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Old 08-10-2011, 12:22 AM
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byersmtrco byersmtrco is offline
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Mmmm. I don't think it's a vacuum issue. Is the pedal hard?
If you give it both feet, will it lock up?

Are you running anything non-stock in the engine that might change (or decrease) the manifold vacuum?
What style booster are you running? It's not one of those under-dash things is it? Notice how Ford only used those for a couple years?
Hmmmmm !!!
John Byers
1960 Convertible (Orig owner)
Pic of car with my son Justin (15 Y/O 6'1")
Poss 3rd Gen T/B owner
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Old 08-10-2011, 10:38 AM
davidmij davidmij is offline
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The pedal is hard John, and if i stomp on the pedal with both feet it still won't lock up.
Even if the system was all drum, orignal without power brakes I should be able to lock them up.
Once again, here is the system I bought,

If I start the engine while holding the brake pedal I can feel when the booster kicks in and the pedal drops a little just like it should. Does anyone know if that is a true and complete test that the booster is working? Or could it still be bad even though the pedal acts correct?
The engine is stock, but it sat for 15 years so it runs rough. The vacuum messured good. I need to find out if there's a way to meassure the brake line pressure at the calipers - then I'll know if I'm getting the "power brake" that I'm supposed to. Does anyone know how to meassure that?
thx to all, Dave
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Old 08-10-2011, 10:09 PM
ncbird ncbird is offline
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Default trouble shooting

Go to the MBM brake booster website. Look in the tech section and they have a section on
trouble shooting the booster, mc etc. And yes that is the method
NCbird on the Coast of NC
"Dads Bird" for my father

Last edited by ncbird : 08-10-2011 at 10:29 PM.
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Old 08-10-2011, 11:31 PM
Astrowing Astrowing is offline
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  1. Your combination valve may have tripped shutting off fluid flow to the front or rear brakes. This condition will produce a very hard pedal. Check that fluid passes through the valve to both the front and rear by cracking a bleeder screw and observing a good flow of fluid. If one half of the system does hot have flow, re-center the valve.
  2. You may have frozen rear wheel cylinders or frozen caliper pistons. If these components freeze you can get a very hard pedal.
  3. Your pedal ratio may be too low. Check your pedal ratio. The pedal ratio must be in between 4:1 to 5:1. Some of the older cars that had power brakes used a ratio of almost 1:1. If you add a vacuum booster to this type of car you will have a very hard pedal. Typically we are talking about late 50's cars. Adjust ratio as necessary.
  4. Your booster may be undersized for the weight of the vehicle or the bore size of the master. If you try to use a small diameter booster such as a 7" street rod booster for a heavy car you will get a very hard pedal. Compounding the problem is an attempt to use a large bore master (1-114" or larger) on a small booster.

Above is from the MBM website. What is the pedal ratio of the Squarebirds as they are?

CLICK HERE for Jim's web site
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Old 08-11-2011, 12:32 AM
davidmij davidmij is offline
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Thx for the input guys, but if you go back throw this thread I completely eliminated the prop valve and ran just the front discs to a 3 way splitter and still had the same pedal and result. Plus my prop is not adjustable.
Each wheels cylinders and calipers work - I bled them and also looked at them moving one by one while my son stepped on the pedal. The guys at ABSpowerbrakes designed this cylinder and booster setup to work with 58-60 T-birds and have seen no failures (at least that's what they say).
However, I found this link with info about brakes. It describes what Dave Dare was explaining way back in the thread about the "throw" in the MC. I also talked to the guys at Brake Masters in Santa Fe. They said if the vacuum is at 13 I have plenty of vacuum. They also said that the pedal dropping while I step on it during start up is a good test and the booster is doing it's thing. They said I should check the throw in the MC. I'm going to try the directions in this link and see what happens this weekend.
Thx tons for the pointers and ideas!
regards, Dave J
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Old 08-11-2011, 12:33 AM
davidmij davidmij is offline
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Oh, and I'll definitely go to MBM's website and check out the info there.

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Old 08-12-2011, 11:33 PM
davidmij davidmij is offline
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Well, I dabbled a little with the booster pushrod adjustment - didn't really notice any difference. Then I was backing out of my driveway for a test run, I had put the car in neutral because it was almost stalling while in gear. I hit the brake hard and it jerked to a stop. When I drove down the street I shifted to neutral and hit the brakes, I got a chirp out of the tires. Seems that the vacuum must be dropping way low when I put it in gear, when I put it in neutral it works a lot better. I read that a poor engine can loose vacuum while under load, but can it be enough to make the booster perform that poorly?

- Dave
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Old 08-13-2011, 01:50 AM
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scumdog scumdog is offline
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Maybe, just maybe you might have to run the hose between the manifold and the booster through a vacuum can of some sort?

But it must be one hell of a tired motor (or have a really hot cam) if it has that little vacuum!!!

Has it got enough initial timing advance on the distributor? Not enough advance can cause a low vacuum.
A Thunderbirder from the Land of the Long White Cloud.
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Old 08-13-2011, 09:14 AM
REM REM is offline
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There should be a check valve in the supply line to the booster to let the booster hold high vac if the manifold vac drops. It should be good for at least one brake application. A vac cannister in-line would give even more reserve.
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Old 08-13-2011, 10:26 AM
davidmij davidmij is offline
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Yes, I do have the original booster in place with the 3 way valve. If I leave the car a day or two, then pull the hose off the booster it makes a strong, long whoosh as it sucks in air. I can even put my finger over the end of the hose and plug it as it's pulling air in. Hence it's working well, and sealing well.
It IS a very tired motor. It sat for 15 years and then the owner would start it (try to start it) with the 15 year old gas that looked like brown ale. The cylinders must have been bone dry.
I also read that the timing advance is important, it definitely needs to be looked at. I don't really know how to set it but the manual will tell me.
When I come to a stop and then start to accelerate the engine flutters (even stalled once or twice) I believe that's a timing issue maybe??? Yes, no?
thx again for the help.
- Dave J
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