Brake issue

[BigRigTech]

I've been having a brake issue on and off with my 91. Sometimes when I stop at a light the pedal seems to creep very very slowly, not to the floor but it creeps enough that you can feel it. I've replaced the master cylinder and bled the entire system twice....Here's the wierd part - if you put your foot on the pedal with the engine shut off it's rock hard and stays that way....????

The master cylinder and rear wheel cylinders are off my 96 1-ton parts rig. The W/C's have a bigger bore than the ones I took off but they bolted up ok. I installed them today along with replacing the brake lines on the rear axle. I ran out of time this morning so I have to adjust them up and test everything tommorow or Monday.

 

[Mr_Roboto]

What you are describing is normal. The vacuum pump has much less "volume" of vacuum than a gasser intake manifold that it replicates. When you press the brakes, you use up vacuum then the pump slowly pulls it down more which pulls on the brake booster more and the pedal sinks a little from the additional boost.

Ford released a special booster to eliminate this "symptom" however it is normal and no repair is necessary.

 

[towcat]

silly question.....is the truck a ABS truck? If so, I betcha the dump valve is bleeding down

 

[BigRigTech]

So if I took the booster from the 96 F350 would that fix the issue? It has rear anti-lock, not abs.

 

[tonkadoctor]

So if I took the booster from the 96 F350 would that fix the issue? It has rear anti-lock, not abs.

Rear anti lock is abs ........ or rabs as it's known on these trucks.

 

[Mr_Roboto]

Any booster besides Ford's special "service part" will exhibit the same symptom.

This is copied from Dieselmann's site: "1997 and earlier diesel trucks equiped with vacuum power brakes--Low/creeping pedal:
Many owners have complained of a low or creeping brake pedal on their trucks, often mistaken for a bad master cylinder or Rear ABS valve. If the condition occurs after the vehicle has come to a stop, and no other brake concerns are found, (worn or out-of-adjusted brakes, cocked pads, or hydraulic problems) the condition is normal and the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds it unacceptable. This part is only for use on diesel-equiped trucks--P/N F5TZ-2005-CA--and is not a service replacement; it must be ordered by the part number, not vehicle application."

 

[icanfixall]

Try this... Set the parking brake. If it sets more than half way to the floor your rear brakes are out of adjustment. The rear auto adjusters never really work very well. What you are feeling is the fronts doing all the stopping and the rears slowly filling the w/c. Do you replace the front pads more often than you think you should and do the rotors warp or crack like mine always did? I finally started to manually adjust the rears and my peddle is much higher plus the front brakes and rotors last longer now. Yes, the rabs valve can be bypassing but adjusting the rear brakes is much cheaper than a $200.00 to $400.00 rabs valve. It just depends on where you buy it. As most here will tell you, do the cheapest things first.

 

[BigRigTech]

Here's a test to see if it will let me post...

 

[BigRigTech]

I'll finish it tommorow, the brake adjustment is way off and I ran out of time yesterday - The wifey booked me for some "quality" time in the PM.....Meaning I was her shopping chauffeur....

 

[BigRigTech]

Adjusted the brakes - working A1 now. ...Stops much better than ever before.

 

[Optikalillushun]

Try this... Set the parking brake. If it sets more than half way to the floor your rear brakes are out of adjustment. The rear auto adjusters never really work very well. What you are feeling is the fronts doing all the stopping and the rears slowly filling the w/c. Do you replace the front pads more often than you think you should and do the rotors warp or crack like mine always did? I finally started to manually adjust the rears and my peddle is much higher plus the front brakes and rotors last longer now. Yes, the rabs valve can be bypassing but adjusting the rear brakes is much cheaper than a $200.00 to $400.00 rabs valve. It just depends on where you buy it. As most here will tell you, do the cheapest things first.

this is a great tip, i forgot bout trying this. i glad u broght it up because my 88s parking brake pedel goes to the floor. on my 93 it goes about 1/2 way or a little more.

now here is one for ya...my moms 04 xploder sport has rear discs and the parking brake doesnt work. goes to the floor and nothing happens. no way to adjust it either yay ford...

 

[BigRigTech]

I've always been a little narotic about my vehicles so I tend to check my brakes quite often.