Brake booster going out?

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72Ruster

72Ruster

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Hey all, just wanted to make sure I'm on the right track before I buy any parts. Car is a 72 Duster, 318 3-speed manual with front Kelsey-Hayes disks and rear drums.

The issue: power brakes are pretty much gone. Ton of pedal pressure to get the car to stop. Replaced the vacuum hose to the intake cause it was pretty old. Issue persisted. Checked vacuum at engine and its 19-20in at idle so plenty. When I press the brake in I can hear it hissing and releasing pressure. It also doesn't seem to return the pedal as high as it used to. If I park in my slanted driveway the brake lights will usually stay on because Im holding the brake when I turn the car off. The car immediately loses brake pressure when it turns off. It will immediately roll back the instant it loses vacuum.

The engine speed also increases significantly when the brake is pressed. Probably 3-400 RPM. Dont have a tach so dont know exactly though

Is there anything else I should check before I order up a new booster? It's pretty rusty, the rear rod cover is shredded and it already has a remanufacutred sticker on it so not worth rebuilding again. Has anyone used the right stuff 8" booster from Jegs or anywhere? Thanks in advance.

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you can try replacing the check valve and seal at the booster where the hose connects, but dang, that's rusty :)
 
I agree withe the gasket and check valve.

You could check with a vacuum pump on the existing parts. If it doesn't hold a vacuum the parts above are cheap.

You could also get a one port check valve
 
kursplat said:
i'll wait here...
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Not as many holes elsewhere, but it looks to have sat in a field or something for a looooong time. The bottom of the dash is rusted pretty good. Not really sure how it happened. The channel underneath is fine, but the bottom (visible part) has been eaten through and is flaky in some spots.

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Dana67Dart said:
I agree withe the gasket and check valve.

You could check with a vacuum pump on the existing parts. If it doesn't hold a vacuum the parts above are cheap.

You could also get a one port check valve
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Yeah I'm not sure why it has so many ports. The connector on the intake is a monstrosity with the brake booster and like 5 (!!!) vacuum ports. All are plugged with new nylon caps.
 
kursplat said:
you could also go manual and never deal with this again :thumbsup:
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Id really like to but every thread people seem to have problems with the rod. Its my daily driver and only vehicle so I like to know when I take something apart its going to work again lol. The space it saves alone is worth it to me
 
72Ruster said:
Id really like to but every thread people seem to have problems with the rod. Its my daily driver and only vehicle so I like to know when I take something apart its going to work again lol. The space it saves alone is worth it to me
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Dr Diff, no problems. i don't even redo the lines, just gently push the MC into position so they don't kink.
 
You can verify the check valve works by blowing into it, you should not be able to. Once you verify, or replace, the check valve you can check the booster by stepping on the brake pedal with the engine off, start the engine and the pedal should drop a bit. No drop indicates the booster is bad.
 
I would suggest separating the MC from the booster and take a look at the booster. You just might have a leaking MC if you find fluid in the booster. Just a quick elimination of a leaking MC.
 
72Ruster said:
Not as many holes elsewhere, but it looks to have sat in a field or something for a looooong time. The bottom of the dash is rusted pretty good. Not really sure how it happened. The channel underneath is fine, but the bottom (visible part) has been eaten through and is flaky in some spots.

View attachment 1715559802
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And, speaking of 'flakey' - - (no, NOT the owner- :p) - - I cringe every time I see a bumper with the failing chrome pieces - as sharp as razor blades - and how many times I sliced open a part of my hand. Lesson learned. :(
 
AJ/FormS said:
If you hear hissing during pedal application, then the unit is defective, and the rise in rpm proves it, as the engine is sucking bypass air.
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Yeah i kind of figured :( Wanted to ask first as I have a bad habit of buying the wrong parts. Thank you!
 
hwd2 said:
And, speaking of 'flakey' - - (no, NOT the owner- :p) - - I cringe every time I see a bumper with the failing chrome pieces - as sharp as razor blades - and how many times I sliced open a part of my hand. Lesson learned. :(
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I've got a not-peeling one I need to throw on. Got a decent ding in the side where it wraps around the body I'm trying to hammer out with poor results.
 
kursplat said:
Dr Diff, no problems. i don't even redo the lines, just gently push the MC into position so they don't kink.
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So Im 90 percent sure I ordered the wrong booster and want to just go to manual brakes. Which master cylinder should I use for going that route? Will I just need the pushrod and master?

Also I had started to tear down the booster before the new one arrived. How the hell do you get the pushrod off the pedal? Its just spinning and doesn't seem to be any way to get a hold of the back bolt. Thanks in advance.
 
reuse the master cylinder you have as long as there isn't anything wrong with it. might be easier to pull the front seat to get the bolt. you're going to need a manual push rod and the rubber grommet to hold it in place. you can get a used one or go new. @DoctorDiff has both. where about's in "cali" are you?
 
kursplat said:
reuse the master cylinder you have as long as there isn't anything wrong with it. might be easier to pull the front seat to get the bolt. you're going to need a manual push rod and the rubber grommet to hold it in place. you can get a used one or go new. @DoctorDiff has both. where about's in "cali" are you?
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Wouldn't the power brake master that's on there be a super firm pedal? That's essentially what Im pushing on with no power brakes right now lol. I'm up near the Bay area. Do you have a photo of the bent lines? Seems like they'd be way too long to not kink somewhere.
 
the peddle is firm, but nothing like with a broken booster. i'm not home but here's a pic from another thread i had. this was a 74' that had power brakes. just removed the booster and gently moved the MC into position. no need to open the lines up, just don't kink the lines
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kursplat said:
the peddle is firm, but nothing like with a broken booster. i'm not home but here's a pic from another thread i had. this was a 74' that had power brakes. just removed the booster and gently moved the MC into position. no need to open the lines up, just don't kink the lines
View attachment 1715562962
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Thanks a ton. I'm going to grab a new Master just because mines so crusty. Might order the lines just in case cause theyre a bit rusty too.
 
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