Brake Booster Losing Pressure with Engine Running

[ntsqd]

Some points that may or may not still apply.

Banjo bolt sealing washers; you can re-use old ones if they're not too grooved or damaged by heating them with a propane torch until they glow just a little. I hang them on a piece of wire and once they're almost glowing drop them into a Red* Solo Cup that is ~1/2 full of water. Unlike if you did this to steel it makes either aluminum or copper washers dead soft and they will seal properly.
*Cup color is crucially important to Country fans, not so much to others.

If you're questioning the pressure at the calipers then buy or build something like this: https://www.summitracing.com/parts/wil-260-0966 to get a pressure reading at the bleed nipple.

The day that I started using a hydraulic flaring tool (MasterCool brand in my case) was the day that my random leaking inverted flares stopped occurring. I have yet to have it make an off-center flare. Not cheap, but worth it if you periodically are going to be doing this sort of work.

Annealing of the SS flares might have got them to seal, but since the easy availability of the Cupro-Nickel tubing I don't bother with SS tube for brakes.

 

[JeepGuy]

Update:

Well, it's not perfect but the brakes definitely work.

I went back through and double checked all the joints. No leaks.

Jacked up the front and spun the tires, press the brakes, they stop.

Double checked the gap on the calipers after the install... Looks correct as there is probably 3/16" to 1/4" clearance, hard to tell from pictures.

Went on the Jungle website and ordered up a Vacuum Tester. Advertised to work on Engine vac as well as fuel pressure... Either way, I definitely have vacuum pressure at the booster. Only measured it at idle.

Road tested the Bronco and it does stop. I think I'm to the point of tuning in the pedal height. Still haven't really jammed on them as this was the first road test for the Bronco in a very long time and I'm checking for all kinds of things, not just brakes.

Thank you to all of the input in here.

 

[ksagis]

I get my conical crush washers from Crown Performance in Vista, CA, and keep some on hand for emergencies.

Looked them up today and realized they are close to my dads house in Escondido. May swing their shop the next time visiting him.

This is the website, correct? Unless I am blind, not seeing them on the website. Thanks again for the tip on the vendor

https://www.crownperformance.com/

 

[nutter3]

20 years ago, I had the same issues with stainless lines leaking on my 73 bronco. They all rounded off the tube nut long before they sealed. I think I ended up just using vice grips to get them tight enough to not leak. I was not impressed. Everything I do now with brakes, I use Ni-Cu brake line.

 

[Apogee]

Looked them up today and realized they are close to my dads house in Escondido. May swing their shop the next time visiting him.

This is the website, correct? Unless I am blind, not seeing them on the website. Thanks again for the tip on the vendor

https://www.crownperformance.com/

That's the place. I get all of my brake hoses from them for my business, and I'm pretty sure those crush washers are kind of a specialty bulk item. I bought a few hundred a few years ago, so I don't know if it's still a current stock item or not.

FWIW, 13+ inHG of vacuum is not awesome for brake assist boosters. In general, 18+ inHg would be ideal, 15+ inHg is typically pretty good and 12-15 inHg can be serviceable, however may require additional measures such as vacuum canisters/accumulators, auxiliary vacuum pumps, etc.

 

[JeepGuy]

That's the place. I get all of my brake hoses from them for my business, and I'm pretty sure those crush washers are kind of a specialty bulk item. I bought a few hundred a few years ago, so I don't know if it's still a current stock item or not.

FWIW, 13+ inHG of vacuum is not awesome for brake assist boosters. In general, 18+ inHg would be ideal, 15+ inHg is typically pretty good and 12-15 inHg can be serviceable, however may require additional measures such as vacuum canisters/accumulators, auxiliary vacuum pumps, etc.

Yeah, that is at idle. I'm going to mess around with the timing a bit today if I can get around to it. I didn't replace the points or adjust the timing it had in it from when I bought it a couple decades ago... so I'm guessing a bit of tune up is needed. After a bit of reading I'm thinking of just going out, hooking the vacuum guage back up, and setting time based on that and seeing what that does. This is far from a daily driver at the moment, but I'd like it to be in the near future. I have no idea what cam is in this, but It starts and idles very smooth at the moment. Hopefully I don't screw that up...

Road testing reveals weak brakes, but it they are functioning... So progress continues.

 

[JeepGuy]

Update on this. Got around to putting a timing light on the Bronco. I have not done anything to the ignition system since I bought it, but everything regarding the distributor cap, points, condenser, and coil all seem to be functioning properly. Luckily this Bronco has lived the majority of it's life that I've owned it inside the garage out of the elements which I think has helped keep things in order.

I disconnected the vacuum advance from the carb to distributer and my timing originally was set right at "0." I adjust idle to about 13-15 degrees BTDC and ran it up to about 3200 -3500 rpm. Ignition moved up to between 30-35 advance.

I do not have a tach installed so I'm getting these rpm numbers from the timing light.

After setting the timing I rechecked the vacuum at the booster and at idle it is almost 17-18. Add some throttle and it climbs. On the gauge this puts it in the normal vacuum operating range. There was a noticeable difference in the brake pedal after everything was set, but still does not seem to have a real hard bite. And on a positive here, no visible leaks anywhere in the system after another 5 or so miles of road testing.

I'm considering ordering up an adjustable brake pedal rod and trying to dial in the optimal pedal stroke with that.

The saga continues...

 

[ntsqd]

Maybe I've missed or have forgotten it, but you have confirmed the booster to m/c piston relationship?

Remind me again, which front calipers and what bore m/c?

Every engine is a little different, but all of my SBF's seemed to run the best at 12° BTDC. 2° too little timing can't hurt you, but 2° too much timing sure can.

 

[Brush Hog]

You might not be used to the feel of power disc brakes in your bronco if you converted from manual or manual drum brakes. Took me a couple drives to get used to front power discs after converting from power drum. As long as they stop you I’d say drive it and see if maybe you get used to them.

 

[JeepGuy]

Maybe I've missed or have forgotten it, but you have confirmed the booster to m/c piston relationship?

Remind me again, which front calipers and what bore m/c?

Every engine is a little different, but all of my SBF's seemed to run the best at 12° BTDC. 2° too little timing can't hurt you, but 2° too much timing sure can.

Yes. The combo (booster and MC) I bought was the standard combo from WH. The front calipers are based off of a 76 Chevy I believe. It was also part of their front-end brake kit for a dana 30 or 44. The master cylinder is the HD aluminum one from WH with a 1 1/8" bore.

I'll go back out and see if I can get a better read on the timing. I really don't think blowing up the motor would be a good thing

 

[ntsqd]

SBC's do tend to want a little more initial than SBF's, although both like to have about the same total.

If they're the Chevy calipers then they're a 2-15/16" OD piston. Out of curiosity, have you tried pulling the booster check valve out of the booster and then trying the pedal that way? That would yield about an 82:1 total (hyd + pedal) leverage ratio, which is pretty stiff. For pure manual brakes you'd want it closer to 95:1. For vacuum boosted brakes operating correctly that's probably about the right ratio.

 

[DirtDonk]

Update on this. Got around to putting a timing light on the Bronco. I have not done anything to the ignition system since I bought it, but everything regarding the distributor cap, points, condenser, and coil all seem to be functioning properly.

In theory…

Luckily this Bronco has lived the majority of it's life that I've owned it inside the garage out of the elements which I think has helped keep things in order.

It definitely does. Other than the ethanol in the gasoline these days, which really messes with fuel pumps and carburetors.
And frankly, points and condensers don’t stay in tune forever, or even half of forever without constant tweaking and twiddling.

I disconnected the vacuum advance from the carb to distributer and my timing originally was set right at "0." I adjust idle to about 13-15 degrees BTDC and ran it up to about 3200 -3500 rpm. Ignition moved up to between 30-35 advance.

Seems about right.

I do not have a tach installed so I'm getting these rpm numbers from the timing light.

You can’t always guarantee those, but they should be pretty darn close most of the time. Heck, you can’t always guarantee a tachometer is accurate either.

After setting the timing I rechecked the vacuum at the booster and at idle it is almost 17-18.

That’s pretty decent, but it could be even better. Stock, it would’ve easily pulled 20 to 21.
I wonder if your timing marks are accurate? Have you posted up any pictures of that area of your engine yet? If not, can we see how the timing marks and pointer are oriented?

Add some throttle and it climbs. On the gauge this puts it in the normal vacuum operating range.

Is this back with the Advance connected, or still disconnected from vacuum?
Is the 17 or 18° below that normal line?

There was a noticeable difference in the brake pedal after everything was set, but still does not seem to have a real hard bite.

Kind of the same as my Chevy setup. What tire size are you running again?

And on a positive here, no visible leaks anywhere in the system after another 5 or so miles of road testing.

Small victories add up!

I'm considering ordering up an adjustable brake pedal rod and trying to dial in the optimal pedal stroke with that.

I don’t see how that can change the stroke. Only where the stroke starts. Where is the pedal right now, in relation to the floor?

 

[DirtDonk]

Yes. The combo (booster and MC) I bought was the standard combo from WH.

Were they already bolted together, or separate? If separate, I think the question asked was leading up to whether or not you’re at the proper gap set up between the rod and piston.

The front calipers are based off of a 76 Chevy I believe.

Yes. Ish…

I'll go back out and see if I can get a better read on the timing. I really don't think blowing up the motor would be a good thing

I don’t think blowing up the motor is in the cards. I run my Advance up to 21° one time just to see how it would run. Kind of pooped out early, but I didn’t blow anything up. And you won’t either, unless you drive it heavily while it’s pinging.
Listen to theforce Luke. Listen and feel how it’s running. Driving around the block isn’t gonna do damage unless you’re going animal on it.

 

[toddz69]

Looked them up today and realized they are close to my dads house in Escondido. May swing their shop the next time visiting him.

This is the website, correct? Unless I am blind, not seeing them on the website. Thanks again for the tip on the vendor

https://www.crownperformance.com/

I have some of Crown's hoses on my truck too. Great business!

Todd Z.

 

[JeepGuy]

In theory…

It definitely does. Other than the ethanol in the gasoline these days, which really messes with fuel pumps and carburetors.
And frankly, points and condensers don’t stay in tune forever, or even half of forever without constant tweaking and twiddling.

Seems about right.

You can’t always guarantee those, but they should be pretty darn close most of the time. Heck, you can’t always guarantee a tachometer is accurate either.

That’s pretty decent, but it could be even better. Stock, it would’ve easily pulled 20 to 21.
I wonder if your timing marks are accurate? Have you posted up any pictures of that area of your engine yet? If not, can we see how the timing marks and pointer are oriented?

Is this back with the Advance connected, or still disconnected from vacuum?
Is the 17 or 18° below that normal line?

Kind of the same as my Chevy setup. What tire size are you running again?

Small victories add up!

I don’t see how that can change the stroke. Only where the stroke starts. Where is the pedal right now, in relation to the floor?

Okay, first off how are you able to break up your quoted response line by line?

The timing marks are on the harmonic balancer and the degree indicator is just a little triangle mounted to the block. I think it's pretty standard. I took #1 spark plug out and confirmed visually (moving crank back and forth while looking into cylinder) and TDC seems very accurate on the timing marks. All I did was use a sharpie to "enhance" the marks so I could actually see them.

All of the timing I've done while moving the distributor has been done with the vacuum advance disconnected at the carb. All of the EGR stuff on this engine was deleted prior to me owning it, so my vacuum source for the distributor comes from directly under the front left corner (looking at it from the front of the Bronco) right below the fuel inlet. According to at least one of the various vacuum line routing diagrams, that is where it would have been pulled from anyways. I reset base to 12 degrees advance. First set the timing light to 12 then checked it against a solid "0" on the balancer, then set the timing light to zero and confirmed it then read "11-13" on the balancer. I can't really tell much of a difference in engine performance other than a slightly different smell from the exhaust. Kind of weird, but the further advanced exhaust smelled hotter (think hair dryer) versus just good ol un burnt gasoline .

I'm running 35" x 12.5" BFG's. 17" Indy wheels.

While driving around yesterday I could tell a huge difference with a little RMP added regarding my braking power. Sitting at stop lights the pedal would get pretty soft and at one very long one actually bottomed out. Bronco never lurched forward, but I believe my idle is a bit off. I probably need to adjust it a bit more so with the bronco in gear it's staying a little higher.

Brake pedal height isn't bad, I'm just not 100% sure I'm getting all that I can out of it. Which is why I'm considering the adjustable brake rod. I've pretty much maxed out the pedal height adjustment available on the booster side rod.

 

[JeepGuy]

Were they already bolted together, or separate? If separate, I think the question asked was leading up to whether or not you’re at the proper gap set up between the rod and piston.

Yes. Ish…

I don’t think blowing up the motor is in the cards. I run my Advance up to 21° one time just to see how it would run. Kind of pooped out early, but I didn’t blow anything up. And you won’t either, unless you drive it heavily while it’s pinging.
Listen to theforce Luke. Listen and feel how it’s running. Driving around the block isn’t gonna do damage unless you’re going animal on it.

Both bought from WH according to their sales records but not as a built kit. I don't remember the details of that purchase, but I think I bought them that way because I didn't need the whole preassembled set with the mounting bracket. Either way, it is a combo of MC and Booster commonly sold by them. Difference is they didn't set it up and bolt it together. I'm living on the edge over here.

 

[DirtDonk]

Okay, first off how are you able to break up your quoted response line by line?

Haha! Fortunately, Jon (admin) made it even easier than it was before, when he updated the software a couple of years ago.
All you need to do, after you hit the "reply" button to get the quotes, is put the cursor where you want to break a paragraph or subject, then when you hit ENTER (or RETURN in some cases?) it automatically separates the part you want to individually quote, from the rest.
So for this most recent reply, I put the cursor after the word "line?" in your question, then hit the enter button. Voila!

The timing marks are on the harmonic balancer and the degree indicator is just a little triangle mounted to the block. I think it's pretty standard. I took #1 spark plug out and confirmed visually (moving crank back and forth while looking into cylinder) and TDC seems very accurate on the timing marks. All I did was use a sharpie to "enhance" the marks so I could actually see them.

Yep, looks like pretty standard Bronco livery. Should be ok then, as long as the outer damper ring has not slipped.
But aside from slipping, it sounds like your visual test with the piston confirms that you're still there. Or at least close enough for now.

I can't really tell much of a difference in engine performance other than a slightly different smell from the exhaust. Kind of weird, but the further advanced exhaust smelled hotter (think hair dryer) versus just good ol un burnt gasoline .

That's a very interesting observation! Glad you pointed it out, but I can't tell you from my own experience whether it's a good thing, or a bad thing.
Maybe others will have some input on the subject.

I'm running 35" x 12.5" BFG's. 17" Indy wheels.

Did we already discuss whether or not you have verified your gear ratio? This could be very important to your performance concerns. Those 35's with any but the perfect gear ratios could be very sluggish in the acceleration department.
Especially if you still have 3.50's in the diff!

While driving around yesterday I could tell a huge difference with a little RMP added regarding my braking power. Sitting at stop lights the pedal would get pretty soft and at one very long one actually bottomed out. Bronco never lurched forward, but I believe my idle is a bit off. I probably need to adjust it a bit more so with the bronco in gear it's staying a little higher.

Need to verify two things.
Get your idle where it should be, but a little higher for good vaccum is not the end of the world.
But a slowly descending pedal usually means that there is a leak somewhere in the system. Usually in the master cylinder, but not exclusively to that. Or at least that's my take on it.

Brake pedal height isn't bad, I'm just not 100% sure I'm getting all that I can out of it. Which is why I'm considering the adjustable brake rod. I've pretty much maxed out the pedal height adjustment available on the booster side rod.

View attachment 941641

Got it. Thanks for the clear pic of the linkage.
Maybe someone with more power brake experience can lesson us on whether the geometry at the cantilever is compromised, or is just fine.

View attachment 941642 View attachment 941643

Pedal almost looks a little high to me. At least from here. But maybe that's due to no floor covering at all.
Not that it's a bad thing, but I would think you could get a lower pedal and get your linkage back down a bit, while still having enough pedal travel to work the brakes.
So here again, it comes back to the pedal traveling more than it should. Perhaps.
Here's where you get a measurement to the floor on yours, and some others with power brakes can measure theirs to see how they compare.
Didn't someone do that in this thread already? Or was that somewhere else I am remembering seeing it?

Paul

 

[DirtDonk]

Both bought from WH according to their sales records but not as a built kit. I don't remember the details of that purchase, but I think I bought them that way because I didn't need the whole preassembled set with the mounting bracket. Either way, it is a combo of MC and Booster commonly sold by them. Difference is they didn't set it up and bolt it together. I'm living on the edge over here.

Hah! Yep, exciting life you have, fiddling with Bronco brakes!
But, that's all the more reason to check, double-check, and even triple-check the distance from the booster rod to the back of the piston.
So, since my memory is bad at this kind of thing, refresh my memory on that subject. Did you check the distance? Was that you, or someone else here that recently bought one of the checking tools?
Either way, it's the tiniest of gaps that you want to have. Almost nothing, in the macro-world of truck brakes. You don't want them touching, but you don't want the rod to move far before it's pushing the piston.

Paul

 

[ntsqd]

I have recently suggested the purchase of the booster rod to m/c piston distance checking tool in a couple different threads. I've even more recently learned that those tools aren't always as simple to use as it would seem. Let's find out more about the situation before deep-diving into those nuances.

 

[DirtDonk]

Here is my simple, tool-less method of checking the gap.
Remove the two nuts holding the master cylinder to the booster.
Pull the master slightly away from the booster.
Adjust the rod out something minimal. Say one turn.
Gently push the master back in place and see if it bottoms out on the rod. If the rod touches down before the master cylinder is seated, turn the rod in half a turn and re-check.
If, after turning the rod out one turn, the master still does not touch down on the rod, repeat, and adjust out one more turn.
Repeat this until you actually can detect the master cylinder bottoming out on the rod, before it bottoms out on the mating surface of the booster.
When you get to this point, turn the rod back in half a turn, or until it no longer touches the piston first.

Someone here will probably remember, or you can look it up in the book, to see what the actual gap specification is supposed to be. It’s pretty minimal though, so keep that in mind.
When you’re satisfied that the booster rod is not touching the piston, but is just barely clear of it, lock things back down and take it for a test drive.

This has been pretty precise over the years for me. It is certainly not “by the book“ or kosher from a mechanic’s standpoint. But it has never let me down.