The Black Hole

[GRNMACHINE]

I should have been more specific! I was searching for the virgin lynchy threw in the hole. You dont come across those too often here in the States!

And thats a fried PB & Banana samich! TCB man!

 

[gmanpaint]

I should have been more specific! I was searching for the virgin lynchy threw in the hole. You dont come across those too often here in the States!

Trust me, if there is a virgin in the Black hole, she ain't no more, your searching is useless

Heh heh heh!

 

[lynchy wa]

I dont want to get in trouble....But...If you come across her is she technically still a virgin?

 

[gmanpaint]

Actually that all depends on how you go about that, and...................WAIT A MIN!

:


Lets get back on top(ic) here and say Whoa! (as in brakes)

Where was I? Crap Lynchy, you got me all messed up now, I lost my train of thought. :scratch:

Stay tuned to another post about how the Black Hole, can devour one mans wallet at light speed.

 

[gmanpaint]

I think that maybe that virgin lied.

After 2 tries at bleeding the system with the engine running, there is still a soft failing pedal.


1st bleed:
Pass rear, Dr rear, pass front, Dr front, in that order. Pumped and held, bleeder opened, done 3-4 times per caliper, until no bubbles were present. Rears bleed great, and have a nice firm pedal. Lost the firm pedal after the bleeder was opened on the pass front & bled.
No air bubbles to be seen after all 4 are bled, and a failing soft, spongy, pedal almost to the floor.

2nd bleed:
Same as above & same exact results.

I am getting air in the system somehow. I looked over all possible connections for leaks and found none. Weird thing is when the bleed is done with engine off, it will get a nice firm pedal, but once the engine is ran, the pedal fails.

Could the power booster diaphragm be bad, and letting air in somehow? I know that a master can go bad, and leak fluids into the drum, but can it also force air into the master?

I am at a loss. I have done everything that I personally know how to do with brakes. I guess I will have to take it in to a shop, and let them bend me over and "Maybe" fix it.

 

[GRNMACHINE]

You have already gone way beyond my knowledge of brakes! A long time ago! You have replaced pretty much anything and everything I can think of.

I hate to think you are going to drive it in for service and become the sacrificial virgin next....

Avoid the Brake Offices of Ben Dover & C. Howett-Fields by all means.

And seriously good luck, I Was going to say it has to be something really simple but that thought went out the window ages ago.

 

[CDW6212R]

Yes, you have done about everything that can be done.

Did you bench bleed the master cylinder really well before making the final line connections? That's a basic step to avoid having too much air at the head(pump(master cylinder)). Next, how did the small pin fit into the booster and master cylinder? There is a proper clearance for the pin to fit inside the MC, I'm not familiar with any specs or where to hunt those.

If that's all correct, then all that should be left is the ABS pump if the vehicle had one. You removed that already yes? The ABS pump needs a special diagnostic tool to bleed it when enough air gets into it.

Lastly, did every one of the bleed screws function well, and plenty of fluid was pumping out of each of them? From what I think I've read of your brake changes, I'd go back to the MC and booster installation, the bleeding and pin depth. That's as much as I know, I usually never get big issues to have to work on the big stuff. Keep at it.

 

[lynchy wa]

I've seen a split diaphram on a scout having similar issues.
I'm off to resign my position of "High priest of wacky dacky doo dah" seeing as my spell didnt work, bugger!!!

You might need a REAL priest mate!

 

[gmanpaint]

Each Master was bench bled before install until no bubbles were present.

The rod on the booster has never been touched. I know all to well about how it can be adjusted in/out for the bore stroke.

ABS HCU has been eliminated and a nice SBCC prop valve has been installed. Getting 500-600 PSI to the rears.

All new calipers and all new bleeders. They all work smooth.

I am going to gravity bleed it tomorrow for a few hours. If there is still air found after that, the booster is next to be replaced. I might even run new hard lines on this nightmare.

 

[zukman]

if it bleeds off when the engine is running the booster is crap can e say bigga vaccum leaky

 

[gmanpaint]

Zukman, So, since the rears keep a firm pedal but the fronts lose the pedal when the calipers are bled, does this mean that the booster is only used for the fronts? My understanding of the booster is that it just uses negative vac pressure to use the diaphragm inside to push the rod into the master cylinder.

I hear a hiss, like a vac leak, every time the pedal is pumped at the booster. I was concerned that it might be leaking. So, I went and got the retired auto mechanic neighbor over to get his opinion on it. He listened to it as the pedal was pumped, and said it was normal.

I have never stood at the booster area while the pedal was being pumped until today, and heard this. So I didn't know if this was normal or not.

 

[turboexplorer]

That is normal from the booster. There is a atmospheric valve on one side of the booster diaphragm and vacuum on the other. The lack of pressure on one side lets the atmospheric pressure push on the diaphragm. Its the air pressure that does the boost work not the vacuum sucking on the diaphragm if that makes sense.

The sound is just air entering and leaving the booster. That is normal and does it every time you apply the brakes. Under normal conditions there isn't a ton of air that moves (Firm pedal = minimal movement) therefore can't hear it plus usually have truck running radio etc.

Second thing is the booster will have NOTHING to do with the pedal going to the floor that I have ever heard of. It helps you push the pedal. If it was bad and the diaphragm was split or cracked for one would have any power brakes and you have never complained about that that I have heard you say and second you would hear the vacuum leak inside the truck.

When the diaphragm is emptied of all it vacuum the booster more or less acts as if it isn't even there. It is then just a straight mechanical connection between the pedal and the master. All there is is a rod that goes between the two. The diaphragm hooks in the middle of this rod and is where it helps push it towards the master.

I know you have checked it but there are a few simple tests you can do.

First: Don't run the rig while bleeding the brakes.
Second: Don't let the pedal go all the way to the floor while bleeding. Have the person inside the truck press the pedal you crack the bleeder slightly to let fluid out as normal but close it back up while the fluid is STILL flowing. This will make sure that there is no air getting sucked up in. I have seen more than several cars that had this issue even though the pedal went to the floor and wasn't moved they would always suck air in. So close the bleeder while the fluid is flowing that way you can guarantee that no air could go back in since the fluid is still coming out.
Third: Double check all pads on the truck. Make sure that the outer pads an all corners are flat against the caliper and that the inside pads on all corners are flat against the pistons. I have seen where some have put some springs in wrong or has two silencer plates instead of one or caliper isn't sitting at 90* to the rotor etc. All these things can push the pistons back in there bores and the fluid back to the master leaving you with a soft pedal since the first part of your pedal is used just to take up the slack that any of these problems may have made.
Fourth: After you have bled the brakes start the truck and see if there is the red brake light on on the dash BEFORE you ever touch the brakes after the bleeding process. Two things cause that light the e brake and the pressure differential switch that is in the master. If for some reason the pressure differential switch inside the master is being flipped it blocks off the other circuit which would give you a soft pedal. It does this in case one circuit fails it blocks it off to help prevent all the fluid from exiting the bad circuit. It is a safety feature and it can sometimes be switched while bleeding the brakes. (It thinks there is a leak which there is since you are bleeding it) Not common but if you I can tell you how after bleeding to switch it back.
Fifth: Check very close to all mounts on the firewall. Make sure the pedal is firmly attached and that NO movement of the firewall is present when standing on the brakes. So older rigs had issues with the firewalls cracking and it would allow for flew and would feel like a soft pedal. Never heard a second gen doing this but its worth a good check.
Sixth: Check all rubber lines with someone depressing the releasing the pedal. Make sure that none are expanding from the pressure. I have seen a few where they would balloon so to speak when pressure would be applied. Weird, but the ones I have seen do this weren't even consistent. You would think that if it had a soft spot they would expand every time the pedal was pushed but that wasn't the case, weird.
Seventh: You can get gauges that you can put in line at each caliper connection and you can see the exact hydraulic pressure being applied to each caliper then when the pedal goes soft you can see which circuit has low pressure etc. Expensive and most don't have access to these gauges but all dealers should. Bummer means taking it to a shop.
Eighth: Check every rotors run out while ON the truck. If any are wobbling it will push the pads back into there bores causing a soft pedal. But if it does it just sitting there that wouldn't be an issue.

I am A.S.E certified in 7 of the 8 areas brakes being one and that is a few things I have seen that are "not normal" so to speak. I'm trying to think of things that may be an issue you haven't checked yet but I'm sure you have. We have all thought about this issue dozens of times. Those are a few I have seen in the field as weird very hard to find issues. This problem has been the plague for you. Try some of those if you haven't and really bottom line if no issue is found is to use those brake gauges so you can see exact pressure and you can then eliminate one circuit then down to component etc. But since its all been replaced its to hard to say.

Best of luck let me know what you tried or find.

 

[gmanpaint]

Thank you for all that sir

I will try the bleeding again using the pedal instructions. Since I had good pedal after bleeding with engine off, only to lose that pedal after the engine was started, I thought that maybe, it needed to be running when bleeding this vehicle.

Since the ABS is gone, wont a good old fashioned gravity bleed be just as good as a power bleed or a conventional pump bleed procedure?

I always close the bleeder when the fluids are still flowing out, and I use a tube & recovery bottle, making sure the tube is in the fluids as to not suck air back in. I watched all the rubber lines as it was being pumped, all good, and they are new to boot. .

I have never seen the red light come on in the dash yet, even after the pedal bypassed.

Pads are new and good, including the new E=brake hardware and shoes.

My booster drum does move when the pedal is being pumped. I thought that to be normal as well....no?

 

[CDW6212R]

That is normal from the booster. There is a atmospheric valve on one side of the booster diaphragm and vacuum on the other. The lack of pressure on one side lets the atmospheric pressure push on the diaphragm. Its the air pressure that does the boost work not the vacuum sucking on the diaphragm if that makes sense.

The sound is just air entering and leaving the booster. That is normal and does it every time you apply the brakes. Under normal conditions there isn't a ton of air that moves (Firm pedal = minimal movement) therefore can't hear it plus usually have truck running radio etc.

Second thing is the booster will have NOTHING to do with the pedal going to the floor that I have ever heard of. It helps you push the pedal. If it was bad and the diaphragm was split or cracked for one would have any power brakes and you have never complained about that that I have heard you say and second you would hear the vacuum leak inside the truck.

When the diaphragm is emptied of all it vacuum the booster more or less acts as if it isn't even there. It is then just a straight mechanical connection between the pedal and the master. All there is is a rod that goes between the two. The diaphragm hooks in the middle of this rod and is where it helps push it towards the master.

I know you have checked it but there are a few simple tests you can do.

First: Don't run the rig while bleeding the brakes.
Second: Don't let the pedal go all the way to the floor while bleeding. Have the person inside the truck press the pedal you crack the bleeder slightly to let fluid out as normal but close it back up while the fluid is STILL flowing. This will make sure that there is no air getting sucked up in. I have seen more than several cars that had this issue even though the pedal went to the floor and wasn't moved they would always suck air in. So close the bleeder while the fluid is flowing that way you can guarantee that no air could go back in since the fluid is still coming out.
Third: Double check all pads on the truck. Make sure that the outer pads an all corners are flat against the caliper and that the inside pads on all corners are flat against the pistons. I have seen where some have put some springs in wrong or has two silencer plates instead of one or caliper isn't sitting at 90* to the rotor etc. All these things can push the pistons back in there bores and the fluid back to the master leaving you with a soft pedal since the first part of your pedal is used just to take up the slack that any of these problems may have made.
Fourth: After you have bled the brakes start the truck and see if there is the red brake light on on the dash BEFORE you ever touch the brakes after the bleeding process. Two things cause that light the e brake and the pressure differential switch that is in the master. If for some reason the pressure differential switch inside the master is being flipped it blocks off the other circuit which would give you a soft pedal. It does this in case one circuit fails it blocks it off to help prevent all the fluid from exiting the bad circuit. It is a safety feature and it can sometimes be switched while bleeding the brakes. (It thinks there is a leak which there is since you are bleeding it) Not common but if you I can tell you how after bleeding to switch it back.
Fifth: Check very close to all mounts on the firewall. Make sure the pedal is firmly attached and that NO movement of the firewall is present when standing on the brakes. So older rigs had issues with the firewalls cracking and it would allow for flew and would feel like a soft pedal. Never heard a second gen doing this but its worth a good check.
Sixth: Check all rubber lines with someone depressing the releasing the pedal. Make sure that none are expanding from the pressure. I have seen a few where they would balloon so to speak when pressure would be applied. Weird, but the ones I have seen do this weren't even consistent. You would think that if it had a soft spot they would expand every time the pedal was pushed but that wasn't the case, weird.
Seventh: You can get gauges that you can put in line at each caliper connection and you can see the exact hydraulic pressure being applied to each caliper then when the pedal goes soft you can see which circuit has low pressure etc. Expensive and most don't have access to these gauges but all dealers should. Bummer means taking it to a shop.
Eighth: Check every rotors run out while ON the truck. If any are wobbling it will push the pads back into there bores causing a soft pedal. But if it does it just sitting there that wouldn't be an issue.

I am A.S.E certified in 7 of the 8 areas brakes being one and that is a few things I have seen that are "not normal" so to speak. I'm trying to think of things that may be an issue you haven't checked yet but I'm sure you have. We have all thought about this issue dozens of times. Those are a few I have seen in the field as weird very hard to find issues. This problem has been the plague for you. Try some of those if you haven't and really bottom line if no issue is found is to use those brake gauges so you can see exact pressure and you can then eliminate one circuit then down to component etc. But since its all been replaced its to hard to say.

Best of luck let me know what you tried or find.

That's a very good list of checks. I think the 2nd one and the firewall strength are the most likely for Greg's truck. It is really common to have air get back in when the brakes are bled, just before closing the screw. Only crack the bleed screw enough to let pressure push fluid out.

I wonder how much force it would take to affect the firewall and lead to booster movement.

I bought a pressure bleed system from Modine two years ago. Those are excellent to bleed brakes, and it only takes one person with that. I've only used it twice, for my two SUV's. It made for a 15 minute job by myself, slick. Those kits start at around $70 IIRC.

 

[turboexplorer]

Thank you for all that sir

I will try the bleeding again using the pedal instructions. Since I had good pedal after bleeding with engine off, only to lose that pedal after the engine was started, I thought that maybe, it needed to be running when bleeding this vehicle.

Since the ABS is gone, wont a good old fashioned gravity bleed be just as good as a power bleed or a conventional pump bleed procedure?

I always close the bleeder when the fluids are still flowing out, and I use a tube & recovery bottle, making sure the tube is in the fluids as to not suck air back in. I watched all the rubber lines as it was being pumped, all good, and they are new to boot. .

I have never seen the red light come on in the dash yet, even after the pedal bypassed.

Pads are new and good, including the new E=brake hardware and shoes.


My booster drum does move when the pedal is being pumped. I thought that to be normal as well....no?

No the master and booster shouldn't move at all. They are fixed to the firewall and shouldn't move. Maybe a few thousands or so just from the pressure but shouldn't really be visible with just watching it. If it defiantly moves then I would start checking there. Would be a pain but may be worth pulling the booster to inspect mounting and firewall.

Its about the only reason left for your issue since every component has been removed or replaced.

 

[gmanpaint]

I will try to get a video posted of how much the booster/master moves when pumping the pedal. It def moves more than a few thousandths.

I don't really understand how it moving affects the brake pressure if it is all sealed up tho. :scratch:

 

[turboexplorer]

Think of your pedal as a lever. Say it has a ratio of 7:1. So now if your booster moves say 1/8" your pedal where you push through the 7:1 ratio now moves 7/8". So any movement at the firewall gets very exaggerated by the time it gets to your foot. They use rhat pedal ratio to create mechanical advantage. Hence hw we can stop a 5000lb rig with minimal use of 1 single foot. First through mechanical advantage next from the help of the booster and finally hydrolic advantage.

All this only works in a closed system. Including the mechanical pedal. Think of a teter toter. When it is even side to side and say there is 100lb on the other side you push with 100lbs it will move. IF it has a solid pivot point. It wont move until that 100lbs of pressure is reached. Now say we put a 2" thick rubber bushing as a pivot instead of a solid point. Now when you apply pressure the pedal so to speak or the other side you are pushing on moves but it does not lift the other side. So if you apply it to your truck. Pedal moves moves firewall but is not moving the rod to the master.

Hope that made sense.

Send via Android

 

[gmanpaint]

Quick video from multiple angles to try to show the movement of the booster while the spongy pedal is being pumped. Mind you, not that much force being applied to the pedal as my helper is a munchkin

 

[turboexplorer]

That is a lot! Really is if you consider a member of the lolly pop guild is pushing on the pedal. Thats to much. I would pull the booster and Very carefully examine the firewall and booster bolts/studs as first priority then if needed can continue chasing the issue if one even still exists.

Sent via Android

 

[gmanpaint]

UGH!

My back is going to hate me removing that thing.

Will get to it as soon as I can tho. I do have some 1/8" plate to reinforce that firewall if need be.

Nothing has ever been easy on this rig, why would this be the exception? LOL