Power brake booster problems ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

RShaips · 10-30-2004, 04:24 PM

I have a 67 SWB with power brakes that are not working properly. I have a rebuilt 383 Stroker motor and the complete truck has been redone. Now my problem is my brakes worked great but when I went to slam on the brakes they would take a litttle while to stop. I determined that my brake booster was leaking a little bit so I replaced it. Now my brakes feel like they are not power anymore, I have to stand on the pedal to make them stop quickly. Think I just got a bad booster or could there be another problem ? I have new wheel cylinders in the back and new brake lines throughout most of the truck. Seems like I have plenty of vacuum. Could the portioning valve cause this ? Thanks for the help.

norville · 10-30-2004, 04:35 PM

It sounds like the booster. Run the truck, shut it off, then crack the vac line at the booster should hear hiss.

Or after running shut off then pump brakes should be easy then hard. If no change propably bad booster if the vac is there.

I'm sure others will have better advice.

norv

RShaips · 10-30-2004, 05:23 PM

I tried it earlier, there was almost no difference with the truck off or running. Brake pedal is hard to push. I hate buying new parts that are bad !

RShaips · 10-31-2004, 10:24 AM

a little bump

Longhorn Man · 10-31-2004, 06:02 PM

how big a cam does that 383 have in it?
Did you replace the little check valve going into the booster?

Try rolling down the road at about 30 or so in first gear, lift off the gas and let the truck decelerate against the motor. Press the brakes. When decelerating, the engine is making more vacume than at any other point. This will make lots of vacume, and tell you if the new booster is junk or not.
Last test before removing the booster for replacement... Remove the large vac hose from the carb/intake. Clean it off real good, put it iin your mouth and suck real hard. (I'm asuming you don't have a hand held vacume pump w/guage) If air comes through the hose and continues to...then remove the booster and call the parts guy. (don't yell...he's your friend) If the hose seems to hold vacume, then the problem is the check valve or the engine not making enough vacume.
You could just ditch the booster. I don't have pwr brakes on the 69, and in all reality, I hardly miss it at all.

RShaips · 10-31-2004, 10:18 PM

The booster holds vacuum when I suck on the hose, where is the check valve you are talking about ? The brakes used to work great with this same motor so I think I have plenty of vacuum. I know that when I unplug the vacuum line to the booster my motor barely runs until I hook it back up. Thanks for the help

Longhorn Man · 10-31-2004, 10:22 PM

There should be a plastic elbow piece where the hose plugs onto on the booster.
I'll bet a punch in the gut that's what you need.
You verified that the booster is sealed...booster is OK
The engine runs like crap when you unplug the hose...verified that the hose doesn't have a leak (or not much of one)
It all worked with the engine set up the same way before... the cam is not to blame.
About the only thing left is the check valve.

RShaips · 11-01-2004, 09:56 PM

When I removed my check valve the booster still was holding pressure from yesterday when it ran. The valve is new and seems fine. My brake pedal feels almost the same when it is running or not, very hard to push. Any more suggestions. Thanks

Longhorn Man · 11-01-2004, 09:59 PM

Does it make a hissing noise when you hit the brake pedal?
Does the idle chainge when you hit the pedal?
This is friggen weird

RShaips · 11-01-2004, 10:05 PM

Idle does not change, no hissing noise.Everything seems fine except it doesn't stop unless you have a strong leg, I am 6'4" 235# and I have to stomp on it.They worked nice before the new booster its just that they would'nt stop quickly, and you could hear a hissing sound so I replaced the booster . Now they feel hard as a rock !

Longhorn Man · 11-01-2004, 10:12 PM

Any chance you hooked the rod to the wrong hole on the brake pedal?

RShaips · 11-01-2004, 10:23 PM

No, I didn't even unhook it from the brake pedal until after I changed it. Then I tried adjusting it in and out to see if maybe I could get more leverage to make it easier to push, but no luck. What about the portioning unit, its about the only thing that I have not replaced ?

sam's 72 · 11-02-2004, 12:09 AM

Keeping this at the top. I have the exact same problem. I have a 72, every thing new on the brakes, new booster, new master cylinder, new proportion valve, all new lines, new calibers, new wheel cylinders, new hoses to calibers, every single part has beew replaced new, and I still have this same problem.
Sam

Longhorn Man · 11-02-2004, 12:19 AM

dayum

Jason71k10 · 11-02-2004, 11:22 AM

ttt, i'm curious about this one too

curbyk · 11-02-2004, 04:02 PM

this may not have any value but...is the size of the diafram the same on the old as the new, may not have the same assist.

RShaips · 11-03-2004, 12:17 PM

Not sure on the diafram, All I know is that my brakes don't really change in how they feel with the motor on or off. I think I will buy another booster and see what happens.

10-30-2004, 04:24 PM	#1
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	Power brake booster problems ? I have a 67 SWB with power brakes that are not working properly. I have a rebuilt 383 Stroker motor and the complete truck has been redone. Now my problem is my brakes worked great but when I went to slam on the brakes they would take a litttle while to stop. I determined that my brake booster was leaking a little bit so I replaced it. Now my brakes feel like they are not power anymore, I have to stand on the pedal to make them stop quickly. Think I just got a bad booster or could there be another problem ? I have new wheel cylinders in the back and new brake lines throughout most of the truck. Seems like I have plenty of vacuum. Could the portioning valve cause this ? Thanks for the help.

10-30-2004, 04:35 PM	#2
norville Senior Member Join Date: Jun 2004 Location: Mountain Top, Pa Posts: 323	It sounds like the booster. Run the truck, shut it off, then crack the vac line at the booster should hear hiss. Or after running shut off then pump brakes should be easy then hard. If no change propably bad booster if the vac is there. I'm sure others will have better advice. norv __________________ 1986 C10 Scottsdale 5.3, TH400

11-02-2004, 12:09 AM	#13
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	Keeping this at the top. I have the exact same problem. I have a 72, every thing new on the brakes, new booster, new master cylinder, new proportion valve, all new lines, new calibers, new wheel cylinders, new hoses to calibers, every single part has beew replaced new, and I still have this same problem. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

11-02-2004, 11:22 AM	#15
Jason71k10 ready for reassembly Join Date: Jun 2002 Location: Barrie ONT, Canada Posts: 413	ttt, i'm curious about this one too __________________ stock 71 4x4 2003 Jeep Liberty, rocky mountain edition I'm obsessed, and wouldn't have it any other way!

11-02-2004, 04:02 PM	#16
curbyk 69 C-10 project Join Date: Sep 2004 Location: Eastern, NC Posts: 184	this may not have any value but...is the size of the diafram the same on the old as the new, may not have the same assist. __________________ 69 C-10 Work is complete

10-30-2004, 05:23 PM	#3
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	I tried it earlier, there was almost no difference with the truck off or running. Brake pedal is hard to push. I hate buying new parts that are bad !

10-31-2004, 10:24 AM	#4
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	a little bump

10-31-2004, 06:02 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	how big a cam does that 383 have in it? Did you replace the little check valve going into the booster? Try rolling down the road at about 30 or so in first gear, lift off the gas and let the truck decelerate against the motor. Press the brakes. When decelerating, the engine is making more vacume than at any other point. This will make lots of vacume, and tell you if the new booster is junk or not. Last test before removing the booster for replacement... Remove the large vac hose from the carb/intake. Clean it off real good, put it iin your mouth and suck real hard. (I'm asuming you don't have a hand held vacume pump w/guage) If air comes through the hose and continues to...then remove the booster and call the parts guy. (don't yell...he's your friend) If the hose seems to hold vacume, then the problem is the check valve or the engine not making enough vacume. You could just ditch the booster. I don't have pwr brakes on the 69, and in all reality, I hardly miss it at all.

10-31-2004, 10:18 PM	#6
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	The booster holds vacuum when I suck on the hose, where is the check valve you are talking about ? The brakes used to work great with this same motor so I think I have plenty of vacuum. I know that when I unplug the vacuum line to the booster my motor barely runs until I hook it back up. Thanks for the help

10-31-2004, 10:22 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	There should be a plastic elbow piece where the hose plugs onto on the booster. I'll bet a punch in the gut that's what you need. You verified that the booster is sealed...booster is OK The engine runs like crap when you unplug the hose...verified that the hose doesn't have a leak (or not much of one) It all worked with the engine set up the same way before... the cam is not to blame. About the only thing left is the check valve.

11-01-2004, 09:56 PM	#8
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	When I removed my check valve the booster still was holding pressure from yesterday when it ran. The valve is new and seems fine. My brake pedal feels almost the same when it is running or not, very hard to push. Any more suggestions. Thanks

11-01-2004, 09:59 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Does it make a hissing noise when you hit the brake pedal? Does the idle chainge when you hit the pedal? This is friggen weird

11-01-2004, 10:05 PM	#10
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	Idle does not change, no hissing noise.Everything seems fine except it doesn't stop unless you have a strong leg, I am 6'4" 235# and I have to stomp on it.They worked nice before the new booster its just that they would'nt stop quickly, and you could hear a hissing sound so I replaced the booster . Now they feel hard as a rock !

11-01-2004, 10:12 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Any chance you hooked the rod to the wrong hole on the brake pedal?

11-01-2004, 10:23 PM	#12
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	No, I didn't even unhook it from the brake pedal until after I changed it. Then I tried adjusting it in and out to see if maybe I could get more leverage to make it easier to push, but no luck. What about the portioning unit, its about the only thing that I have not replaced ?



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11-02-2004, 12:19 AM	#14
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	dayum

11-03-2004, 12:17 PM	#17
RShaips Senior Member Join Date: Jun 2002 Location: Augusta Missouri Posts: 804	Not sure on the diafram, All I know is that my brakes don't really change in how they feel with the motor on or off. I think I will buy another booster and see what happens.

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