Hello all,

One of the few deviations from stock that I made on my 56 Merc as I restored it was to add a dual master cylinder with a 7" dual diaphragm power booster. The car is just recently completed but in moving it around I find that the brake pedal has little travel and is rock hard. That's all good but the car stops poorly and the pedal does not feel "boosted" at all.

All brake components are new, the engine makes good vacuum. The vacuum source for the booster is the nipple at the base of the carb facing to the rear and I have used 1/2" hose to connect to the booster. The valve that the hose hooks to on the booster works correctly .

I was wondering if an incorrectly adjusted push rod (between booster and master) could cause this conditions ? Any ideas or thoughts are welcome.

Pete

First of all, vacuum should be manifold vacuum, not venturi(carb) vacuum. Different type of signal. Secondly, do you have play in the rod going from off the brake pedal to the booster.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Is the booster setup new or used?What are you using as a pushrod-an adjustable length one or the stock one?As Paul mentioned you need manifold vacuum.If there is no outlet on the manifold for a fitting you may have to drill and tap for one.It sounds like you are getting no "power boost" for sure.Power brakes with non functioning booster will give a harder pedal than the non boost original setup.One more question would be are the wheel cylinders moving freely(not stuck seized?)

  

 I will reattach the hose to manifold vacuum to see if it makes a difference. The vacuum at the large port at the rear of my Holley 1850 is full time not ported but I take it that there is not enough volume at that location to operate the brakes?

These are all new parts ( booster and master) and the push rod is adjustable.

There is play between the brake pedal and the booster

And you are correct the pedal feels no different with the car running than when it is not as in no boost

If you have a fulltime vacuum source the booster should work.Have you tried adjusting the pushrod longer so there is less freeplay?My friend with a 54 Mercury added the booster kit to his and couldnt get it to work properly.After playing with the length of the pushrod and gradually making it longer he got it working properly.I assume there is a check valve on yours where the vacuum hose attaches to the booster?I have installed a similar dual master and booster( and disc brakes) on mine as part of my winter project.I have bled the brakes but because the motor is out I have not been able to see how this new setup works.I have added an adjustable proportioning valve and I know once I get it running I will have to spend some time sorting out the booster setup and adjusting the brakes.One last suggestion regarding your booster-it is possible you have a defective unit.The guy I bought mine from in the US told me he had to replace one recently because it was defective out of the box.I dont know where you bought yours but i got mine from "the old irishmans auto" who sells these setups on Ebay.

  

I don't want to clog up the diagnostic conversation but my first question would be, were the brakes fully functional before the addition of the master cylinder/booster? If so, how much vacuum is your engine making at idle? Then, if the vacuum is adequate, is the power booster a used/new or rebuilt unit with a check valve?



Mark Hebard

57 Black Tbird 312/auto

Bingo, my set up came from oldIrishDave. I have been in touch with him and it is he that suggested push rod length. To me it feel like a dead booster.

The pedal feels like a block of wood, otherwise the brakes work just fine

OK So try that and let me know if that solves the problem.Might help me get mine setup better when the time comes.One thing I did on mine that you might consider doing.I drilled a second hole in the pedal about an inch lower than the stock one which lowers the pushrod end and makes it straighter going into the booster.I find the angle of the pushrod almost rubs on the firewall installed as is without the second hole.I also used a rubber floorplug from Dennis Carpenter which is exactly the right size for the hole in the firewall.Cut a hole in the centre and cut some slots radiating out from the centre.The pushrod goes through it and it provides at least some sealing rather than just having a hole there.

  

Hi Guys; Glad this came up. I'm looking to replace my old original master cylinder to a double pump master cylinder. Can anyone tell me what would be the best? I won't be using any booster, just the basics, and does the front valve go to the front brakes and the rear to the rear? Advanced thanks.

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Old Y Block

Be sure and check for vacuum leaks. I have a friend that just had the same problem, was missing the rubber cap from one of the vacuum ports. Replaced the cap and problem was gone. I used the same booster from old Irishman's and it works great. Mike

http://www.y-blocksforever.com/forums/Topic37961-3-1.aspx?Highlight=brakes

1956 Fairlane Victoria (ORREO)

 

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