Brakes.......Or Lack There Of

[D.A.V_Oil_Brnr]

Mystery Science Diesel

How tight does your E-brake get when you engage it? Try having a friend sit int he cab of your truck and press on the pedal with the engine running while you inspect the rubber hoses and the vacuum hose to the master. See if you can find a hose "flexing" too much. Check at the master to see if perhaps the wooshing noise is a vacuum line that looks good.

The thing to remember is that brake lines can get upwards of 1600 PSI.

http://www.autometer.com/cat_gaugedetail.aspx?gid=2525&sid=3

Literally the only other thing I can think of is trapped air in the lines compressing.

The method I use to bleed brake lines is as follows :

1)Rope friend into helping
2) tell friend when "go" is stated to pump 3 times and hold pedal tight until "release" is stated.
3) do step 2 in the following order : right rear, left rear. pause to check master for gunk, bubbles, etc. Continue form right front then on the left front.
4)Double check ALL zerk fittings, lines, etc for fluid, tightness, etc.
5)pay off friend usually with food and drink.

~shrug~ It sounds to me like you did everything perfectly so I am rather confused. I will say this : I bled my lines after I purchased my truck because the fluid was nasty, smelled bad, and had sediment from hell in it. The rear brakes side of the reservoir kept going low after that for a time, but has stopped.

So, as a last step, do this :

With friend in truck with engine running, have the reservoir cap removed from master and watch as friend pumps the pedal repeatedly and see how low the reservoir gets.

After that.. My head has used up its ideas :smoke

 

['94IDITurbo7.3]

i don't know about the e-brake. scared to press it and not have it return.

I will check for the flexing hoses.

I will try your last step as well.

thanks for the input

 

[redneckaggie]

a small amount of whooshing seems to be normal in most of these trucks when the pedal is hit hard but If the mc did not roll an oring internally then yes I would say your booster is bad,

 

[93f250idi]

my 93 did this. replaced everything! had several mechanics look at and came to the conclution that it was the proportioning? valve. dealer only item, like $530

 

[oldmisterbill]

I am confused here. If the pedal was low & went to the floor ,to me that means a hydraulic problem,not a booster problem. In other words - with no boost & your hydraulic system working you would have to be super man to push the pedal to the floor.
These need to be eleminated before you can say "booster".
Properly bled , master cylinder, brake adjustment, system should use no fluid,- a complete knowledgable check of the whole hydraulic syatem is in order.

 

[D.A.V_Oil_Brnr]

Brakes

That is exactly why I posted what I did oldmisterbill. The only way the pedal would be soft with the lines being properly bled and mechanically proper is if the actual pads/shoes are out of adjustment. I have rebuilt enough brake systems to know that one.

 

['94IDITurbo7.3]

i have bleed over a gallon of brake fluid threw the system. i have no leaks, the the rear shoes are adjusted right and the fronts are working properly.

 

[f-two-fiddy]

The rebuilds You buy today are well documented to fail off the shelf. It sounds like fluid by-passing inside the master cyl. Even if the booster was bad, the pedal should be rock hard.

 

['94IDITurbo7.3]

my 93 did this. replaced everything! had several mechanics look at and came to the conclution that it was the proportioning? valve. dealer only item, like $530

so did the prop valve fix your problem?

you replaced the fitting that is screwed into the back port on the MC that feeds the rear brakes.

 

['94IDITurbo7.3]

how bout this one. a NEW MC with resivior, and it apprears it comes with the prop valve as well.

http://www.autozone.com/autozone/parts/Fenco-New-Master-Cylinder-Brake-System/1994-Ford-F250-3-4-ton-P-U-2WD/_/N-j0mu8Z8kn47?counter=0&filterByKeyWord=brake+master+cylinder&fromString=search&itemIdentifier=248455_0_0_6183

 

['94IDITurbo7.3]

here is the prop valve from ford.
http://www.fordparts.com/Commerce/PartDetail.aspx?n=X3NVKEGKWlPMIyhKi699zQ%3d%3d&id=169320799&m=2&search=true&year=1994&make=Ford&model=F-250

but for the price i might as well just get a new mc again, and the fact that i would be bleeding the brakes again.


tomorrow i will start the truck and have my mom hit the pedal while i watch the rubber hoses.

Is there any kind of test to verify if the booster is bad?

the brakes acted like this with the mc that was on the truck when i dot it, then i put a rebuild kit into that mc, and then i bought a new and still am having issues. i guess it could be another bad master but i kind of doubt it, but hey anything is possible.

 

['94IDITurbo7.3]

allright.

i got an adapter this morning so i could change my boost gauge over to a vac gauge. that worked out good.

vac at idle holds nice and steady at ~23inhg.
when i hit the brakes once it hardly even moves. if i hit the brakes repeatededly the vac will go way down but i still have plenty of power for the brakes.
the vac builds back up at a good pace.
so the reman vac pump that i just put on is good.

i had the truck running and my mom pump the breaks and i checked all the rubber hoses and they are not bulging one bit.

when i felt the right front rubber hose i could feel something moving inside the hose, kind of like air. i don't know for sure though.

when the truck is running and the brakes are pumped i can see a good amt of bubbles show up in the back of the MC. ???air???

when the truck is running and brakes are pumped i can also hear the whooshing noise from the booster in the engine bay easily over the engine noise.

i took vids of all this and hopefully i can post them up when i go to my grandmas house tomorrow.

How many pumps of the brake pedal with then engine off does it take your trucks to use the vac up? for me it is 2 pumps and done.

thanks for the help guys.

 

[oldmisterbill]

The lines are not budging ,nor can you feel much because you have no brake pressure. Most likely you are feeling air in the brake line.
As far as how many pumps you have till vacuum is gone ,you will drain the vacuum quickly because you have a long pedal stroke -caused by bad hydraulics.When the pedal is high it will use less air ,thus less vacuum to apply the brakes. I am very confident you are not dealing with a boost problem. But when the hydraulic portion is correct ,then and only then will you be sure.
The whooshing noise will be more pronounced because you have a longer pedal stroke ,thus more air movement = more noise.
The bubbles make me think as said before Master cylinder bypassing. How did you bypass the RABS valve?

"to make sure i understand, if the diaphragm is torn inside the booster on the firewall then the pedal will be soft.
If the brake booster is good and the vac pump is bad i would have a very hard pedal with no power assist.

I will see if i can get a sound clip of the whooshing noise tomorrow."

If your booster is not working for any of the quoted reasons and the hydraulic parts are functioning correctly -The pedal will be hard as a rock,it will feel the same as trying to stop with no engine running.

Concentrate on a hydraulic problem of some sort.

Good luck.


"

 

['94IDITurbo7.3]

i don't have the adapters or the pressure gauge to hook to the mc so i can't do a test to that right now.

i do remember that when the truck was at school last spring we did the pressure test on the mc.

we unhooked the rear line on the mc and put ther pressure gauge to the mc. engine running we got 1,000psi easy and reliably.
hook rear line back up, unhook front line. there we got 2,000psi easy and reliably.
so that test right there tells me that the prop valve on the mc and the mc itself is good.

we did rebleed the brakes after that.

any other way to test the mc?

 

['94IDITurbo7.3]

http://www.oilburners.net/forums/showthread.php?t=50655

the pics of how my rabs valve is bypassed are near the bottom of the page^^^.