Dual diaphragm booster of woes.

Boydsdodge

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So I had my dual booster rebuilt this winter on Tux this winter,. I still have no brake assist after replacing calipers, wheel cylinders, master cylinder twice, flex lines front and rear, new pads and shoes.
Booster passes the vacuum test, and the slight pedal fall when started. Holds 22" vacuum from engine and my vacuum pump.
I am stumped. Why I have come here to ask if anyone has had this problem?
Could it be that half the dual diaphragm id only working and thats why I get good vacuum readings but the other half is not working?
Pedal is very hard, almost feels like it is pushing back on me, sitting at a stop it will start to creep on idle making me use two feet at times. The car hasn't and can't be used in this state.
I am starting to panic because Carlisle is coming up fast. I have other issues I am working on, but this is really taking time.
Thanks.
 

Boydsdodge

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Two new masters,. and now back to the original. I have had bad new master on a past project, but this aint it.
 

Big_John

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I think I would look at push rod protrusion. There's a spec with an illustration in your FSM, but it boils down to the pushrod should be just a c hair short of touching the piston in the master cylinder.
 

Boydsdodge

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I thought and checked that, maybe a messed up. Would the pushrod with too much preload on the master cylinder cause this problem?
I will pull it and check now.
 

Boydsdodge

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Removed master from booster, checked depth of push rod, might have been tight at zero play, backed it of 2.5 turns. just went for drive, still same pedal, only with more free play in pedal before contacting master.
One of the symptoms is making me excited that I cured the problem, because at first it feels as it should, but two brake pushes later it is getting firmer and then hard by the time I go around a city block.
 

1970FuryConv

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Brake vacuum hose can collapse especially if it's fuel hose that is made for pressure, not vacuum.
Brake check valve: if you remove and blow at the hose fitting and air comes out the diaphragm side, you have a bad check valve.
If neither applies
1 You've gone thru 3 masters so that's not the problem.
2 You can WITH ENGINE OFF pump the brake pedal until all the vacuum is out of the booster and pedal is hard, then hold moderate pressure on the pedal, then start the engine. If you get a small amount of pedal drop, that's a good sign. If you get no pedal drop, that points to a bad booster.
 

PH27L7

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You've pretty much eliminated the hydraulic end of it so it's either some lack of vacuum or a defective booster rebuild. If you're lucky it might be a collapsing or plugged vacuum hose or some problem with the check valve. If it's the booster then you will unlikely be taking it to Carlisle. You could bench test the booster & see if the problem could be duplicated but removing & installing is a bit of a pain as you know.
 

Davea Lux

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Also check the fitting that comes out of the manifold to the booster, sometimes on moonshine blend fuels this fitting will carbon up and block vacuum to the booster. Otherwise, you probably have a defective booster..

Dave
 

Sixpactogo

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I thought and checked that, maybe a messed up. Would the pushrod with too much preload on the master cylinder cause this problem?
I will pull it and check now.
Too much pre-load would cause just the opposite. The brakes wouldn't release all the way causing warped rotors and drums. You went the wrong way by backing off 2.5 turns. It may have been set right if it was at zero play. I suspect your booster is not up to the task. Are you sure it is a dual diaphragm? How bout some pics?
 

Boydsdodge

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1973 Imperial dual diaphragm original booster rebuilt Jan 22.
I know I have too much play in pedal now, I had it correct. But to please the frustrated mind, I backed it off to be sure.

126F9D55-81F6-4CF4-9E8E-96E26B4C84B2.jpeg


853F8E08-3667-4B61-A55D-CE2B913C4ED9.jpeg


0AE6EF33-6402-4BA1-B1AB-C929F8954E77.jpeg
 

Sixpactogo

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The booster looks correct and nicely done. Still seems like it is not up to the task though like it is losing vacuum somehow.
 

HWYCRZR

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For Sh!ts and giggles have you unplugged and capped your cruise control vacuum to make sure that system isn’t causing issues?
Not allowing full vacuum to the booster? As as said above blow through your check valve to make sure it is working.
 

Boydsdodge

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For Sh!ts and giggles have you unplugged and capped your cruise control vacuum to make sure that system isn’t causing issues?
Not allowing full vacuum to the booster? As as said above blow through your check valve to make sure it is working.
Yes I have checked the cruise, I have checked the valve, it felt a little restricted so I replaced it with another. I am waiting on a reply from the rebuilder. I wrote the rebuilder on Thursday, I haven't received a reply yet.
 

Charlie1961

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So I had my dual booster rebuilt this winter on Tux this winter,. I still have no brake assist after replacing calipers, wheel cylinders, master cylinder twice, flex lines front and rear, new pads and shoes.
Booster passes the vacuum test, and the slight pedal fall when started. Holds 22" vacuum from engine and my vacuum pump.
I am stumped. Why I have come here to ask if anyone has had this problem?
Could it be that half the dual diaphragm id only working and thats why I get good vacuum readings but the other half is not working?
Pedal is very hard, almost feels like it is pushing back on me, sitting at a stop it will start to creep on idle making me use two feet at times. The car hasn't and can't be used in this state.
I am starting to panic because Carlisle is coming up fast. I have other issues I am working on, but this is really taking time.
Thanks.
I had a similar problem on my 66 Fury, I called The Ram Man and he suggested that I do a field test so I could see with my own eyes whether or not it was working. He has several videos about testing boosters after removing it from the car and having it isolated from other potential issues. He told me to test it before I wasted any money on shipping it to him for a rebuild. He also said to only ship the booster for a rebuild if it failed the test.


I hope this helps you, I completely understand because I had a similar disaster and tried to fix it myself with no success.
 

1970FuryConv

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I had a similar problem on my 66 Fury, I called The Ram Man and he suggested that I do a field test so I could see with my own eyes whether or not it was working. He has several videos about testing boosters after removing it from the car and having it isolated from other potential issues. He told me to test it before I wasted any money on shipping it to him for a rebuild. He also said to only ship the booster for a rebuild if it failed the test.


I hope this helps you, I completely understand because I had a similar disaster and tried to fix it myself with no success.

Thanks Charlie.
Informative video on bench testing a booster!
 

TheRamManINC

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So I had my dual booster rebuilt this winter on Tux this winter,. I still have no brake assist after replacing calipers, wheel cylinders, master cylinder twice, flex lines front and rear, new pads and shoes.
Booster passes the vacuum test, and the slight pedal fall when started. Holds 22" vacuum from engine and my vacuum pump.
I am stumped. Why I have come here to ask if anyone has had this problem?
Could it be that half the dual diaphragm id only working and thats why I get good vacuum readings but the other half is not working?
Pedal is very hard, almost feels like it is pushing back on me, sitting at a stop it will start to creep on idle making me use two feet at times. The car hasn't and can't be used in this state.
I am starting to panic because Carlisle is coming up fast. I have other issues I am working on, but this is really taking time.
Thanks.
Do not believe me ….call ANY legit REBUILDER
 
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