Hey everyone. So I've been doing some brake diagnosis with my 64 Dynamic. Since iv owned the car the pedal feels "werid". It's pretty much no brakes until it's about 70 % down the pedal then it's almost full lock. Extremely sensitive too
-I first went to the booster push rod length and with an adjustment, it didn't fix it. NOTE: If I adjust the push rod out farther, it does the same thing but at the bottom of the pedal, it does fully stop the car
-then I thought maybe it's the booster itself, but after unplugging it, it does the same thing, just requiring more effort to push obviously
- then I took each drum off and inspected the brakes, the fronts were in good shape, so I justed cleaned and regressed the adjusters and adjusted the shoes when the drums went back on. The rear though are a different story, driver rear was destroyed behind the drum. All the hardware was missing and wheel cylinder had a very bad leak. So I fully replaced all components on both rear brakes and bled them good. Still even after new rear brakes and good front ones, the issue still exists.

This car is 4 wheel drum.

Im guessing the only remaining component that could cause this is the master Cylinder. It was upgraded years ago to a dual circuit system.

What are your guys thoughts?

 

Alex, post some pictures of the dual master cylinder and piping so we can get an idea how it was done.

You may already know both Moraine and Bendix power boosters and m/c's were used on the 64 full-size cars, and they don't interchange. If the dual m/c and booster aren't compatible that may be contributing to the weird brake pedal feeling. I know a lot of people use a 1966 Cadillac m/c when making this conversion but I think all Cadillac used Moraine boosters.

Joe P will have insight.

 

Here a picture:

 

The white thing on the front of the booster is a vacuum check valve.
It should be connected via a hose to the intake manifold.
Otherwise the booster gets no vacuum.

 

^^x2^^
As Charlie pointed out - you have no vacuum being delivered to your brake booster and therefore you have no "power" (assist) brakes; albeit, the reason your brakes feel so "weird" is because you have brakes but no power (assist) via the brake booster (which is the purpose of the brake booster). It would be in your best interest (viewing the condition of the brake booster check valve and its orientation (opening facing upwards) to install a new brake booster check valve & grommet when you eventually do hook up the vacuum.

 

I had said in the starting post that I tried with the booster plugged into vaccum and without to see if there is a different and there is not
​​​something to also note, when I remove the master I hear a "hiss" noise like all the vacuum has left the booster. Not sure where its coming from but it's when I fully detach the master from the booster

 

Fair point - I guess I was not clear on exactly what you meant by...
...we have many levels of users and it's not always clear exactly what a user means....again, fair point, you didn't state you removed the vacuum hose from the brake booster...you said you unplugged (something)...sounds picky maybe, but....

 

Again, only trying our best to assist you, the above statement is NOT what was stated in your first post (to be clear)...the above statement is FAR more meaningful when you (finally) have stated with the booster plugged into vacuum.

 

If you hear a hissing, and you're positive it's coming from the brake booster it's most likely the booster diaphragm has failed allowing air to escape. It's most likely going to be one of three items if it's hissing at you:
Booster diaphragm, master cylinder gasket, or vacuum hose (possibly at the check valve) or the hose itself.

 

Perform this test (there are many videos covering a leaking brake booster), this guy does a pretty nice job.

 

That's a Bendix booster. If that's a Moraine master cylinder it's probably not completely compatible with it. Difference in pushrod lengths etc.

Sounds like that booster needs a rebuild anyway.

 

I saw that and knew what you were saying.

The "hiss", is this with the engine not running and you are separating the Master cylinder from the power brake booster ?

 

Yes, like the rubber o ring thing around the pushrod. But again this issue happens with the boost unplugged from vaccum too.
if the booster is at fault, Are there are units that could be compatible? I saw another use on a different form use one from a kia

 

Just so I'm clear on the actual symptoms, what you are saying is that when you press the pedal (with booster vacuum or not) you get no resistance until the pedal is nearly to the floor, then the brakes lock up? Are you sure that all four wheels are engaging? Depending on the speed, one wheel will stop the car.

The dual circuit M/C that was installed is not the Cadillac unit that I normally recommend (the Caddy M/C has the outlet ports on the engine side). This naturally begs the question of which M/C you have, which booster you have, and which pushrod is between them. Did you install the M/C or did someone else? The only way to know for sure is to disassemble the M/C from the booster and take pictures of the front face of the booster and the back of the M/C. Also note that overadjusting the pushrod is just as bad as having it too short. If the pushrod is too long the M/C pistons will never retract far enough to uncover the compensating port in the M/C that allows fluid from the reservoir to fill the system. I would suggest that you back off any adjustments and start again, making sure the piston is fully retracted when the pedal is released. And note that there is a rubber gasket between the M/C and the booster that seals the forward chamber of the booster. Removing the M/C when there is vacuum in the booster will always result in hissing. I'll also note that for "upgraded" parts, the booster and M/C look pretty shaky. How was the rest of the system plumbed? Was the 67-up distribution block used or just a tee fitting? And please tell me that there isn't any type of proportioning or combination valve used.

 

To try and answer all those questions:

- Your theory is correct, as my foot pushes down on the pedal, there is a very small amount of braking feeling but not much until about 80% of the pedal travel, then the car comes very quickly to abrupt stop. I also have to apply barley any force to move the pedal, insanely sensitive.
-I am positive the car is braking on all 4 wheels because as when i was bleeding, the drums would move or twitch. The stop (even though abrupt) feels good, like grabs the road hard
-The master was put on before I owned it. NOTE: when I bought the car, (before the body off frame resto) The cars brakes felt like the same weird feeling, so this feeling is not indicative of anything that may have been moved around during the resto. What's is incredibly strange too is the man before me drove that car all year with no issues with the brakes, then it sat for a few months and then I bought it.
-The front brakes are plumed with a tee fitting, same with the rear but The T fitting is above the axle, not near the master
-there is no proportioning or combination valve installed, this I understand for sure

THERE IS NO DIFFNECE WHEN THE VACCUM LINE IS CONECTED OR DISCONNECTED ON THE BRAKE BOOSTER!

 

We finally said screw it and rebuilt the master cylinder. After honing it and cleaning it extremely well, the rebuild didn't work and were back to sqaure one. We did not know where the master was from so we did not replace the cup seals, they were in good shape with no damage or tears. But were positive now its something with the master itself because the piston kept getting stuck in the bore before and after the rebuild. Also the fluid level was rising so far into the res, it was forcing fluid past the cap!! This could be why the pedal was acting so strange. I ordered a cheap Dorman master from AutoZone and we should be good to go!

I purchased a pushrod tool to wave a "out of adjusted" push rod coming from the booster

The master ended up being from a 67-69 Camaro.

 

Go back to the original m/c setup