Brake issues! Help save this rig from going to the scrap yard!

[Anime]

Well think about it this way, if the problem is the pedal going to the floor, that MUST be caused by the hydraulics. The brake fluid is going SOMEwhere, and so if it's not leaking out of the system - it's moving within the system, to a void, likely an air pocket/air bubble.

When you do 'manual pump bleeding', are you doing it the 'right' way - the longest line (passenger rear) first for a pump or two, then the driver's side rear, then the passenger front, then the driver's front, then doing that until not even the tiniest air bubble comes out of any one line? Are you using clear hose to see the air bubbles come out? Are you bleeding into a container of brake fluid, however shallow, to block air going back up the line?

I'm still highly suspicious of the master cylinder, being it's the number one and usually only cause of a squishy pedal then going to the floor. If I had five reman/OE Motorcrafts go to the floor on me I'd look up aftermarket cylinders and see if one of them had a design that improved on the factory design, or what, if any, was the factory defect.

Have you looked up the part # to be sure what you're using is the correct part # for your vehicle? Many dealers will substitute parts and give you one that 'works' from an earlier or later year without having the slightest idea it would cause any issue.

Just looking at the Master Cylinder parts list for a 1995 Explorer on RockAuto shows that there are different master cylinders for models with/without cruise control and with/without a brake proportioning valve on the master cylinder. Perhaps the master cylinders you're using have been incorrect for your particular application, even if they would be 'correct' when going by the VIN, but that would assume a stock system, not modified in the way you have done.

 

[gmanpaint]

Thanks for covering the basics Anime.

The proper manual foot pump bleed sequence was done, multiple times. A power bleed and gravity bleed net the same results. I use clear hose going into clear plastic water bottles when bleeding. I also have a self feed gravity fluid bottle for the reservoir.

Being the system will pump up and hold a solid pressure with the engine off and loses pressure with engine on, im not convinced it is only hydro. It could be vacuum. Im staying open minded at this point on what the issue could be as I was positive on what the problem was in the past replacing parts only to have no changes.

The stock prop valve was located inside the abs hcu unit. The aftermarket valve simply replaced it.

The stock master part # is specific to the 95 by Motorcraft and is the same. This master is the one used by 1st gen owners who swap in a 2nd gen rear axle.

Since I can't find any signs of leakage anywhere, something mechanical must be the issue, this I agree. Losing pedal with engine on, is leading me to either the master bypassing internally, or the booster losing it's pressure. Booster could be defective.

In the black hole registry all the pics and details of the issue can be found documented along the way. It is about 10 pages worth spread throughout, starting about 2/3 thru.

 

[Anime]

If others have used the same 95 master on their 94s with the exact same setup, that's a clue it might work, but if you're using it on a 95 with different front calipers and a slightly different system, there's room for problems.

The only thing the master cyl with cruise probably has is a plug for the connector to disengage the cruise when the pedal is pressed, but the right master with/without the proportioning valve in the master might be the key. If you've got two proportioning valves in the system, one in the master, one in-line going to the rear, that might be the issue. If you've got just the in-line proportioning valve, it might not be a 70-30 split, but rather the rear brakes are just getting limited and the fronts are getting full pressure. Maybe the master isn't up to this and without a 4-way proportioning system the master gets bypassed.

Generally I'd just say get an aftermarket master cylinder and booster and see if that works. If the same thing happens, something is screwed up in the system downstream that is causing the master to fail or be bypassed. Calipers, lines/connections, or the in-line valve.

Oh, and whatever you do, no single-flaring on the connections. That's asking for leaks and it's unsafe on something as critical as a braking system.

 

[gmanpaint]

Just for giggles, I did as Jon asked with the booster.

Ran the engine, pumped the pedal, and turned it off. Pulled the one way valve and got a nice audible from air on the booster.

To make sure I have good vac on the line I started it again, and placed my finger over the valve. It about sucked my finger into the opening. All good there.

So as much as I hate to do it, im going for another master. Orielys is selling a new brand I haven't tried yet so we shall see what happens.

 

[turboexplorer]

One more thing to try that has helped find issues at my work. First get 4 vise grips and some rags. Pinch off each line on the flexible lines going to calipers. Start engine and pump up brakes. Should be nice and hard. If no issues the your master, booster and lines are okay. Remove one vise grip at a time. Test lots on each one you remove since you mentioned its intermitant. When it fails you will know if it's a specific corner causing the issue. Believe it or not we have had several cars with crappy calipers or ill fitting pads have similar issues. If you can eliminate it down to before the pinch off or after you will be narrowed down to a section. Then go from there. Super cheap test that I haven't heard mentioned yet.

Edit: Think I fixed most of my spelling errors, typing on a phone. Also apologize I tried to post the test yesterday on the black hole thread but I haven't renewed my elite membership yet so wouldn't let me and inbox is full.

Also hope it goes without saying but when all the lines are pinched off DO NOT attempt to drive the truck. You have essentially disabled all the calipers.

 

[gmanpaint]

One more thing to try that has helped fin issues at my work. First get 4 vise grips.vand some rags. Pint he off each line on the flexible lines going to calipers. Star engine and pump up. Should be nice an hard. If no issues the your master booster and lines are okay. Remove one vise grip at a time. Test lots on each one you remove since you mentioned its intermitant. When it falls you will know if it's a specific corner causing the issue. Believe it or not had several cars with crappy calipers or ill fitting pads have similar issues. If you can eliminate it down to before the pintch off or after you will be narrowed down to a section. Then go from there. Super cheap test I haven't heard mentioned yet.

Now thats an awesome tip I haven't heard! I think I only have 3 vise grips but I have a couple C clamps that might work the same.

Thanks! I will do this as soon as I can and report my findings before I go and spend more $$ on another master.

 

[gmanpaint]

Had a few mins to try the pinch test. Pinched them all, and it seems the pedal pumped up better. With engine off it will get so stiff, it can't move at all, but keeping the pressure on the pedal and starting the engine, the pedal loosens up and depresses. Ok, that's normal.

Removed the rears, pass side first than dr side. It's hard to tell which, but the pedal loses pressure with them removed.

Pinched the rears again, and removed the fronts. Pass side, than dr side. No pedal change, and seems to hold pressure.

So I did a little test. I turned down the rear pressure on the valve, pinched off the rears only, and took it around the block. Only had front brakes, but pedal held pressure and no bypass with pedal to the floor.

So...... It's either one of the new rear calipers, or the prop valve was turned too high. I set it at 500 psi as everything I read said that would give me 70/30. The gauge could be off on it.

As soon as I get somebody over I can get a reading on the gauge to are where it's at now.

Sounds like progress to me, and am optimistic the valve is the culprit in all this. I have been wrong before (many times) so we shall see.

 

[Bobmbx]

Sounds like progress to me, and am optimistic the valve is the culprit in all this. I have been wrong before (many times) so we shall see.

Yay! Its always a good feeling when you're easter egging a problem and you can change to result. At least you get more clues to work with.

And its always the simple things. Always.

 

[AlexSport'00]

Hopefully it's as simple as a bad caliper! Not sure why that would cause pressure drop only when the engine is on though...

 

[rizzjc]

But how could one bad caliper cause the whole system to fail, when it's not making fluid? It's not like there is a bypass in the caliper where it could send fluid somewhere else.

 

[swshawaii]

Ditto. How can a caliper cause a pressure drop if it's not leaking?

 

[gmanpaint]

Well the back pressure could be too much for the seals inside the master, and caused it to bypass.

The calipers are all pretty new still, but im thinking the prop valve is to blame. This unit was not a cheap one by any means either. Will mess with it some more tomorrow.

 

[swshawaii]

Obvious question not asked, especially with the EF gurus here. Are ALL the brake bleeders on top after replacing the calipers?

 

[gmanpaint]

Obvious question not asked, especially with the EF gurus here. Are ALL the brake bleeders on top after replacing the calipers?

Thats a great question, and one I faced a couple years ago. I had a bleeder break on a rear caliper while working on it once. The friend I was visiting at the time had a spare caliper we swapped it out with. Turns out it was for the other side and the bleeder was on the bottom. I replaced it with a new one later on.

So for those that don't know, the bleeders should be on top to allow air out, and not trap bubbles. On a gravity bleed, you can remove the caliper and turn it over to allow air out if needed.

 

[turboexplorer]

To be completely honest I have no idea "how" it can do it. All I know is sometimes they do. Weird I know, I am a manager and full time auto tech at a big shop and I can't explain it. But know that it has happened several times in recent experiences. In fact least month I think, my have been longer. We had a Mercedes C300 that was doing the same thing. Wouldn't completely loose brakes and go 100% to the floor but would go 85% or so. Enough to make you grab a little seat fabric with your rear each time it did though. And did the pinch test and sure enough found the left front caliper doing it. Replaced it and never saw the issue again. And it was completely random when it would do it as well. :scratch:

Like he said though, with no vacuum assist it should get rock hard like it won't even budge, when engine started it should fall a little. That is normal and shows that both the master and the booster are working. Also eliminates the cracked/flexing firewall possibility. (Not very common) You can then pinpoint it down to front or rear and even a corner from there. Easy test and has worked wonders for use when we have for lack of better words retarded brake issues. The same test can also tell you if there is an ABS accumulator or spring problem. This won't be on gmanpaint's because he has eliminated his, but food for thought with future people looking through this thread to find answers to issues.

So a bad caliper for whatever reason could be one answer. The other possibility I have seen is the pads get stuck and don't slide properly. You would think with that much pressure that the pad would get slide to the rotor regardless of fit and get stuck there and premature wear. Believe it or not have seen it twice this year where the pads wouldn't slide and end up flexing their packing. So as you press on the pedal it would flex and give you that soft pedal feel. And as you release the pedal the pad backing would press the piston back into the caliper. Remember before everyone says that's not possible is it takes a VERY small amount of free movement to cause an issue. For example we have all, I would guess, changed brakes at some point and how many full strokes of the pedal do you do before you pump the brakes back tight after you have changed the pads? A bunch and there isn't a whole tone of free room when you put fresh pads in. Also on that pad front. If you have say a pad that has a formed bump or nipple type thing on them for alignment reasons or whatnot, if that is in the wrong spot (like piston sitting on it) it can cause a similar retarded flexing problem. If you think pads can't flex, then you haven't read into part of the reason the High Performance stuff uses fixed calipers and multiple piston's.

Either way I think we have narrowed gmanpaint's issue down a bit. With what he said I would attack the rear and find the issue, and lets go from this :roll: to this :exporange. Even though its all fresh parts within a year or so doesn't mean there isn't a really goofy issue.

Super happy you made some progress, sorry to jack the thread with a bunch of my goofy experiences but figure with your issues this thread may see a bunch of people looking for future answers to problems so hope others can use my experiences to help them as well.

Keep us updated on progress and what you find!

 

[turboexplorer]

Also more food for thought, I am now solid axled as most know and I eliminated my ABS pump as well. But I don't run a portioning valve at all. My brakes are fantastic, been super happy. I think that stic-o also doesn't run one if i remember right, or njss2 when he did his and had no issues. On loose gravel or in sand my front lock just before my rears. Perfect for my set up, never get happy on the rear end but at the same time its right there just locking up after the front giving all 4 tires good braking. Then when in 4WD of course they are all locked together through the drivetrain so all 4 skid at the same time.

 

[gmanpaint]

Thanks a bunch to turboexplorer and his hands on experience. That is part of why the payscale is where it is with trades, we not only pay for labor, but knowledge and experience. I really appreciate your sharing some of that here with all of us.

I have learned more about brakes in the last couple of years than I have in my past thats for sure. The harder the problem, the more I learn, and the more I retain it all. Really wish I didn't know as much as I do to be honest. LOL!

If the calipers turn out alright, and the prop valve can't be fine tuned correctly, I will just delete it entirely now that I know a couple of you have not used one.

Thanks again. :biggthump

 

[turboexplorer]

Anytime!!!

 

[delexploder]

You really should replace your soft lines, while I agree with the function of this pinch test pinching those lines will cause line failure ,letting a caliper hang from its line will cause line failure, and for that matter line failure could be your problem, the soft lines break internally and act like a check valve, I cant tell you how many times I have found this on customers cars, time and old nasty fluid can cause it also but most of the time it has been obvious that the line was pinched, as yours seems to be in the rear it could also be the soft line from frame to axle ( pos stretched?) But whatever it turns out to be I would change the soft lines

 

[swshawaii]

Work done to correct the issue:
1) Replaced Master cylinder. Three times. All failed and bypassed just as the original issue.
2) ABS Delete mod.
3) New 3/16" hard lines installed except the line in the frame rail.
4) New power booster installed and Motorcraft Master cylinder (#4) at same time.
5) New calipers & pads.
6) New soft lines.