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

[gmanpaint]

Well, as you can tell I am a little upset over the ongoing brake issue that has haunted this rig for a couple years now and has left it sitting more than it should be. I will state what the issue is, what has been done so far, and what has been done again. Any insight no matter how small or big is welcome, and I will do my best to keep an open mind on what your thinking.

The rig: 1995 Explorer XLT 4wd w/cruise


Main issue (started 2 years ago): Soft pedal & intermittent pedal pressure loss.

Symptoms: The pedal has been soft when operating it, and every now & than the pedal loses all pressure and drops to the floor causing no brakes at all. The pedal will pump back up again when this happens after a few seconds, and work again.

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.


No leaks fluid or air to be found in the system, and checked by myself, friends and eventually a brake shop. Brake shop said master bypassing is all they can figure what was wrong. Replaced master again with another Motorcraft (#5), same issue happens.

Power bleeding, gravity bleeding & manual pump bleeding have all been done to try to get a firm pedal, with no luck.

Just recently replaced the junction tee and all 3 flare nuts with new flares made to make sure that wasn't the issue. Nope, still the same issue.

Today after another gravity bleed and a quart of new fluid flushed through the system, the following happens:

Engine off: Pedal pumps firm & holds perfectly.
Engine on: Pedal drops to the floor and wont pump back up.
Turn engine off: Pedal pumps right back up and holds pressure perfectly.
Restart engine: Pedal fails and drops to floor again and wont pump back up.

Checked for leaks, none to be found.

So I have done everything I can think of, and others have tried as well to offer suggestions in the rigs registry, but I thought to get a larger audience by making this thread and hear some others opinions on this issue.

I'm seriously at my wits end and am VERY serious about scrapping the rig if this can't be solved. Thank you in advance for any thoughts on how to fix this. I will answer any questions when I come back to check on this thread as I sneak time away from work or what not.

 

[Bobmbx]

Try adjusting your master cylinder push rod.

 

[BobWiersema]

Wow! Thats a good run of bad luck. Sounds like you replaced everything.
My only question is about the ABS. No connections to that at all?

 

[gmanpaint]

Thanks guys.

The booster itself was replaced and thats where the pushrod is located, same issue with both.

Bob, the entire unit was removed, pump and all. A SSBC prop valve unit was installed for the rear lines located next to the master and a solid mount made for it for zero movement.

 

[Turdle]

I believe you've been thrown into a bad run of master cylinders.

It has to be that, you've gone over everything.

If you do not have fluid leaking or air in the lines the MC is not pumping solid pressure.

 

[Bobmbx]

Wow. Brake systems are intentionally simple in design, so there aren't a whole of things that can go wrong. You've replaced all the complex components with no change, so I'd stop doing that.

This may sound weird, but its the only thing left in the system that moves. Check your disc thickness. If someone has put a different disc on, say a two-disc vented to a single disc, you'll lose quote a bit of distance and will have to push your pistons out a lot farther. I'm thinking at least one piston is all the way out and isn't forcing the pad onto the rotor (which is what causes the resistance in the pedal).

Do you have brakes when the engine is off and the pedal is firm?

 

[gmanpaint]

Dunno Jon, 5 in a row?

Forgot to mention the discs were all replaced along with E-brake kit.

As mentioned, engine off- firm pedal. Engine on, no pedal.

Guess the replacement booster could be bad? I'm so sick of throwing $ at these brakes, it's not funny.

 

[Turdle]

Yes firm brakes with engine off. Will they stop the truck with the engine off?

Do the brakes "work"? in other words. Not just pad movement.

 

[gmanpaint]

I imagine they would as the pedal is firm as it gets when engine off. I'm not about to test that out on the road. I can roll it in the drive, and they would work I believe. I can hold with pressure forever on the pedal and it won't creep Down, or lose pressure.

 

[Bobmbx]

I imagine they would as the pedal is firm as it gets when engine off. I'm not about to test that out on the road. I can roll it in the drive, and they would work I believe. I can hold with pressure forever on the pedal and it won't creep Down, or lose pressure.

Are you certain the booster is holding a vacuum?

 

[rizzjc]

I don't know a lot about how the system works in detail, but what about some electrical issue, since it only fails when the engine is running? Some kind of crazy short or something that only shows up when it's running? Maybe a stretch, but really odd problems with no obvious solution can often be some phantom electrical issue.

 

[Turdle]

Have you ever had an engine die while moving and felt the lack of brakes? It's pretty weird to say the least. The vacuum assist merely overcomes that effort. It would be nice to know if the brakes will work with no assist. Try this moving back into the driveway--just have your e brake ready. Get the truck moving, and shut it off. Now apply the brakes to stop. The emergency brake will stop you at that speed.

 

[Turdle]

Are you certain the booster is holding a vacuum?

With the engine off ( right after running), pull the plug out of the brake booster and you should hear a suction noise.

 

[gmanpaint]

The one way valve is working or it wouldn't pump up at all.

I will have a go at it in the morning. It's a manual so I can go slow and have it in the opposite gear it's moving to help slow it down if needed. E-brake cable isn't working that well from slack in it. I can start it back up on a roll if needed

 

[Anime]

I'd agree that it's not a bad run of master cylinders, rather, I'd guess the masters are being bypassed due to some flaw in the system design or a component that is holding pressure, and the masters are a weaker link.

I also don't think the system should "work" without the engine running/having been run to generate vacuum. You don't generally install a booster and put a brake system together and suddenly have vacuum to stop the vehicle with. You have to run the engine and drive for awhile for the vacuum to build up. There might be enough hydraulic pressure to make the pads contact the rotors some and stop the vehicle when pushed by hand, but that's not anything close to an operating system.

I would think you should go backwards and try to remember what worked when before you got the system in this state. Was the ABS removed prior to the system having any issues? Did the system still work flawlessly without the ABS? Was the SSBS valve unit installed prior to the system issues? Etc. If you changed a ton of things at once and redid the system, it'll be harder to isolate the single cause (if there is just one), but you may just have to start fresh and check everything in the system 20 times to be sure you're not overlooking something.

Were the new calipers on there before these issues? Did you check them prior to installation? They may be cheapos that were rebuilt incorrectly or have sat and so are seized and you're blowing master cylinders trying to get seized caliper pistons to move past a point they won't - without more pressure than the system is made to generate.

I'd agree the original issue sounds like a master cylinder going bad, but the system not working now might be a new cause and unrelated to the original problem. You might also now have two problems if there is an issue with the master cylinders you've had. Are you SURE each of the five Motorcraft master cyl's were all different and you didn't get them from a dealer that kept swapping out the same two bad ones?

Scrapping the rig would be a shame and an overreaction. Even if you have to redo everything with aftermarket parts with new calipers, a booster, master, and maybe even another valve and redoing the lines and connections, it may be a lot of work but it might just be you've got some defective stuff on the system. Just because it's Motorcraft doesn't mean it works perfect out of the box.

 

[gmanpaint]

I think Jon asked if they worked just to see if the calipers were actually doing their job is all.

Joe, I removed all electrical components when the ABS delete was done. This is a straight forward mechanical/hydraulic/vacuum system now. I do understand your thinking tho, as I have fought electrical gremlins in the past.

This started a couple years ago, and I did one thing at a time for the most part as time progressed. Master cylinder R&R a couple times, then the booster, then the ABS delete mod with new lines, then new calipers, discs & pads, another master, and so on...This work all but stopped a year ago, and the rig has sat for the most part, but it did go on a wheeling meet last winter and the pedal only dropped to the floor a couple times. Both times were not in a situation that was dangerous either. This was a random occurrence after all the work was done, but this rig stopped getting DD use years ago. After sitting for the last 8 months or so, the pedal now drops a lot, and creeps to the floor while holding it with good pressure.

A few days ago, it went in to get safety inspected (once a year) and brakes worked fine all the way there, with no issues, no pulling side to side, no rear lock ups, just normal. Anyways, the tech goes to bring it in the bay, and the brakes fail. Pedal goes to the floor on the guy as he is pulling it in the bay. He freaks and fails the rig on the spot. So he pulls it out of the bay, slams on the brakes multiple times in both directions, and they work just fine for him with no failure. He says the master must be bad on it to bypass as it did. So I ask him to hold the pedal down with it running, and sure enough, the pedal slowly goes to the floor, but that took an entire minute to happen and with him really pressing hard on the pedal. I take it home and the brakes work fine all the way. A little later on, I move the rig, and the pedal goes to the floor on me.

How's that for random, and frustrating as hell?

 

[R1dd1cK]

OK well I didn't see anything about bench bleeding the master before installing it. Did you bench bleed the master on a level surface with the ports capped with lines going back in to the master reservoir?

 

[gmanpaint]

Yes, yes I did.

I really appreciate all the ideas guys! Somebody is going to nail it sooner or later! :biggthump

The most obscure idea so far I have heard was from turboexplorer. He states the firewall is weakened and moves upon depressing the pedal and that wont allow it to pump up all the way. I didn't think this possible because it pumps up just fine with the engine off. I realize the booster does the work of a dozen men and amplifies the amount of pressure you put on it, but thats just it, with the booster working, you don't have to apply much pressure to the pedal, a big toe can work the brakes. :scratch:

 

[R1dd1cK]

Well I'm out of ideas.

 

[gmanpaint]

Anime, I just caught your edit.

The first 3 masters were cardon remans. The last 2 were motorcraft and the 4th being a used known working unit from another member.

Yes, a little drastic on my part for wanting to scrap the rig, but the frustration levels have surpassed any and all levels of my patience dealing with this matter.