Brake pedal fading

[prowirenut]

I'm posting this for my dad's truck, he has a bone stock 03 F-250 with the 7.3 and he likes it that way no matter how much I try to get him to modify it he-he-he. Anyway he called me about his brake pedal fading while stopped at red lights. He was thinking master cylinder and I agreed with him. I drove his truck and felt what he was referring to. We took it to a friends shop along with a new master cylinder, they replaced it but the truck brakes were the same.
Now I've learned that the power steering pump drives the hydro booster and I noticed the power steering level was slightly low so we added some, but it acted the same. I sat in the truck with it running, in drive, foot on the brakes and sawed the wheel back and forth and it took about 5 passes and the pedal was to the floor. My question is which direction should we look next, the booster or the power steering pump? I hate to just take a swing at it, any ideas?

 

[florida 6.0]

My Chevy work truck had the same kind of issue . One of the hydro boost hoses was swelling up and seeping when it got warm and I would loose brake feel .

 

[Big Calo]

What does the brake fluid level look like while this is going on?

 

[prowirenut]

The brake fluid level doesn't change at all, we actually changed and purged the lines about a year and a half ago. This problem just started in the last month.

 

[florida 6.0]

Is the power steering fluid burnt ?

 

[prowirenut]

Oddly enough no, he just had a new steering box installed about 6 months ago and the system flushed

 

[Big Calo]

No leaks? Isn't it just ran off the PS pump? I always assumed the PS Pump/hydro booster were the same unit? Seems like maybe a bypass valve may be letting fluid by?

 

[TyCorr]

The ps pump pressurizes the one side of the master cylinder.

If his.master cylinder isnt bad(new doesnt mean good) then the fluid is.escaping. If the hydroboost fails the pedal.becomes impossibly difficult to push with any authority.

The master cylinder is junk or when you let the ps pump get low, it sucked air.

 

[TyCorr]

I would pump the shti outta.the brakes with the engine running and then shut it down, crack the bleeders, and add brake fluid as it gets low. You can close the system and pump it up if you need to.while.gravity bleeding but its not necessary. I let mine go for about 45min and you'll run a qt-qt and half through the brakes. Should be all the old shti=gone. Close the pass side rear then the dr side front. Then dr side rear-pass front. Recheck the fluid. Top up if its low. If the master isnt.shot, that will help. If you still.feel.something is amiss, bleed the ps system. Remove the serpentine belt, remove the.grille, and place a wobble/ujoint on a 2ft extension. Stick a 3/8 allen socket on the extension and shove it in the ps pump pulley center.bore and let er rip. Pay attention to the level of.fluid.

If that doesnt change his whole world, you've got worn components. Look closely at the hydroboost hoses, particularly the one that goes from the master cylinder to the side of the pump.

Goood luck!

 

[rascal]

I have heard replacing the rubber brake lines with SS can help on older trucks. After many heat cycles the rubber lines to the calipers can swell and weaken. THey won't even necessarily leak; they can just balloon.

Good luck!

 

[prowirenut]

Well the solution was finally found for the brake fade problem.

After the local garage replaced the master cylinder, power steering pump and hydro booster they gave up because the problem was still there. My Dad, frustrated at this point, reluctantly, took it to the Ford dealer.

Ford decided to change the master cylinder again and replaced both rear calipers, this of course didn't fix it either. Then they replaced the ABS Module. After that the problem was solved, so in all Dad now has an entire new brake system and he's about $2800 lighter in the wallet. The local garage was nice enough to credit him back for the master cylinder they installed and the labor for it since they couldn't figure it out.

This was a new one on me guys but one I won't soon forget. Please pass it along to anyone who might come across the same problem in the future, maybe save them some money. If your like me and didn't even know where the ABS module lives, it's directly in front of the drivers side battery box, if you look down in that small area you'll see a small box with hard brake lines coming out of it.