POWER BRAKE VACUUM

-
WAYNE0

WAYNE0

Well-Known Member
Joined
Oct 16, 2019
Messages
918
Reaction score
881
Location
milton pa.
Where and how do you test to see how much vacuum you have for power brakes ? My car came with manual and i want to add power brakes. The engine is a 360 397 ci. I dont know cam specs. What all do i need to change. The picture is what i have now. The carb is a demon on a eddy aluminum intake.

MASTERCYLINDER BRACKET 004.JPG
 
Should be a fitting in the intake somewhere behind the carburetor.
 
A vacuum booster will have a large hose attached to full manifold vacuum. You will need at least 10 inches of vacuum.
 
And the hose is Made for Vacuum. 11/32 ID I believe. As far as vacuum measurement, any non ported nipple you can get the reading from, will be the same
 
Save yourself the problems and diagnose why you think you need power brakes.

MC piston dia can change the feel.

Diferent pads can change the feel.

I have a 67 dart convertible, in the 3100 lb range.

Front KH disk and 10x1.75 rear drum manual brakes, stock MC piston size, Stops just fine.

They can be locked up in a panick stop situation if need be.
 
I have 4 wheel disk brakes and it just have a good feel. spongy and have to pump the pedal ive bled them several times
 
Easy fix, put the rear drum brakes back on. The rear brakes only do app. 20% of your braking.
Disc will only be better when they are wet over drum's. Otherwise unless you're regularly towing, live in the mountains and ride the brakes down, or make lots of high speed stops, you will never need the disc on the rear.
More eye candy than practical.
 
A Booster is not gonna solve spongy.
Spongy can be :
Air
hoses
Plumbed backwards at the Combination-valve
calipers not aligned with disc
pads; bent, twisted, flexing,

Do yourself a big big favor;
Get all the calipers off the brackets, and clamp each piston into the bottom of the caliper bore with a big sturdy C-clamp; Be careful as this can overfill the reservoir as the fluid backs up; you might have to take some out. Yes there are alternatives but I won't recommend them, this late in the game.
This eliminates everything but air and hose flex, so if you got all the air out, after a pump or two, your pedal will now be hard and high and stay high.
> if the pedal will not come up high, then the compensating port is not working
>If the pedal slowly falls under your foot at moderate pressure, with NO visible external leaks, the master is bypassing internally and needs to come apart.
>If the pedal is mildly spongy, check for flex-hose movement; a little swelling is normal; it should be just barely perceptible
>>If after eliminating all of the above, and she is still spongy and your C-clamps are sturdy, then; sorry man you still got air.

Did you bench bleed the M/C?
 
Last edited:
MoparLeo said:
Easy fix, put the rear drum brakes back on. The rear brakes only do app. 20% of your braking.
Disc will only be better when they are wet over drum's. Otherwise unless you're regularly towing, live in the mountains and ride the brakes down, or make lots of high speed stops, you will never need the disc on the rear.
More eye candy than practical.
Click to expand...
I used the rear disk kit because ive had it for several year. I bought it for a past build that i never used it on. It was cheaper to use it than buy all new rear drum brakes system. The car was a manual 4 drum car. With automatic. I changed it to a 4spd. I used the original brake pedal push rod and brass brake block
 
Last edited:
Are your rear disks adjusted correctly?

Some systems have a unique adjusting procedure due to the e brake.
 
ARE THE BLEEDERS AT THE TOPS OF THE CALIPERS?

I ran a Versailles rear axle (Ford 9, factory dsk) and 73/4 A body disks up front. Pedal was rock hard about 1/2 way travel and stopped like droppin a brick on pavement. NOT spongy.
 
67Dart273 said:
ARE THE BLEEDERS AT THE TOPS OF THE CALIPERS?

I ran a Versailles rear axle (Ford 9, factory dsk) and 73/4 A body disks up front. Pedal was rock hard about 1/2 way travel and stopped like droppin a brick on pavement. NOT spongy.
Click to expand...
yep
 
they seam to be when i have someone pump the brakes and hold them you cant turn the rear wheels
Dana67Dart said:
Are your rear disks adjusted correctly?

Some systems have a unique adjusting procedure due to the e brake.
Click to expand...
 
WAYNE0 said:
they seam to be when i have someone pump the brakes and hold them you cant turn the rear wheels
Click to expand...
When you say pump the brakes you mean they press the pedel more than once to achieve the pressure?
 
To rule out the rear brakes...

Disconnect the rear line at the distro block.

Put a plug in the distro block port. Bleed the brakes, crack the plug open to bleed the rear system as if it was a caliper.

Protect the rear line so it does not leak fluid, An appropriate cap or baggy tapped to the line etc. To keep fluid from hurting your paint etc.


you will only have front brakes, but if they and the master are blead correctly and in propper working order you should have a firm pedal feel no pumping needed.

Do the same with the front brakes. If the rears feel spongy then you know where your problem is.
 
WAYNE0 said:
yes
Click to expand...
Not the way to test brakes.

If the brake needs to be pumped up to hold, the pad is too far away from the disk. The pad should be skimming the disk at all times. If you spin the wheel you should hear scuffing of the pad.

My money is on the rear disks being not adjusted propperly.



When you test the brakes...

Get all 4 wheels up in the air.
Apply the brakes, 1 pedal press and release.
Rotate the front wheels and listen for scuffing.
Rotate the rears and listen for scuffing
Make note of what you hear.

Have helper apply the brakes (single press) and hold, no need to stand on the pedal.

You go out and attempt to rotate each wheel. Note your findings.


This is a prime example of:
"The parts you don't add, don't cause you no problem"

And

KISS " Keep it simple stupid"
 
Last edited:
You must log in or register to reply here.
-

Back
Top