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

[redmondjp]

. . . 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??? . . .

So you are saying that with the cover off of the master cylinder reservoir, you are seeing bubbles when the brake pedal is released? Often if the pedal is released suddenly, a surge of fluid comes back into the reservoir through the small hole in the bottom and it will cause bubbles to form on the surface as the fluid stream splashes back down.

Or, are you seeing actual bubbles coming from the hole at the bottom of the reservoir? If so, THAT is a definite problem which indicates air still in the system.

 

['94IDITurbo7.3]

So you are saying that with the cover off of the master cylinder reservoir, you are seeing bubbles when the brake pedal is released? Often if the pedal is released suddenly, a surge of fluid comes back into the reservoir through the small hole in the bottom and it will cause bubbles to form on the surface as the fluid stream splashes back down.

Or, are you seeing actual bubbles coming from the hole at the bottom of the reservoir? If so, THAT is a definite problem which indicates air still in the system.

soory about the lack of clarity. i get bubbles inside the mc when the pedal is released.

 

['94IDITurbo7.3]

i have been doing more thinking about what we did with the brakes while the truck was at school last spring....

like i said before we pressure tested the mc and that showd good.

we also hooked two pressure gauges up the the two ports on the mc, thus eliminating the rest of the brake system from the equation. with that set-up the mc held pressure, front port 2,000psi, rear port 1,000 psi. that tells me that the mc is good and the prop valve on the mc i working as it should.

with the two gauges hooked up to the mc the pedal height was also increased noticably and the pedal did not fade down. the pedal had a nice feel to it.

 

['94IDITurbo7.3]

here are some vids

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engine off pumping brakes^^^

 

[D.A.V_Oil_Brnr]

Wild Idea

Ok, after beating my brain til my head hurts (yes I really do have a headache), I have come up with this :

Is it possible that the Master might be bad, but not like we have all theorized in this thread? By that, I mean the actuating rod/valve in the skinny section of the MC. Could it be that the pressurization rod is allowing fluid to slip by causing a soft pedal???

Never in my life have I seen a situation where brakes are soft with the engine OFF. It's just not possible unless the system has no fluid, there is air in the lines, or there is mechanical damage. It's like saying plate steel is soft COLD. Makes your head hurt trying to figure out how it would be possible. The Brakes get hard from the pressure of the fluid in the lines. The only way NOT to have pressure at the pedal is fluid or mechanical damage related issues. That really is the only way. As far as the MC whooshing, it sounds like the MC is making a train whistle noise like its at the end of its extension. The beginning of the whoosh noise sounds as if air is pressurizing in a system, not like a system is damaged. (example, empty air tank with valve hooked up to air tank with 100psi. Turn valve, you hear "wwhhoooooooooooosh" as the air rushes in.)

I really want this figured out. Bugging the crap out of me. When I was in high school, I had an automotive instructor named Wolf. He taught us that the most important part of any vehicle is the brakes because "you can get any vehicle to move, but how do you stop it..?" It stuck with me, and thus causing me aggravation at not being able to fix this issue

 

['94IDITurbo7.3]

sorry for the headache.

thanks for the willingness to stick with it.

later today i will check the booster pushrod length again.

 

[redmondjp]

Yes, it's absolutely possible that your master cylinder is bad. The quality of remanufactured or "new" master cylinders has declined over the years as has been pointed out earlier in this thread (which is absolutely mind-boggling IMO considering the critical nature of the part).

But you mentioned earlier that you had bubbles coming up in your fluid reservoir - this would indicate that you still have air in your system. You first have to get all of the air out. If then, you still have soft pedal, I'd say that it's time to replace the MC.

 

[Thatguy]

can I post a link from another forum that may help with this problem?

 

['94IDITurbo7.3]

can I post a link from another forum that may help with this problem?

by means. yes

 

[Thatguy]

never been a fan of 2 man bleeding. I cam across this a few years ago and use this method for brake bleeding and have never looked back

http://www.fullsizebronco.com/forum/showthread.php?t=140620

build one of these and bleed your brakes. after reading this thread I am leaning towards air in the lines or you got a bad MC off the shelf.

 

[oldmisterbill]

With no RABS valve & no fluid leak - it is likely as has been stated that you are dealing with air ,or a bad master cylinder. A couple points a bad RABS can act just like a bad master cylinder. ( said this for the benefit of others) I had 2 bad rebuilt master cylinders in a row. It is easy to screw up when bleeding brakes ,the person on the pedal can let up before the bleeder is closed (communication problems) its a common mistake to bleed to long and empty the master allowing air to follow the fluid into the lines.

With out a pressure bleeder this is how I do it.

I remember bleeding my braked (CC dually) they can be difficult. there are different theorys on rake bleeding. My preference is to open all bleeders ,fill the master and let it set a bit (keeping the master full) of course bench bleeding helps a lot too. next I close the valve ,refill and have someone run the pedal for me, Open pedal down-close pedal up-open pedal down.This gets the quick easy air out. Then I have them pump it up a couple times & hold down, open valve -close valve -pump up and hold,open & so forth. Remember to start with the furthest wheel first working your way home. Don't be afraid to have the helper push down slowly & tell you what he feels ,the feed back can be helpful. You should see air at each wheel & bleed till you can't get any more ,then go on to the next wheel. If you can't get any change in the pedal during this -I would recommend trying a new master cylinder.

All through this process make sure you don't empty the mastercylinder (that would make all your efforts wasted).

I just hope I have covered every thing & would appreciate it if anyone can correct or add to this.

Mr Bill

 

['94IDITurbo7.3]

with the two gauges hooked up to the mc the pedal height was also increased noticably and the pedal did not fade down. the pedal had a nice feel to it.

Wouldn't ^^^^ indicate a good mc?

i agree with you guys that it has to be air or bad mc, but it is hard for me to think that after bleeding 1.5 gallons of good brake fuid threw the system that there would still be air. that is a lot of frickin' brake fluid. we blead at each wheel until we got only fuid out.

 

[D.A.V_Oil_Brnr]

Mister bill

No, mister bill,

That is correct. It's how I do it. It's also what i posted earlier int he thread.
without actually being there, it will be difficult to figure it out... I offered to speak to 94 over the phone, but my phone has not rang.... ~shrug~

 

['94IDITurbo7.3]

No, mister bill,

That is correct. It's how I do it. It's also what i posted earlier int he thread.
without actually being there, it will be difficult to figure it out... I offered to speak to 94 over the phone, but my phone has not rang.... ~shrug~

I did get your PM. thank you. my biggest problem right now is that i don't have anything else to drive to school and i need the truck everday during the week so i can't tear into it. seems like anytime i try to do anything that "should" be simple turns into a 3 weeks later kind of thing.

 

['94IDITurbo7.3]

i really wish i could get my driver's side drum off so i could see EXATLY what is going on. when the truck was in school that drum came off fine but somebody else put it on and now i can't get it off.