brake pedal goes FLAT..... IT'S BAAAACK!!!!!!!

blackagatha · Post by **blackagatha** » September 27, 2007, 11:16 pm

A'right. this makes zero sense to me...

When I back up a hill (no matter HOW SLIGHT), the brake pedal will go completely to the floor. If I was to be moving quick, I would smash right into something. I have to sit there and pump them up 2-3 times before I drop into drive, or else she runs away with no brakes.

This issue has existed through 3, mark it- THREE master cylinders, of 2 different designs. I am pretty sure at this point that it is positively NOT the MC.
My dad expressed the opinion that my rear brakes were out of adjustment. I checked. I adjusted. I cleaned them out and checked the pads. everything good. everything tight. Still does it.

Seems to be only when I (GENTLY) apply the brakes over a small to long period. If I go fast backwards and SLAM on the brakes (as if to adjust the rear brakes), the pedal is good and firm, brakes bite hard.

It struck me the other day that this issue appeared about the time I installed a knob-type Proportioning valve on the rear line. Is it possible that I have to unscrew it to max pressure, then dial it back down afterward?
Even if so, I can't fathom why the problem only surfaces during gentle application, while moving backward up a hill.
(AND IT IS ONLY BACKWARD. YOU WOULD THINK THAT forwardDOWN A HILL WOULD DO THE SAME THING...wouldn't you?) unless somebody knows a LOT more abut this than me.

Throw me some ideas people...
Thanks.
Frank

Phil · Post by **Phil** » September 27, 2007, 11:23 pm

Is the prop valve installed in the correct flow orientation?

as in; IN from the MC, OUT to the back brakes?

blackagatha · Post by **blackagatha** » September 28, 2007, 12:00 am

yeah. it's installed with the correct flow direction.

Phil · Post by **Phil** » September 28, 2007, 6:11 am

Honestly Im a novice with brakes but I have done a couple disk swaps on other cars.

What brake system are you using?

Stock, disk, all drum?

It sounds like a gravity thing as in a huge amount of air in the lines and teh fluid backflows on a hill but I have no idea how it could only happen in reverse unless there is some residual checkvalve someplace.

Unless is something mechanical due to stress being put on the system, as in body flex and pinching off a hose or something weird.

Any leaks anywhere?

That really is a weird issue

ICEMAN6166 · Post by **ICEMAN6166** » September 28, 2007, 10:36 am

the one thing that comes to mind is the star adjusters being backwards/on the wrong side as there is a left and right. this would cause the shoes to loosen rather than tighten when backing up and gently braking.
you did not mention if this only happens on hills or if it does on flat ground too.
definitely strange but i would check the adjusters.

blackagatha · Post by **blackagatha** » September 28, 2007, 11:31 pm

the system is a '73 econoline or similar MC, knob type prop valve, disk on front- CPP version w/ C#3^y calipers, Stock drum setup on back-modified to work with auto adjusters.

The adjusters are def. installed the right way.

There are no pinches in any lines

there are no checkvalves

there is no power booster

it doesn't matter how slow I go

it has NEVER happened while going forward.

it SOMETIMES happens when backing from the garage (in the back yard), out the driveway and into the street. (the whole way is "practially" flat, but there ARE some very slight bumps

Mostly, it requires a hill. A slight hill will make the pedal go way flat, but there will still be a little bit of brakes left. On a STEEP hill, there will be NO brakes left WHATSOEVER.

I have probably bled the brakes like 15 times minimum at different times since the beginning of this headache.

If it is an air in the system problem, I would assume that I would have no brakes, all of the time.

Like if I squash the hell out of the pedal, I CAN touch the pedal to the floor, but I wouldn't dare do that while i was going fast. I'd lock up all fours and all that jazz.

I've tried to use a mityvac bleeder system, but it was a joke. Don't know why, but it wouldn't work for crap. Doubt if it would make any dif. I believe the system is clean.

blackagatha · Post by **blackagatha** » September 28, 2007, 11:36 pm

oh yeah. I forgot to add. I definitely bled all the air out of the MC in the vise. So that should not be any part of the problem.

shawns fords · Post by **shawns fords** » September 28, 2007, 11:52 pm

ok, I doubt its a hydraulic issue at all, air in a brake system is either there or it isnt, weather your going uphill ,downhill, level, parked, whatever. the system can Aireate itself, and a large bubble of air will turn into a bunch of small bubbles throughout the system and it will still respond the same, (just harder to bleed), what im wondering is if the rear shoes are not installed properly, perhaps primaries and secondarie shoes are opposite the place they should be? that would be a reason as to why the brakes arent working when going up a hill, one shoe has more material than the other, primary vs secondary. I cant even remember which is which right now, im too tired, lol
anyways look into that and see what ya find

fmartin_gila · Post by **fmartin_gila** » September 29, 2007, 8:29 am

With two exceptions,I did the same on my 62, and have had absolutly no problems. I used a MC from a 1970 1/2 ton and a proportioning valve from a 1982 F150. I also got all the hardware and self adjuster stuff and installed on my original backing plates. I can't fathom how your problem could be caused by the difference(if any) in the MC, so that would leave only the Prop Valve.
Is there any possibility of the MC somehow bypassing? Are you adding fluid to front or back? Have you given any thought to getting a Proportioning Valve from a Junkyard for a pickup, and trying it.
Fred

Slick Fan · Post by **Slick Fan** » September 29, 2007, 11:20 am

Sounds like it's time to switch to 4-wheel disc brakes.

Funky problem, for sure.

Ford4jack · Post by **Ford4jack** » September 29, 2007, 11:41 am

do you think a broken mount or caliper pin would do this. It might allow the caliper to cock some and force oil back thru the system since your having to pump your brakes back up after this happens.

Or like Shawn said flipped shoes. Or maybe a broken anchor or pivot pin on the rear.
Have you tried pushing the petal at different speeds just sitting still and see if it varies any.

The uphill thing is weird though. wonder if something's able to free float around in a valve.

How steep of hill does it do this on?.

blackagatha · Post by **blackagatha** » September 30, 2007, 12:13 am

well, last time I checked- like a month ago, and every time before, everything is fastened down tight, in (seemingly) good operating/mechanical condition.

As I've mentioned, it will do it on a hill that is like 1 degree or less (to a slight degree) or complete failure on a much steeper hill. The angle definitely seems to affect the result.

What do you mean "MC bypassing"?

I don't have to add any fluid at all. neither reservoir seems to get noticeacly low at any time, nor does there seem to be any fluid transfer between reservoirs.

The prop valve is a 1 line in and 1 line out. Only the rear wheels are in anyway involved with it. (I say this to eliminate doubt of a leaky o-ring inside the prop valve causing fluid transfer/release)

"Have you tried pushing the petal at different speeds just sitting still and see if it varies any"---- what do you mean by this?
I believe it doesn't happen if I stomp on the brakes rather than push soft
If it is sitting still, everything feels proper. It must be moving for a problem to exist.

yeah. a 4 wheel disk would be an obvious solution, but I don't got the means for that right now. sadly.

Ford4jack · Post by **Ford4jack** » September 30, 2007, 6:38 am

"Have you tried pushing the petal at different speeds just sitting still and see if it varies any"---- what do you mean by this?
Just wondering if there might be a machining defect or crack that was letting fluid pass in the MC but if you already tried 3 of them

I would try what Fred and Shawn suggested.
Try another prop valve and make sure the leading/trailing brake shoes are installed correctly.

Have you tried different settings on your adjustable proportioning valve?

fmartin_gila · Post by **fmartin_gila** » September 30, 2007, 7:13 am

If neither end of the MC is not getting lower, then you may have a bypassing problem. The bowl that is above the end that pushes on the disks should get lower as the pads wear. The adjusters on the back keep the fluid level up on that end, whereas the disk pucks do not return to a relaxed position.
The next time it does this, just sit there for a few minutes holding pressure on the pedal. If the pedal slowly "sinks" down with pressure held on the pedal, you are experiencing bypassing in the MC.
Fred

joeymac64 · Post by **joeymac64** » September 30, 2007, 3:21 pm

have you got the proportioning valve plumbed int the rear brake line also you might require the use of pressure risidual valves 10lbs valve on rear line and 2lbs valve on front line with the proportioning valve on the back brake line.

blackagatha · Post by **blackagatha** » September 30, 2007, 8:25 pm

I should mention that I had this system operating (ie econo MC, rear brakes w/ auto adusters installed, and disk brakes for probably a year minimum, running a prop valve from a crown vic or something. Was having problems with the front brakes and decided to remove any connection between front brakes and p.valve. I installed the new p.valve at that time, roughly a year and a half ago. At some point (relatively soon after that, I believe), this became a problem. I may be incorrect about that time frame, but not sure.

By my comment on the MC juice not dropping... that's not what I meant exactly. Like as the front pads wear down , the fluid drops appropriately, mostly what I meant was that the juice is not pumping out of one reservoir and overflowing out of the other. Nor are there any leaks that I can detect. Nothing coming out of the weep hole in the MC boot.

A residual pressure valve on the rear might make some sort of difference, BUT it seems to me that if the brakes are properly adjusted, why the hell would the system need a resisdual valve? Like I can understand using a 2LB valve on both lines if the MC was under the floor or something, but it's not... And I think that if I put ANY resid. on the front disks, they would never let go... They already don't like to let go... I don't get disk brakes for that reason... they're always dragging and getting hot... there's just nothing to pull them back...

Oh, and you guys talking about the pads being installed vice versa.... NO, that would not, could not cause the trouble I got... It might provide a crappy coefficient of friction, thus not stopping the truck, but it would not, could not cause the pedal to go flat........ ((no offense, but it's the truth))
Anyways, if they WERE backwards, I believe that would IMPROVE (Backward)braking-- They are oriented the way they are to make for better forward braking (right?), due to load transfer between the pads. Thus, in the Correct orientation, the brakes would work better going forward than backward anyways. Not that the difference would (probably) even be evident...

MattsIASlickShop · Post by **MattsIASlickShop** » September 30, 2007, 9:21 pm

We need pictures of the MC/proportional valve area and each wheel's brake area (without drums on) and a company/part # that you have for the MC to get a better idea of what you have. Too many ideas being floated without something to see.
Oh, and confirm that the bleeders are on the top side of each wheel cylinder ( not reversed) My first thought is that maybe you have a drum/drum MC or something like that.
Matt

blackagatha · Post by **blackagatha** » September 30, 2007, 10:52 pm

I SUPPOSE the MC could be for a Drum/Drum setup, but I sincerely doubt it. According to Autozone, It's for a '73 econoline, intended fo Power Brake application (I am using it manual).

All bleeder screws on calipers are perfectly vertical, rear wheel cylinders perfectly stock.

Also, there are no lines above MC fluid level. I've seen on the 'net that That can be a problem.

I will try to get pics asap.

I DID find on a couple different locations an instruction to screw the Pvalve all the way in prior to bleeding. I believe I should do this... I don't think I've ever included this in the bleeding process. Maybe this is a DUH-ME situation. I don't know. Perhaps I need to bleed the system while it's sitting on a hill. I've seen this mentioned also somewhere on the 'net; something about elevating the rear end to bleed troublesome rear brakes.

Ford4jack · Post by **Ford4jack** » September 30, 2007, 11:11 pm

My thoughts on the shoes and calipers were that they might be displacing fluid when being used in reverse.
A shoes or calipers shifting type thing because your needing to pump up the system after this happens.

Seems like if your having to pump the system it would have to be refilling a void on a wheel or in the MC.

Guess your right on reversed shoes for this problem.

Good luck hope bleeding it works for you

MattsIASlickShop · September 30, 2007, 11:21 pm

also, you should have the lines going into the proportional valve like this:
[albumimg]2821[/albumimg]
I am wondering if it could be part of the problem, if the lines are going in differently.