How do you test Power Brake Booster

[barnett468 418]

On 9/4/2017 at 9:48 AM, prayers1 said:

Is there a specific test for the booster?

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

if this was with the engine off your booster is likely not leaking but you can also test it with a vacuum gauge . this should be done with the pedal up and then partially depressed.

my friend had mustang steve ship him a booster and 70 prop valve and both leaked. i am not impressed with mustang steve parts at all.

post your build specs and cam specs

are your brakes stock?

does your light in the instrument cluster work properly?

 

[1969_Mach1 333]

On ‎09‎/‎04‎/‎2017 at 8:54 AM, 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?

 

 

Let us know if you get any vacuum readings at idle in gear and/or under normal driving conditions.  If it drops to 9" or so in gear at idle your power brakes will not work very well.  I had one car a long time ago that only made only 9" of vacuum at idle in gear because of the long duration and large valve overlap camshaft.   When coming to a stop from speeds of 35 mph or more I would get one and rarely two brake applications with power assist.  After that it felt worse than manual brakes.  Valve overlap is needed but has a large influence on idle quality and engine vacuum.

Yes, the engine vacuum will drop under load.  I was curious what it is under normal cruise speeds, in town at 30 mph or so, and stopped with it in gear at idle.

barnett468, he posted a few cam specs at 0.050 tappet lift in his initial post.  No advertised specs which also influence idle quality and idle vacuum.  I might be wrong, but what I understand is it's a custom grind hyd. roller from Comp Cams.  Maybe you can offer some ignition timing suggestions that might increase the engine vacuum a little as well. 

[barnett468 418]

12" at idle is way too low for power brakes so you must have a huge cam.

[prayers1 153]

Cam is a special order CompCam, by Brent Lykins of B2motorsports. He specializes in Clevelands and speced the cam w/ pwr brakes in mind.

[prayers1 153]

Quote

Heres the Cam Card

 

[1969_Mach1 333]

I am most certainly not a camshaft expert.  That is a fairly large cam.  But you have a 408 stroker motor and I don't know what's best for those.  It is more cam  than I would run on a car that I want to have good street manners.  But that's just my personal taste as I am getting older.  What RPM range was this motor being built for?

Just a couple of guesses, with the early exhaust valve opening I'd think the exhaust is loud on that car?  And, it must have a rough idle with 75 deg and 13 deg valve overlap at 0.006" and 0.050" tappet lift respectively?

It's still a tough call, either there isn't enough vacuum at all to get any power assist or the booster is bad so you have absolutely no power assist.  Replacing the booster is easier to try.  Will Mustang Steve repair or replace the booster under warranty?  If so, I'd first try that.  At some point you will need a known good booster.  If a known good booster doesn't give you some or any assist, then you know there is simply not enough vacuum.

[prayers1 153]

That you 1969_Mach1, I appreciate all of your help!! You obviously have more Cam knowledge than me.

Yes, loud car with Flowmaster 40's, 5500-6000 rpm range, The motor is by far the best I ever had. Lots of power and quick to rev.

The idle is very rough, even in warm weather at first cold start up,  it takes a long time to get it to idle w/o feathering the pedal.

I would need to lift the left side of the motor to replace the MC & Booster, lots of work.

Mustang Steve no longer personally sells parts, a guy who worked for him took over and I had to get 3 different MC's before they sent the right one and it was their last. I was thinking the last ones are always some sort of blem, return or the black sheep of the bunch.

Who knows if the MC & Booster are well built.

Barnett said (this in response to me pulling the vac line off the check valve w/ the engine off and heard the escape of air): if this was with the engine off your booster is likely not leaking but you can also test it with a vacuum gauge . this should be done with the pedal up and then partially depressed.

How to do this test?? Tie in a vac line w/ gauge between the check valve? What am I looking for??

I really want to thoroughly test the booster before taking the motor apart. What do you suggest?

I rebuilt the port/dist valve could there be a hidden problem with that???

Appreciate any suggestions!

 

[1969_Mach1 333]

Other than the brake pedal method others have suggested, I don't know any other way to test the booster.  I think you can have a brake booster not work and still not leak vacuum.  Maybe barnett468 knows of other methods to test a brake booster?

Can't you simply remove the valve cover on the drivers side to get enough room to remove the master cyl. and brake booster?  I don't have a Cleveland, but on my car with a 351W and still the original booster, the master cyl. can be removed separately from the booster.  Then the booster can be removed by itself through the opening between the inner fender and the shock tower brace. I have to remove the hood hinge spring to get a little extra room, but that's simple to do. 

[prayers1 153]

I have taller than most VC's and I cannot get the rear bottom bolt out. When I pull the bolt up it hits the booster.

If I have too, I will cut the bolt rather than loosening all of the exhaust, motor etc, etc, etc....

[barnett468 418]

i can guarantee you that even if your booster is bad which i doubt, you will still not have good brakes at low rpm. if you want good brakes in stop and go traffic you will need a different cam or at least a vacuum pump and a reserve vacuum can.

you can test it with a vacuum pump.

[prayers1 153]

I already installed a reserve vacuum can

[1969_Mach1 333]

Remember though, a larger volume of vacuum at 12" will not improve anything.

[prayers1 153]

I don't understand. Isnt that what the Reserve Canister is for?

[1969_Mach1 333]

I understand the purpose of a vacuum canister, but I don't know that they can help much if the motor doesn't create a high enough vacuum signal.  It takes both a high vacuum signal and some volume for the brake booster to operate well.  I've only known one other person in a similar situation to try a vacuum canister.  There was very little improvement and they ended up installing an electric vacuum pump.

Drive the car with a vacuum gauge connected so you can read it while driving.  If you get high vacuum readings 15"-16" or more, like when coasting, you should have some power assist at that time.  If not, the booster is not working.  But, like barnett468 mentioned, even with a working brake booster, it will not work very well at low speeds with that cam.

[prayers1 153]

Ok I understand, Next time I take the car out I will that test. I wasn't sure what to watch for, now I know. THANKS!

[barnett468 418]

11 hours ago, prayers1 said:

I already installed a reserve vacuum can

they don't do a lot, and in your case i'm guessing you need a pump. the reserve can will work a little better with a pump.

[prayers1 153]

From what I'm gathering here, no matter what I do with the present system there will be no improvement.

If I was to revamp this system then what should I use with the existing front 70 disc/drum & Port/Dist valve set up.

 

[Grabber70Mach 107]

Maybe a  Hydroboost setup?

[barnett468 418]

11 hours ago, prayers1 said:

From what I'm gathering here, no matter what I do with the present system there will be no improvement.

If I was to revamp this system then what should I use with the existing front 70 disc/drum & Port/Dist valve set up.

 

ok let me clear this up. if you have stock brakes and 12 inches of vacuum at idle because of a huge cam, your brakes will totally suck in stop and go traffic or if you pump them to stop.

[prayers1 153]

First off, When I go for  a test ride to test my vacuum, should I tee the gauge between the manifold vacuum and booster OR do you want me to ONLY test manifold vacuum???

In my case, I have very little real estate in the engine compartment , in fact I had to install the reserve canister up in the wheel well.

Knowinging this, what would be the best to use an electric pump or Hydro Boost?

I have very little knowledge of each, so if someone can basically explain that would help all who read this thread.

THANKS!

 

 

[det0326 179]

Doesn't the Hydro Boost use pressure from the power steering pump, if so you need to check out the effect it may have on the integral steering box, I believe you said you had because from what I understand these aftermarket steering  systems require more from the pump already.. I am in the same place you are with mine and knowing what I know now I wish I had just used manual pedal and M/C I believe I would be a world ahead and better brakes to.  

 

I would put the gauge between the booster and manifold to see what the vacuum is reading when the brakes are in use too.

 

[1969_Mach1 333]

For your situation of trying to keep the engine compartment clean for local car shows, I wouldn't use a hydro boost system.  We use to own a 1996 Mustang GT and it used a hydro boost power brake system and it worked just fine.  But they take up more space and there are several additional hydraulic hoses that are tied into the power steering pump.  Ours had 4 hydraulic hoses going to the hydro boost unit.  Also, if you are still using a stock Ford power steering pump, I don't think its sufficient for both power steering and hydro boost.

If, during your test drives with a vacuum gauge attached, you determine the vacuum booster is absolutely not working, since it's an original Bendix booster I would have it rebuilt.  Then, if there still isn't enough power assist for your preference and you don't want to do a cam swap, look into installing an electric vacuum pump somewhere, maybe in the trunk, in conjunction with the vacuum canister you already installed.  I've heard they can be noisy, so do some research and don't get the least expensive you can find. 

[prayers1 153]

det0326_ I already had the manual brake set up  using the Maverick MC and a separate rear port valve. Using the same 70 disc/drum I have the manual stopped the car but with great effort.

I think the way to go is with a electric vac set up but they are pricey.

[ray1970 88]

Same but different.

 

[ray1970 88]

What you want is this one......