How do you test Power Brake Booster

[prayers1 153]

 

Before I blame the Cam I want to make sure the Booster isn't defective.  With the engine running, I do not get the feel of a power brake pedal. I know if there is not enough Vacuum you would have pedal fade when pressing down on it long enough. The pedal right from the start feels like a manual pedal which I had before. I was concerned this might happen, but the guy who designed my cam said it would work with Pwr Brakes, I upgraded to stock 1970 Pwr Brake Booster and Master Cylinder.

The cam is 602/574-235/241- IC 112, with 12" of vac.

I thought to put a Vacuum booster canister in, but I believe that would work if I ONLY had a slight feel of a Pwr pedal from the start.

I have vacuum direct from the Manifold and PCV is connected to the back of the carb.

Thanks in advance!

[rwcstang 201]

2 hours ago, prayers1 said:

 

Before I blame the Cam I want to make sure the Booster isn't defective.  With the engine running, I do not get the feel of a power brake pedal. I know if there is not enough Vacuum you would have pedal fade when pressing down on it long enough. The pedal right from the start feels like a manual pedal which I had before. I was concerned this might happen, but the guy who designed my cam said it would work with Pwr Brakes, I upgraded to stock 1970 Pwr Brake Booster and Master Cylinder.

The cam is 602/574-235/241- IC 112, with 12" of vac.

I thought to put a Vacuum booster canister in, but I believe that would work if I ONLY had a slight feel of a Pwr pedal from the start.

I have vacuum direct from the Manifold and PCV is connected to the back of the carb.

Thanks in advance!

you know, Im curious aswell, I've looked at youtube for similar tests but the issue I get is sometimes a hard pedal and I hear a hiss when I apply & hold the brakes. so I think I may have a bad booster or vacuum leak somewhere. 

[1969_Mach1 333]

prayers1:  If you truly have 12" of vacuum at idle, you should have some power assist.  My 351W makes 14" of vacuum and the power brakes work great.  Many years ago an older mechanic told me if you lightly press down on the brake pedal, maybe an inch or so, then start the engine, a properly operating vacuum brake booster will try to pull the pedal down slightly under your foot.  I.E. you will feel the pedal pressure against your foot decrease.  I've tried that simple test on several cars with good operating vacuum power assist brakes and it works.

Do you ever have any power assist?  Like on the first brake application after letting off the gas pedal?  When I was younger I had a Dodge Challenger that made only 9" of vacuum at idle.  I would still get good power assist after letting off the throttle.  And then usually 3 more good power assist brake applications with the car idling like at a stop light. 

rwcstang:  If you hear a hiss while holding the brake pedal down, your power brake booster is leaking.  It's best to have it rebuilt instead of buying an aftermarket replacement or rebuilt booster.

[rwcstang 201]

33 minutes ago, 1969_Mach1 said:

prayers1:  If you truly have 12" of vacuum at idle, you should have some power assist.  My 351W makes 14" of vacuum and the power brakes work great.  Many years ago an older mechanic told me if you lightly press down on the brake pedal, maybe an inch or so, then start the engine, a properly operating vacuum brake booster will try to pull the pedal down slightly under your foot.  I.E. you will feel the pedal pressure against your foot decrease.  I've tried that simple test on several cars with good operating vacuum power assist brakes and it works.

Do you ever have any power assist?  Like on the first brake application after letting off the gas pedal?  When I was younger I had a Dodge Challenger that made only 9" of vacuum at idle.  I would still get good power assist after letting off the throttle.  And then usually 3 more good power assist brake applications with the car idling like at a stop light. 

rwcstang:  If you hear a hiss while holding the brake pedal down, your power brake booster is leaking.  It's best to have it rebuilt instead of buying an aftermarket replacement or rebuilt booster.

@1969 Mach1 thanks for the tip, I figured a rebuild is in order and luckily there is a place 15 miles away from me that rebuilds them. 

[MAC390 327]

Sounds like the booster is leaking.Rebuild time.

[LoneWolf2U 136]

Simple test for booster operation.

With engine off, depress brake petal a few times till all assist is gone.

With foot on brake petal pressing downward, Start engine. If the booster is working your foot will drop slightly as power assist is returned to booster.

[Ridge Runner 1,112]

Start the motor and let it run for a minute ,shut the motor off ,pull the valve out of the booster ,if it hisses the booster is good ...unless the valve is bad 

[prayers1 153]

I will have to try the testing tomorrow. But wanted to throw out there that I have NO assist. It just feels like manual brakes.

The Booster and Master are from Mustang Steves, I believe the booster is rebuilt.

[Ridge Runner 1,112]

Check the valve ,remove it from the booster and hose ,if you do not have a vacuum tester suck on the hose side and it should have very little resistance ,you should not be able to blow through it ,it is a one way valve . If you can blow through it the valve is bad . If you do have a tester test it in the booster to see if it holds vacuum if you cant blow through it .if the valve is good and it still does not hold vacuum the booster diaphram is probably bad

[Mach1 Driver 560]

Hey Prayers, just some booster info I've learned, but don't know if this will necessarily help. Some time ago my booster started mooing like a cow when I first applied the brakes- and I couldn't figure out what was causing it. LOL, it gives one long moo and then it goes away and it always operates normally. I've suspected that it needed a rebuild- it's original, but it keeps on mooing along. In a video by WCCC, the owner Don states that they need a rebuild every 10-15 years, guess mine is past its expiration date at 48. They have a guy that will rebuild your original, otherwise getting the correct one is problematic according to Don as there is lots of inaccurate information out there. Its video #7 and may give you some helpful information.

[1969_Mach1 333]

23 hours ago, prayers1 said:

 

Before I blame the Cam I want to make sure the Booster isn't defective.  With the engine running, I do not get the feel of a power brake pedal. I know if there is not enough Vacuum you would have pedal fade when pressing down on it long enough. The pedal right from the start feels like a manual pedal which I had before. I was concerned this might happen, but the guy who designed my cam said it would work with Pwr Brakes, I upgraded to stock 1970 Pwr Brake Booster and Master Cylinder.

The cam is 602/574-235/241- IC 112, with 12" of vac.

I thought to put a Vacuum booster canister in, but I believe that would work if I ONLY had a slight feel of a Pwr pedal from the start.

I have vacuum direct from the Manifold and PCV is connected to the back of the carb.

Thanks in advance!

First, check the engine vacuum at idle to the brake booster like others have mentioned.

Second, if vacuum is low, your cam already had 14 degrees overlap at 0.050" tappet lift.  If your motor is still 351 cubic inches, that is a lot for street driving and power brake operation.  What is the advertised duration, and is it at 0.004" or 0.006" tappet lift?  Just my opinion, I used to think custom grind cams were better than off the shelf stuff.  And they often are for a race application.  But for a street driving car, the off the shelf stuff from companies like Comp, Crane, Isky, and Lunati have been through R and D, and tested on motors in addition to computer designing.  So you have a better idea of what you are getting. 

Third, not affecting the power assist, but do you have a 1970 brake pedal to go with the 1970 vacuum booster?

[RPM 1,190]

Not knowing the history of your car I'll ask, do you have the proper pedals and pushrod for your application?

[prayers1 153]

I got the pedal, booster and master cylinder from Mustang Steve. He sells a kit on his website.

Mach1 Driver, I remember the Booster would mooo with every push of the pedal when I did the first bleeding of the brakes, it had no vacuum hooked up.

Its a 351C stroked to a 408 the IC is 106, roller cam from Comp Cams

I have a 1969 Mustang and used the rod that drops down on the brake pedal. I believe the 1970 uses a straight rod.

I'm using a 1970 Master cyl, Dist block and 1970 front disk calibers.

[1969_Mach1 333]

Well at this point I would say if you have 12" or more of vacuum to the booster at idle, the booster is probably bad.  Double check the check valve at the booster.

How did you remove and swap the push rod's from the back of the boosters?  As far as I know, they are not removable from the OEM boosters.  Mine cannot be removed.

[Max Power 74]

On 7/22/2017 at 11:09 AM, Mach1 Driver said:

Hey Prayers, just some booster info I've learned, but don't know if this will necessarily help. Some time ago my booster started mooing like a cow when I first applied the brakes- and I couldn't figure out what was causing it. LOL, it gives one long moo and then it goes away and it always operates normally. I've suspected that it needed a rebuild- it's original, but it keeps on mooing along. In a video by WCCC, the owner Don states that they need a rebuild every 10-15 years, guess mine is past its expiration date at 48. They have a guy that will rebuild your original, otherwise getting the correct one is problematic according to Don as there is lots of inaccurate information out there. Its video #7 and may give you some helpful information.

Interesting. In all the years I have been playing with these cars, rebuilding the booster every decade or so has never been an issue. I think that is a pretty aggressive recommendation. I would hazard to guess that most unmolested cars here are running their original boosters with no issues.

[1969_Mach1 333]

I thought in the WCCC video he was referring to the early 1969 and older Midland brake boosters needing a rebuild about every 10 years.  According to WCCC the Midland boosters provided more assist but were not as reliable as the late 1969 and newer Bendix boosters.

It might be prayers1 has a bad booster.  But at this point I am still not certain if prayers1 has enough vacuum to the booster or has the correct combination of parts.  Maybe I missed something, but I don't think those questions have been cleared up.  According to WCCC if a 1969 pedal is installed with a 1970 booster or a 1970 pedal is installed with a 1969 booster, the boosters rear seal will be ruined with just a few ( I think he said about 5) brake applications because the rod from the pedal to the booster will be pushing at an angle.

[Mach1 Driver 560]

2 hours ago, Max Power said:

I would hazard to guess that most unmolested cars here are running their original boosters with no issues.

Well, if you don't mind the moo!

34 minutes ago, 1969_Mach1 said:

I thought in the WCCC video he was referring to the early 1969 and older Midland brake boosters needing a rebuild about every 10 years.  According to WCCC the Midland boosters provided more assist but were not as reliable as the late 1969 and newer Bendix boosters.

It might be prayers1 has a bad booster.  But at this point I am still not certain if prayers1 has enough vacuum to the booster or has the correct combination of parts.  Maybe I missed something, but I don't think those questions have been cleared up.  According to WCCC if a 1969 pedal is installed with a 1970 booster or a 1970 pedal is installed with a 1969 booster, the boosters rear seal will be ruined with just a few ( I think he said about 5) brake applications because the rod from the pedal to the booster will be pushing at an angle.

yep yep all good points. Food for thought Prayers.

[skidmarky 50]

If the diaphragm is shot in the booster it will cause a vacuum leak and make your engine run like poo. Simple test, unplug the vacuum line to the booster, start the car and plug it with your thumb, engine run better?

[prayers1 153]

I ordered a black plain vacuum canister from Summit. Who would of thought that when I received it, it had JEGS Stamped in the metal on top of the tank.

I installed it in the upper rear section of the left front wheel well, drilled 2 holes to run 3/8ths Fuel line and rubber grommets.

FYI I have 12" of vacuum.

Took the car for a spin and I did feel use use of power brakes but was very disappointed. Not mush of an improvement over Manual. Maybe I so use to modern pwr Brakes that I expected to feel the same.

I rebuilt the Port valve, installed new Auto/pwr brake pedal, rebuilt Booster and MC. I have all new SS lines with 1970 Front disc setup.

I assume all is working as should based on the performance of a 1969 Car.

Thanks all for your feedback and help!

[1969_Mach1 333]

I think there is still something not quite right.  My 1969 Mach 1 with factory power front disk brakes has a tremendous amount of assist.  Motor makes 14" of vacuum at idle.  The brake booster is the original Bendix booster that I had rebuilt.  I think you either have a bad brake booster or not a high enough vacuum signal to it.  Is your 12" of vacuum at idle in gear?  If that is in neutral, what is it in gear?  It will be less in gear.  Have you driven the car with a vacuum gauge connected using a long hose?  Rig it so the windshield wiper holds the vacuum gauge against the windshield and you can see it while driving.  You will get an ideal of the vacuum your motor creates under different driving conditions.

I've only known one person to try a vacuum canister when their motor didn't make enough vacuum and their result was like yours.  The canister did not help much.

[prayers1 153]

Well I don't know what to say. I ordered the Booster, MC and brake pedal from Mustang Steve who has been selling this combo for years. Both booster and MC are rebuilt.

I know I have the correct booster & rod and the correct brake pedal.

I tested the  check valve At the booster and it works fine.

Yes, 12" of vac is in PARK. I can rig a vacuum line w/ a gauge to see how it responses when driving. But shouldn't the vacuum drop anyway under power?

 

 

[det0326 179]

Hi John

Not sure what the Mustang Steve power booster looks like. is it the pancake style or more like an original?  I used the pancake style on mine and I am making about the same vacuum you are (12-13) and mine has very little assist. I think it is a 9" dia. It gave me a lot of room between the M/C and shock tower but after installing it I have heard they don't work as well as the original.  

[Bob & Sue 110]

52 minutes ago, prayers1 said:

Well I don't know what to say. I ordered the Booster, MC and brake pedal from Mustang Steve who has been selling this combo for years. Both booster and MC are rebuilt.

I know I have the correct booster & rod and the correct brake pedal.

I tested the  check valve At the booster and it works fine.

Yes, 12" of vac is in PARK. I can rig a vacuum line w/ a gauge to see how it responses when driving. But shouldn't the vacuum drop anyway under power?

I'm sure you've seen this video goto the bottom of the page.

I have the Bendix on mine with 14 vacuum at idle, it will stop ya almost as well as new car brakes, something is amiss with you system I'd be leaning towards your booster. Even new or rebuilt boosters can be bad out of the box I've had it happen took a couple weeks to figure it out.

 

http://www2.cougarpartscatalog.com/store/p/16072-Brake-Booster-Midland-Power-Brake-Rebuilt-1967-1969-Mercury-Cougar-/-1967-1969-Ford-Mustang-clone.html?attribs=77

[prayers1 153]

It's the original smaller Bendix booster. I have a feeling that its suppose to feel like this. I believe we are spoiled with the ones we have in our modern cars.

I would like to get more feedback by others w/ Pwr Brakes and see what the say about the assist.

Replacing either the MC or Booster is a big project in my car. The valve cover almost hits the booster and the bottom rear Valve Cover bolt will not come out unless I shift the motor to the right, Very tight clearance.

Is there a specific test for the booster?

I did pull the valve off the booster and heard a loos of air.

[Bob & Sue 110]

Watch that video in my previous post.

Pump the brake pedal 5-6 times engine off keep foot on pedal start car pedal should move slightly with vacuum boost assist.