vacuum problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

greasemonkey · 09-10-2004, 11:49 AM

I upgraded to power brakes, and I think I have a problem with my vacuum. I have adjusted the carb (Edelbrock 1406) to get the highest possible reading, about 16.5-17" at the most at idle. Classic Performance says I need at least 18" to work properly. I am pretty sure all the lines are properly sealed.
When I hit the brake, the vacuum drops about 3-4" and then regains as I hold the brake. When I release the brake, the vacuum drops about 5" and then rises again. At slow speeds, the brakes work really well, but at speeds above 35 or so, they don't work so well. They apply, but it doesn't stop fast. It will start to slow, then the pedal gets really hard and I can't stop any faster. I used to be able to lock up my old manual drums, but these power discs don't slow very well at all. Sometimes they stick too, and drag just slightly. If I pump the pedal a couple times, they will un-stick themselves.
Is all this a sign of poor vacuum, vacuum leak, or something else? I have the original quadrajet intake, and I have heard that I should use the port on it instead of the one on the carb. How do I do this?
Thanks,
John

Gary · 09-10-2004, 12:09 PM

I have power brakes too and this sounds almost exactly how my brakes are.

The shop I took it too put a big PVC cannister by the brake booster as a vacuum boost I suppose but it still won't "lock" the tires if I hit the brakes hard.

I'm having a new intake and carb installed wonder if that will change the available vacuum at all?

Longhorn Man · 09-10-2004, 12:16 PM

When I had the first Longhorn, it had power brakes, and when I installed my cammed out 350 in there, vac was in the single digits. I installed a vacume can from jegs and then my brakes worked fine. Well, almost fine. in bumper to bumper traffic, after hitting the brakes and then idling forward, then brake then creep then brake again...that 3rd hit was the last of the vacume assist, and the 4th one with the rock hard pedal would always induce panic. Since an engine naturally makes more vacume in deceleration mode than idle, steady RPM or even revving it up, all you have to do is pop it in neutral and rev it once or twice to 2000 or 2500 RPM.

Gary · 09-12-2004, 04:51 AM

So basically these "vacuum canisters" do the same thing that bigass pvc contraption they put on my system does?

jhow66 · 09-12-2004, 01:06 PM

Does your brake petal set close to the floor? If so adjust the rod under dash to bring petal up higher. When sdjusted right the petal arm will be in contact with the rubber bumper on bracket. If you run out of adjustment before it reaches bumper you have the wrong adjustment rod--either get one for power brakes or cut into and weld a piece in (this is what I did). This worked for me as I had the same problem(no stopping power). The differance was like going from a 20 oz. hammer to a 10 lb. sledge hammer. Stops with a touch of the toe. It all comes down to leverage.

Longhorn Man · 09-12-2004, 07:43 PM

Quote:

Originally Posted by Dixiesys

So basically these "vacuum canisters" do the same thing that bigass pvc contraption they put on my system does?

Are you refering to the check valve that is plugged into the booster?
If so, then yes. You will also need one of these on the canister.
I have one here I can ship you for 15 bucks. I think that's cheaper than new...I can't find my Jegs catalog, and I can't bring it up on jegs.com...probably my crappy spelling.
If this is what you need, I'm more than happy to sell it to you.

09-10-2004, 11:49 AM	#1
greasemonkey Registered User Join Date: Dec 2001 Location: Pace, FL Posts: 2,155	vacuum problem I upgraded to power brakes, and I think I have a problem with my vacuum. I have adjusted the carb (Edelbrock 1406) to get the highest possible reading, about 16.5-17" at the most at idle. Classic Performance says I need at least 18" to work properly. I am pretty sure all the lines are properly sealed. When I hit the brake, the vacuum drops about 3-4" and then regains as I hold the brake. When I release the brake, the vacuum drops about 5" and then rises again. At slow speeds, the brakes work really well, but at speeds above 35 or so, they don't work so well. They apply, but it doesn't stop fast. It will start to slow, then the pedal gets really hard and I can't stop any faster. I used to be able to lock up my old manual drums, but these power discs don't slow very well at all. Sometimes they stick too, and drag just slightly. If I pump the pedal a couple times, they will un-stick themselves. Is all this a sign of poor vacuum, vacuum leak, or something else? I have the original quadrajet intake, and I have heard that I should use the port on it instead of the one on the carb. How do I do this? Thanks, John __________________ 1942 Master Deluxe 1969 C/10 1985 Blazer CUCV 1987 Jimmy 2004 Tahoe 2005 Silverado 1500 2005 Silverado 3500

09-10-2004, 12:09 PM	#2
Gary Senior Member Join Date: Jan 2004 Location: Harvest, AL Posts: 545	I have power brakes too and this sounds almost exactly how my brakes are. The shop I took it too put a big PVC cannister by the brake booster as a vacuum boost I suppose but it still won't "lock" the tires if I hit the brakes hard. I'm having a new intake and carb installed wonder if that will change the available vacuum at all? __________________ Gary Harris 85 Silverado - 87 Grand National 2007 Ardmore Car Show

09-12-2004, 04:51 AM	#4
Gary Senior Member Join Date: Jan 2004 Location: Harvest, AL Posts: 545	So basically these "vacuum canisters" do the same thing that bigass pvc contraption they put on my system does? __________________ Gary Harris 85 Silverado - 87 Grand National 2007 Ardmore Car Show

09-12-2004, 01:06 PM	#5
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Does your brake petal set close to the floor? If so adjust the rod under dash to bring petal up higher. When sdjusted right the petal arm will be in contact with the rubber bumper on bracket. If you run out of adjustment before it reaches bumper you have the wrong adjustment rod--either get one for power brakes or cut into and weld a piece in (this is what I did). This worked for me as I had the same problem(no stopping power). The differance was like going from a 20 oz. hammer to a 10 lb. sledge hammer. Stops with a touch of the toe. It all comes down to leverage. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

09-10-2004, 12:16 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	When I had the first Longhorn, it had power brakes, and when I installed my cammed out 350 in there, vac was in the single digits. I installed a vacume can from jegs and then my brakes worked fine. Well, almost fine. in bumper to bumper traffic, after hitting the brakes and then idling forward, then brake then creep then brake again...that 3rd hit was the last of the vacume assist, and the 4th one with the rock hard pedal would always induce panic. Since an engine naturally makes more vacume in deceleration mode than idle, steady RPM or even revving it up, all you have to do is pop it in neutral and rev it once or twice to 2000 or 2500 RPM.



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