Hi. New to posting on this site but have referenced it Alot. I have an 05 250 xl club cab (not king) 5.4l. 110k. Brakes have been deteriating. My father Owns a mechanical shop so we fix it ourselves. First we did a new booster and master. After a while still had a problem. Warranted the booster. Stiff pedal. Replaced front calipers hoses and pads. Still no luck. Checked out the rear and drivers side axel seal was leaking covering the entire unit in grease. Fixed seal and went to replace pads an realized that pass side caliper was rusted ( drs rear was replaced at some point (appears)). So. Looking at it I need a third caliper and the peddle is still stiff so I am going to warrantee the master. I'm just venting and hoping that Somone will see this and offer weather I'm on the right track or not or of there is somthing iv overlooked. Thanks in advance. Matt

 

If by "stiff" you mean the brakes seem to require too much pedal pressure, maybe you're not developing full vacuum for the power assist?


While no one wants a stuck caliper, I wouldn't think it would make your brakes feel "stiff"...

 

On re-reading, I guess I should clarify. Since most braking, especially when empty, is on the front axle, I'm not thinking a stuck caliper on the rear axle would have a dramatic effect when the front brakes are working fine.


You're sure your brakes are "stiff", meaning "hard"? Or do you mean that you have to push the pedal a greater distance than you think is right?

 

Yes. I was told if I remove vacuum hose and plug it and peddle feels the same then I'm not recivimg vaccum At that point I'd need a check valve or new booster. Again

 

Ugh. I'm pretty sure I need a new booster as when I start the truck w brak on peddle tee is no difference as well as when the vaccum hose is removed and plugged. Stiff peddle all the way around. As in hard to depress. I'd equate it to pressing the brakes for a normal stop and then pushing it another few inches. That peressire and stiffness I get from the get go.

 

Warente another booster *

 

The common mechanics check for a bad booster is to apply the pedal several times without the engine on, then while holding the pedal down start the motor. If the booster is good the pedal will drop away from the vacuum booster working. No drop, bad booster.



With rear disc brakes and dynamic proportioning on vehicles, that information is out of date for more then a decade.

 

Yeah ik. Pedal doesn't change. Bad booster. Again.

 

Thats rare make sure everything else is ok also..



Dick

 

fmtrvt -

I definitely accept that modern developments do attempt to distribute the braking load to all four wheels. However, the vehicle is on springs, hence is not a rigid body, and its inertial center will shift forward as the brakes are applied, regardless of whether they are applied at the front, rear, diagonally, or proportionally.


The only technology that would prevent this shift of weight forward, would be one where the level of water in a glass inside the cab would not tilt as the vehicle is stopped. We're a long way from achieving that.


Nonetheless, thanks for your help to the OP with this problem. Reps to you!

 

Ik. It does seem odd but there is deffintaly vaccum and there is no change with the line connected or w.o. I don't understand. It has to be a booster. Basically everything else is new other than rear hoses and a fairly new master.

 

I'm buying an led light bar this week. I hope truck runs and drives before then :/

 

Brake torque output is a function of coefficient of friction and applied pressure. Most braking is at 200 psi, but if a driver is applying 750 psi of pressure to stop the vehicle at a moderate deceleration, how is moving weight around back to front changing that basic function? The foundation brake is only going to produce x amount of torque at 750psi, it doesn't care if there is 3000 or 5000 lbs of weight over it.

 

It seems to me that those arguments only relate to a uniformly dense, rigid body, which a truck isn't.

My empty truck - and this argument relates to an unloaded truck -weighs around 6,000 pounds, where the front "axle" probably weighs 3500 pounds and the rear maybe 2500 pounds due obviously to the location of the cab and motor.

As the chassis slows down with application of the brakes, the cab compresses the front
coil springs, lowering the front, even as the rear tends to rise up. This changes the body angle, placing even more weight on the front axle/ brakes.


I don't believe I've ever heard of a vehicle, where when you hit the brakes, the nose rises, though I've driven quite a few where the nose "dives". The OP was questioning whether a "stuck" caliper on his rear axle would manifest itself as "hard" braking.

It was, and is, my opinion that if the two front brakes were functioning well, they would be perfectly capable of stopping the vehicle without particularly "hard" braking. I.e., In the "old" days you could drive (and stop) perfectly fine for weeks and months after your rear axle seals first bled oil onto the rear brakes.


As to the coefficient of friction of the brakes being independant of the amount of weight on an axle, I would expect the amount of friction a tire can develop against the road is directly related to the downward weight/force on the wheel. If all of the weight of a vehicle/structure is on the front wheels, the rear axle wouldn't stop a feather!

 

Also. Called napa support. They said I should check vaccum leak. I'm getting 20 w a gauge at the booster. So. Looks like forget napa and need a ford booster.