Rick...

 

Update time. Got a booster today. Got home, took the master cylinder loose from the booster, and master cylinder is bad. Had fluid inside the booster. Sooooo . . . another call to CarQuest, and have a master cylinder in my hand 30 minutes later.

You know, I never thought the brake pedal was that hard to push. After replacing the booster and master cylinder, holy crap. That pedal requires very little pressure and the brakes work better than ever.

Went to chase down why it is pulling to right when I apply the brakes. Figured it was a stuck caliper slide. It was, lower slide on the driver front was froze solid. Took 15 minutes and a torch to get the slide out of the caliper bracket. Penetrating oil, a stainless steel brush and a cordless drill cleaned everything up nicely. Took it for another test drive, still pulls, figured as much.

I noticed while I had it apart, that the previous owner must have installed a loaded caliper on the driver side, because the pads on the driver front do not match the ones on the passenger front. So, hopefully a new set of pads will fix that right up, but that will be saved for another day.

Thanks for all the advice and tips! I'm going to reinstall the ABS fuse, and see if the booster/master cylinder was causing the soft pedal on bumps issue. I'll follow up when I figure something out.

 

I re-installed the ABS fuse after changing out the m/c and booster. Thursday morning, I opened up the rear brakes to check for sticking slide pins. Got the sticky ones freed up. Best I can tell, the rear brake pads are original!!! And even with the uneven wear from the slides binding, there was still meat left on 'em. The problem, is that the friction material was beginning to peel away from the backings. So, yesterday morning, I put new pads on all four corners. I installed Advance Auto's WearEver Gold pads, and the truck stops so much better -- or so I thought. On the way to the Advance Auto to get brakes for the wife's car, I hit a large bump while applying the brakes. Soft pedal over bumps remains.

So, I pulled the fuse again, and we'll see what happens over the next week or two.

 

Dont be so hard on yourself buddy. Do any Curling?

 

2000!!!! No way. That's amazing. I really should stick with Motorcraft brakes.

 

The front brake pads are original on my dad's '95 F350 Powerstroke, and it has 280k on the clock. Of course, his mileage is by far mostly highway, and he is very conservative where braking is concerned. Yes, it is verifiable, as he bought the truck with 20k on it.

The rear shoes were replaced at 80k, because the wheel cylinders were leaking, and he is still on the set we put on at that time.


Oh, and so far, so good. No soft pedal over bumps since I pulled the fuse. Want to give it another week to be sure, but it is looking good!

 

Thanks for the updates las,

Sounds like you're slowly getting it sorted out.

Rick...

 

Curling is for bald Canadian men and Canadian women that choke when it really matters (silver?,,, choke).

Rick...