Driving home from work yesterday, dry roads, truck unloaded, running around 50mph, had a dog almost run out in front of me. I hit the brakes hard and came to a stop. But, I noticed that my brakes did not lock up the tires. This was a bit of a surprise. My former 2003 Cummins would easily lock them up.

Is my truck an anomaly? Can anyone here lock up your tires during a hard/panic stop?

 

Your old Cummins had hydroboost brakes iirc. Your current truck has vacuum brakes, correct?

Big difference there.

Was your ABS actuating, or trying to anyways?

 

99-03 superduty trucks have hydroboost.
My 2000 doesnt't have abs on front.
Can't lock front wheels at 50, but tires are 295 wide.

 

Not sure when they came out with anti-lock, but would guess pre 2000?
bet you have them...Do you have an ABS light when you first turn the key on ?

and 'anti-lock' means just that, I would guess

sorta self defining - somewhat like that song lyric I heard last night - "I prefer to be by myself when I'm alone"

 

Not sure I've ever heard of that. An engine brake locking the wheels? Never heard of any of the smaller Cummins engines having a brake, but even the engine brake on the big ISX won't lock the wheels of a truck unless you're bobtail in the rain.

My '00 Excursion was on the same chassis that your truck was, and the friction brakes would not lock up the wheels on dry pavement. Brakes improved in newer models though, both my '08 F250 and '11 F350 would. But those were diesels with hydroboost brakes.

 

Some clarification...

First, when I said that my 2003 Cummins would lock up the brakes, I meant that the braking system on said vehicle would lock the brakes. I did not imply engine braking would accomplish this.

Second, both my 2003 Dodge and my current 2003 F350 have anti-lock brakes. I know this for a fact. When the brakes on the Dodge would "lock" on dry pavement, the ABS system would immediately kick in and start modulating. My F350 didn't even get to that point yesterday. No locking of brakes, no ABS modulation. On icy roads, yes the brakes will modulate on the F350.

So...driving down the road, unloaded, dry conditions, panic brake, pedal to the floor (or as far as it will go, anyway) -- I should NOT expect the wheels to lock on my F350?? Is this a true statement?

 

Yes, I believe that is true. I was never happy with that level of performance, but that was the best I got.

 

I made the same incorrect assumption!
I have ABS...on the rear.

Which is a retarded idea. It's not even wheel specific, it runs off the vss in the diff.

The whole point of ABS is not to stop sooner, but to be able to turn while breaking and avoiding locking the front wheels.

Why would you put ABS in the rear only is beyond me.

 

Incorrect how pray tell Antilock Braking System (ABS) does just what it says, stops the wheels/tires from locking up - which is what was posted... no more, no less...


and why they put it on just the back in some cases is, as usual, follow the money
cheaper... the unloaded, light rear WOULD be the first to unload when the front end dives and lock up / skid.

usually sliding wheels have limited resistance to sliding sideways, not necessarily in the direction you want .

 

You speak through, ABS is just what it is - anti lock brakes.

Except, having them on the rear is useless.

 

My brakes wouldnt lock up on wet pavement...

 

After much researching today, and tinkering with the truck (with my 8yo daughter's help), I've pretty much determined that the lack of braking force is a result of the 5 rubber hoses flexing/bulging when hard pressure is applied to the pedal.

I've bled the brakes in the last month or so (I bled them twice, actually). There are new pads at all 4 corners within the last ~2k miles. I've pulled the master cylinder off and performed the brake pin adjustment that's on FTE. The brakes engage right about where they should in regards to pedal application. But I can continue to push the pedal to the floor. When I'm out driving, there's good braking force under hard pedal application, but I cannot get the tires to skid at all.

With the truck parked and my daughter pressing on the brake, I put my hands on each of the 5 rubber lines and I can feel them bulging a little bit. Add up the combined bulging for each of the 5 hoses, and I can easily see how/why the pedal will go to the floor without the tires skidding.

I'll be looking into replacement lines -- preferably DOT-approved braided stainless.

 

I don't think that's true. The only way flexing brake lines would affect this would be if your brake pedal was reaching the end of its stroke. That's because bulging brake lines aren't going to limit pressure reaching the caliper pistons. They will, however, require more fluid volume as they expands. So if they are expanding enough that the pedal reaches the end of its stroke and can't provide more volume then new brake lines may fix things.

Everyone I've heard about whose replaced with braided steel lines has reported increased responsiveness while braking. I don't remember any of them reporting increased maximum braking power.

Prove me wrong though. I'm interested in your results.

 

Antilock brakes do more than enable you to steer while braking heavy. A locked up tire has less traction, especially as the rubber gets hot from friction and picks up debris, etc. A tire that brakes hard, yet is still able to maintain the maximum traction, will stop you better. If you notice, when you brake super hard, you can feel and hear the ABS system modulate the fluid pressure, as it judges the speed of the wheels turning. It increases and decreases fluid pressure to maintain the maximum traction and control. It worked- you were able to stop and maintain control, correct?
As far as rear ABS only, it takes far less braking pressure to unload the back tires than it does the front, so in a hard-brake scenerio, the rear is the more important of the two to control.
Personally, I prefer no ABS. I'd rather control the braking, than not be able to lock them up completely. I've been towing a load before, on a slick surface (say, going slow in mud), and had the ABS reduce braking pressure when I need it. I know that the ABS is disabled when engaged in 4WD, but I wasn't in 4WD, and at that moment, I wanted total control of the brakes.
I don't think it is your hoses- I bet that when you change them, it will still brake the same, if all conditions are replicated.

 

Tom, as I was out driving yesterday -- really concentrating on brake force vs pedal application -- what I noticed was that the braking force was about the same with the pedal down about 1/2-3/4 way as it was with the pedal all the way to the floor. And, yes, I can indeed push the pedal all the way to the floor. My 8yo daughter could also push the pedal all the way to the floor.

I've got to do something, I'm unsatisfied with the performance of the system as it is today. And given the data/info I have, replacing the brake lines seems the most reasonable action. I'm nearly certain there's no air in the lines, the pads are fine, the master cylinder is in good condition visually and doesn't seem to be exhibiting any fluid back-flow under brake application. All signs point to the rubber lines, IMO.

I'm a data driven guy, so maybe I'll use my Torque App to graph acceleration forces vs. brake pedal application.

Regardless, I'll post up my results when I get them.