Brake Booster Losing Pressure with Engine Running

[Brush Hog]

If it’s just a small weep at the fitting just tighten it a little more. Only takes about 1/16th of a turn or less. I had same problem called vendor and that was what they suggested. It worked.

 

[DirtDonk]

Back-and-forth a few times, getting tighter and tighter each time can work too, if just tightening it doesn’t.

 

[JeepGuy]

Yeah, was reading up a bit on the "Proper" way to get the flare to seat right. I guess my initial thought of loosen then tighten again was actually on the right path. I can't image there is enough wiggle room inside those fittings to completely screw up a new line, but who knows.

Time is running out unfortunately today, but tomorrow looks like I'll have time to go out and back out the fitting, inspect for damage to the end, then reseat it a few times. The leak is minor, but it is definitely there. Noticed it after cycling the pedal a ton of times.

Thanks for all the reply's.

 

[Apogee]

If push comes to shove, there are conical seat copper crush washers available for standard 3/16" and 1/4" tube sizes, and they can provide a degree of compliance between the seating surfaces to provide a good seal. They can be a little difficult to hold in place during assembly, but I'll typically use a little caliper assembly lube (basically jellied brake fluid) to stick them to the female fitting, then fit the tube and tube nut into the fitting.

 

[ksagis]

If push comes to shove, there are conical seat copper crush washers available for standard 3/16" and 1/4" tube sizes, and they can provide a degree of compliance between the seating surfaces to provide a good seal. They can be a little difficult to hold in place during assembly, but I'll typically use a little caliper assembly lube (basically jellied brake fluid) to stick them to the female fitting, then fit the tube and tube nut into the fitting.

I've used SECO 45 degree seals (100 degree included angle) in various areas but the smallest I've seen them is 1/4". Any idea of where one could source 3/16' variants?

Also, on NiCop lines, I'd swear that sometimes when I used either "increasing torque" or "loosen/tighten" approaches for a small leak that I actually made a small leak worse if I showered down too hard chasing the leak. I assumed that was due to NiCop line being so much softer than stainless that I ended up overdeforming the lines on the inverted flare (which doesn't really make sense to me). Any opinions on that theory and advice for torque amount for NiCop lines in terms of ft-lbs?

 

[JeepGuy]

Well, no news is usually good news, and in this case I have news. I've loosened and re-tightened these fittings several times to the point where a well seated wrench is beginning to spin off and round the fitting. At this point, all of the front stainless is coming out. I don't even really care if it is still usable, it will be gone across the front axle. I'll make and bend my own front lines and replace the long flexible front center line. At least that way, all of the leaking joints will be replaced.

Now onto the Banjo bolts at the calipers. On the last go around I noticed the passenger side banjo bolt was leaking, or I guess I should say the fitting is leaking. I either lost those along the way or they didn't come with the kit when I bought them. Either way, I had to source those out through Napa. I'm very tempted to replace those and the washer too from the vendor I bought the kit from just to eliminate any possibility of having the wrong ones installed.

On to the vacuum issues. So, I can get a pretty firm pedal with the engine off. As soon as I fire it up, the pedal goes to the floor with nothing about it being firm. Still don't know what is the cause of that. I disconnected the vacuum line and fired the engine. Firm pedal but still no braking power. The bronco is up on jack stands and the tires slow but never stop spinning. I've adjusted the rear drums to the point where the shoes drag and slow a spinning tire with no pedal applied.

As I type this, I have not found any issues with leaking lines at the MC, the Proportioning Valve, or any of the rear lines. I'm sure now that I have said that for certain there will be puddles somewhere on the rear tomorrow.

I'm really trying not to replace this brand new kit with anther brand new kit, but that seems to be my luck at the moment. Isn't this fun

 

[4xfun]

The small weeps in the system should not be causing the pedal to sink unless you can see a fluid when you press the brakes. They need to be fixed, but that may be a secondary issue.

Maybe I missed it, but did you pull the master cylinder, bench bleed it and test for resistance?
Check the proportioning valve part number to make sure that you have one set up for disk/drum installation and not disk/disk. That should not create the pedal issue, but you need the correct valve.
Did you fix all of vacuum leaks with your hoses?
Did you test the brake booster? Inspect the check valve and blow through it, then suck back. If you cannot get any air when you suck it is good. Hook up a vacuum pump and gauge to the booster, pump it up and see if it holds vacuum. If it will not pump up and hold vacuum the diaphragm is bad and you will need a new booster.
How much vacuum are you creating at idle? You may need a booster tank.

Nothing against the vendors, but new parts can sometimes be the issue.

 

[JeepGuy]

The small weeps in the system should not be causing the pedal to sink unless you can see a fluid when you press the brakes. They need to be fixed, but that may be a secondary issue.

Maybe I missed it, but did you pull the master cylinder, bench bleed it and test for resistance?
Check the proportioning valve part number to make sure that you have one set up for disk/drum installation and not disk/disk. That should not create the pedal issue, but you need the correct valve.
Did you fix all of vacuum leaks with your hoses?
Did you test the brake booster? Inspect the check valve and blow through it, then suck back. If you cannot get any air when you suck it is good. Hook up a vacuum pump and gauge to the booster, pump it up and see if it holds vacuum. If it will not pump up and hold vacuum the diaphragm is bad and you will need a new booster.
How much vacuum are you creating at idle? You may need a booster tank.

Nothing against the vendors, but new parts can sometimes be the issue.

Hello,

Yes, after multiple tries it is still obvious leaks with small puddles on the floor after sitting for awhile. When I tear it apart I'm going to inspect the front center brake line. My guess here is the hard lines did not ever seat properly and now that I've put too many ugguhh duguhhs on them they are shot. Just due to not having the replacement center line handy, I'll probably install all the lines and rebleed the system. If it still leaks at that joint, the center line will need to be replaced too.

I bled the master cylinder mounted on the vehicle. After a suggestion here I also plugged all four holes and tested it. It held pressure immediately and stopped the pedal from moving. I gravity bled this initially. I used the "one man" bottle at the wheel and pumped all of them for clear fluid in the line to the bottle. Then used a reverse bleeder extensively, going through an entire 32 oz bottle of brake fluid, with someone watching for bubbles and or overflow of fluid at the MC. I'll do the same process this time around but will probably just start at each wheel and avoid having to pull fluid from the MC. I guess there is always the possibility of air being trapped somewhere, but at this point I don't know where it would be.

I did not have a known vacuum leak with the hose from the bottom of carb to booster, and it does not appear to be leaking. I'm correcting the location of the vacuum for the booster with a new intake location. I probably should go by a vacuum pump with gauge.

The proportioning valve is the common Disc/Drum valve from WH and it was purchased along with the disc brake kit, master cylinder, lines, etc. The only thing I do not see in my pile of receipts is the actual brake booster, but it is new and either purchased from WH, BG, or T's OFRD. They are generally the only vendors I use due to locality (nothing negative at all against the other vendors on here).

All those years ago when I got this Bronco I redid every brake line and replaced the MC without a fraction of the issues I'm having now. That was on a cheap budget and cutting and bending all the lines myself. I was hoping getting this stuff all pre-bent would have garnished better results.

 

[4xfun]

Thanks for the clarification. It sounds like you confirmed that the booster and master cylinder are not the issue. I realize that I misread the post about the vacuum line routing. It sucks that the issue is with what you hoped was an upgrade to a better system and parts.

 

[Apogee]

I've used SECO 45 degree seals (100 degree included angle) in various areas but the smallest I've seen them is 1/4". Any idea of where one could source 3/16' variants?

Also, on NiCop lines, I'd swear that sometimes when I used either "increasing torque" or "loosen/tighten" approaches for a small leak that I actually made a small leak worse if I showered down too hard chasing the leak. I assumed that was due to NiCop line being so much softer than stainless that I ended up overdeforming the lines on the inverted flare (which doesn't really make sense to me). Any opinions on that theory and advice for torque amount for NiCop lines in terms of ft-lbs?

I get my conical crush washers from Crown Performance in Vista, CA, and keep some on hand for emergencies. As for the Ni-Copp tubing, I've found that I slightly reduce the stick-thru length on the die when forming flares to prevent buckling the tube above the flare, and that way I don't end up with any concentricity issues on the flare either. I've found that the assembly torques with Ni-Copp tend to be somewhat lower than with stainless or steel, and getting heavy handed with them can damage the flares like you describe.

To the OP, the fact that the MC hydraulically locks after ~1/8" of travel (basically enough travel for the internal cup seals to cover the ports between the bore and reservoirs(s)) when all of the outlet ports are plugged is a good sign that the MC is functioning correctly. That said, it begs the question as to where all that fluid is going when you apply the brakes with the engine running and and pedal is going to or near the floor. That fluid has to go somewhere, and whether the booster is functioning properly or not, a failed booster will 99% of the time create a higher/firmer pedal, not a lower/softer pedal. When you connected the front and rear brake circuits back to the MC, did you do them at the same time or sequentially, bleeding each respective circuit after it being added? This can tell you whether the issue is front or rear and can narrow things down a bit in my experience, though I use it more often to diagnose back rear parking brake calipers than anything else, but you have rear drums.

Which front disc brake swap is this? Chevy or Ford? If Chevy, do you have adequate knuckle clearance for the calipers to slide properly? Keep at it and you'll get there eventually. There are truly only so many things it can be in a brake system, as they're not all that complicated, it's just a matter of being methodical and using the process of elimination to rule things out until it can only be whatever it is causing the issue, and that's not always just one thing.

Tobin

 

[JeepGuy]

Front stainless is out, and new brake lines are made and ready to go in. Just waiting on the new center (frame to diff) line to show up.

@Apogee

My thoughts are the same as yours... Where is the fluid going? The last go around had pretty big puddles under the center section of the front diff. That is why I just decided to take it all out. Regarding fluid and the MC, the only well that is going doing down was the one for the front brakes. Rear brake well has maintained it's level of fluid and as of this post after a ton of brake cycling there is no visible fluid

I plan on separating the MC from the Booster again and checking the depth of the rod/plunger again, but other then that, those two pieces seem to be functioning properly.

I'm hoping the leaking center joint was the main issue and that will all be replaced shortly.

The Kit was all together for a Bronco Dana 30 or 44. I have the 44. There does not appear to be any clearance issues with the calipers.

 

[ksagis]

I get my conical crush washers from Crown Performance in Vista, CA, and keep some on hand for emergencies. As for the Ni-Copp tubing, I've found that I slightly reduce the stick-thru length on the die when forming flares to prevent buckling the tube above the flare, and that way I don't end up with any concentricity issues on the flare either. I've found that the assembly torques with Ni-Copp tend to be somewhat lower than with stainless or steel, and getting heavy handed with them can damage the flares like you describe

Thanks for vendor tip and for the sanity check on my theory, much appreciated!

 

[ksagis]

@JeepGuy, want to cross off what seem obvious but don’t think has come up yet.

On some disk conversions, one can install calipers on the wrong side. What’s the orientation of your bleeder screws? Post a pic if possible.

 

[JeepGuy]

@JeepGuy, want to cross off what seem obvious but don’t think has come up yet.

On some disk conversions, one can install calipers on the wrong side. What’s the orientation of your bleeder screws? Post a pic if possible.

Bleeders on Top. I've actually done that very thing before on a chevy axle swap

 

[JeepGuy]

Update: First off, All front end nuts and bolts will be tightened down prior to road testing this system. Most thing related to suspension and steering at still loose so don't freak out

New Center line arrived and went in without issue. I actually like the routing of the home made brake lines a bit better as they stay closer and a little tighter to the bump stop mounts. Thinking less things to snag on a bush or branch somewhere and if that is a problem, these were about as easy as can be to bend by hand. The kit I bought came with a total of 25ft so I have plenty left to change things if needed.

Next up was the Vacuum lines. Replaced the older PCV valve and old hose. That hose was rock hard and just asking to create a vacuum leak, but I kept it just in case this newer version causes issues with heater hose routing and valve.

Next up I pulled the MC off the booster again and checked the depth of the plunger. The Plunger from the MC is extended (threaded out) almost to the end of adjustment as it came from the supplier. I guess in a pinch, I could thread that all the way in, use the insert that came with the MC and potentially get a bit more adjustability out of the system. I'm just not sure the plunger that came with the system would adjust far enough back, and if I fully install the MC adapter, I have no idea how I'd get it out from the MC if it didn't allow enough space to mount the MC. Unfortunately I cannot find the paperwork that came with this MC, and I recall reading something in there about use of the adapter.

 

[JeepGuy]

So after install and doing a reverse bleed twice on all wheels, there were no bubbles coming from the MC and the fluid was visibly rising filling up the MC from the bleed. Had to empty (not completely) both wells at least once during the bleed, so I know there is plenty of fluid flowing from each end of the line.

Did multiple brake compressions with the engine off, and under power. No leaks visible yesterday or after sitting all night.

Onto adjusting everything which is where I'm assuming my pedal height, and travel come in to play.

The Booster came with the firewall-side knuckle extended pretty far back on the thread. The pin is just sitting in there with the cotter pin removed at the moment. I'm wondering if I need to adjust that knuckle closer to the booster, away from the firewall, which would rotate the assembly and pull the brake pedal rod out from the firewall. I'm not sure how far I could do this without having a pedal sticking way up in the cab, but I'm assuming there is adjustment (or should be) on the rod that actually attaches to the pedal.

At this point, there is still a ton of travel on the pedal, but it does stop the Bronco from moving under it's own power at idle. It has not been out of the driveway yet.

All that brings up another question. As it is now, the rear well of the MC is feeding the front brakes. While doing the bleeding and testing, I've noticed a significant amount of fluid movement to the front well of the MC, to the point where it will create a fountain if you press the pedal too hard. This occurs with engine off or on. Same thing was noticed during the reverse bleed. I had to depress the bleeder pretty slow to keep the fluid from shooting out the top of the front well (rear brakes). That never really occurred with the rear well of the MC that is feeding the front brakes. Also, I did not see any movement in the front brake calipers during the bleeding process (actually brake depression). Everything is new and still pretty tight, so I didn't expect to see massive movement but did expect to see something going on. Again, the brakes are stopping the Bronco at idle, but I haven't really tested to see if the front brakes are actually squeezing. I have gone over the install instructions and haven't found anything out of order. Could the lack of movement be due to everything being new, or is there something else potentially going on?

Should I pull the calipers of the brakes and check them under pressure to see if they are squeezing?

Is it possible the front well of this particular MC should be feeding the front brakes?

The pin on the front of the metering valve at the front of the proportioning valve does push out, but not enough for me to grab ahold of it and keep it extended. So as I'm bleeding this I guess there is a possibility that the front brakes are still not bled completely.

I know it's a vacuum system and the pedal will feel different than a non-vacuum assist, but it still seems like there is too much pedal movement before the brakes work.

 

[4xfun]

Do not pull the pads and press the brakes. The caliper pistons will extend too far and you may damage them.

I have seen several threads about a proportioning valve, a bleed tool for the pin, and issues with bleeding. Someone will point you to old thread. WH tech can also advise you on how theirs work and if you need to reset pin. The pin tool is less than $10, but I thought the pin was threaded in to hold the pin in place, rather than helping to pull the pin out.

I would make sure the proportioning valve pin is correctly reset before test driving or even checking your front brakes. Some of the issues that you were having with leaks may have caused the shuttle to move and shut off one side of the system. The valve is designed to make sure that one side of the system (front or rear) works if there is a failure in the other side.

Cracking the bleed screws with someone pushing on the pedal will tell you if you are getting any pressure on the front discs. You will see fluid come out and the pedal will drop. That only tells you if you are getting fluid. Jacking up the front end and trying to turn the tire with someone pushing on the brakes will tell you if the calipers are squeezing. I don't know of a way to test the proportioning valve other than to start driving is slowly and try to stop. Keep repeating the start/stop process until you can tell what the brakes are doing. If the front's are not working, the back will lock up before the front end dips. I am not sure what happens if the proportioning valve pin is not in the correct location or working correctly.

I would be a little concerned about the fluid movement in the bowl. It sounds like fluid is getting past the piston seals and pushing up into the master cylinder, but I don't think I have ever looked in mine when someone was pushing the brakes. If it is an issue, this should also be causing poor performance on that side of the system. It should also be causing a sinking pedal. Since you got it from WH, call on of their techs and ask if that is normal.

Good luck

 

[DirtDonk]

I admit that I don’t understand the full dynamics of what’s going on with the piston movement in a master cylinder, but fluid spurting up into one or both reservoirs is very common.
Probably completely normal in fact.
Sometimes it’s barely a dimple, sometimes it’s a full on squirt that’ll exit the master cylinder and get on your paint if you’re not careful! Sometimes there’s nothing, and sometimes it’s something in the middle of all those extremes.

What I don’t know, is whether a big squirt or a small ripple in the fluid indicates anything good or bad in the system.
Maybe someone else can enlighten us, in glorious gory detail, on the subject.

 

[4xfun]

Check out this article. It discusses some similar issues.

Disc Brake Help

OK guy's I installed a chevy disc brake kit from one of the vendors. Now for some reason the brakes are dragging excessively. Looks like the disc brakes are not retracting slightly after I let off the brakes. Anyone got any idea how to trouble shoot and fix this. For what it's worth the...

classicbroncos.com

I did some quick googling, and it looks like it is not uncommon to see some fluid movement. It is related to compensating ports in the MC. The ports let fluid move up into the MC chambers as it expands. The problem is that I did not find anything that quantified when it was an issue. If the brakes have good pressure under a stop condition that started off slow and then you pressed hard real quick, that should tell you if the MC piston is leaking. If the piston is leaking, it is not apply full force to the brake system.

 

[73azbronco]

any fitting, lube, tight lose tight lose tight to torque, my technique to prevent leaks.