Lack of Vacuum - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Bud69CheySB · 08-22-2002, 08:17 PM

Looking for a solution on lack of vacuum. I have a 69 Chevy with a 96 Lt1 Engine that has been modified and only produces around 9/10 inchs of vacuum. I was informed I need 16 inchs for my power brakes. Looking for a electric vacuum pump or ideas that would work. It's a blast to drive with out much brakes.
Thanks

Hooter · 08-22-2002, 08:42 PM

do u have a radical cam in it or something?. If so you should invest in a vacum pump i have seen them in the summit catalogue.
If its stock you are going to have to find the vacum leak. It could most likely be on the throttle body or on any of the other lines.

lofly'a · 08-22-2002, 08:55 PM

you can get a vac. accumulator canister that stores "vacuum surge", not sure if you have enough vacuum for that though. summit and jegs carries the vac. pump. another trick but sometimes inadequate alternative is to swap in a hydraulic booster from a diesel pickup or some 3/4 and 1 ton units. these tie into the power steering pump. i've driven a few that work real good and some that really suck, as in when you're turning the wheel and braking at the same time theres just not enough pressure to supply both accessories

Michael A. K. G · 08-23-2002, 11:04 AM

A *steady* 9 or 10 inches at idle indicates a vacuum leak. You should have no trouble getting up to 16 inches.

Make sure all the vacuum lines are connected and routed correctly, and that none of them are cracked or loose. Then idle the engine and spray carburator cleaner around all the intake gaskets between the throttle body and the head. Any change in idle means you found a vacuum leak. Also, if you have power brakes, try squeezing the tar out of its vacuum line with pliers, with the engine idling. Any change in idle indicates a leaky power brake booster. If you STILL don't find the problem, try disconnecting each line in turn at the intake side and plug the port, and remeasure the vacuum.

Finally, if your vacuum has regular low jumps, you may need a valve job, or your ignition system may be "missing."

69sixpackbee · 08-23-2002, 11:38 AM

I have used a vacuum pump from a Caddy diesel on my race/street cars. They are wired into the brake light switch system just like the original cars had them. You can pick these up at a junk yard for a few bucks. It helps plumbing the vac into a reservoir as well to give you extra volume.
Still even a fairly decent camshaft on the street should yield at least 13 in/hg. Check for leaks. (get out the WD-40!)

08-22-2002, 08:17 PM	#1
Bud69CheySB Registered User Join Date: Apr 2000 Location: Wylie, TX USA Posts: 24	Lack of Vacuum Looking for a solution on lack of vacuum. I have a 69 Chevy with a 96 Lt1 Engine that has been modified and only produces around 9/10 inchs of vacuum. I was informed I need 16 inchs for my power brakes. Looking for a electric vacuum pump or ideas that would work. It's a blast to drive with out much brakes. Thanks __________________ Bud

08-22-2002, 08:42 PM	#2
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	do u have a radical cam in it or something?. If so you should invest in a vacum pump i have seen them in the summit catalogue. If its stock you are going to have to find the vacum leak. It could most likely be on the throttle body or on any of the other lines. __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

08-22-2002, 08:55 PM	#3
lofly'a Registered User Join Date: May 2000 Location: Alexandria, LA 71301 Posts: 1,451	you can get a vac. accumulator canister that stores "vacuum surge", not sure if you have enough vacuum for that though. summit and jegs carries the vac. pump. another trick but sometimes inadequate alternative is to swap in a hydraulic booster from a diesel pickup or some 3/4 and 1 ton units. these tie into the power steering pump. i've driven a few that work real good and some that really suck, as in when you're turning the wheel and braking at the same time theres just not enough pressure to supply both accessories __________________ -02 avalanche (daily driver) -66 gto ragtop 389/400 (garage queen, hand-me-down from dad) -72 Tribute Trans Am (6.0LS/T56 6-speed) in progress -2003 YUKON (Wife's) -71 gmc swb fleet (current project, gonna shave everything, bags, stuff w/ 20's, gen III powertrain) -48 3100 SWB - 12/31/23 LONG TERM Project

08-23-2002, 11:04 AM	#4
Michael A. K. G Registered User Join Date: Jul 2002 Location: California central coast Posts: 126	A steady 9 or 10 inches at idle indicates a vacuum leak. You should have no trouble getting up to 16 inches. Make sure all the vacuum lines are connected and routed correctly, and that none of them are cracked or loose. Then idle the engine and spray carburator cleaner around all the intake gaskets between the throttle body and the head. Any change in idle means you found a vacuum leak. Also, if you have power brakes, try squeezing the tar out of its vacuum line with pliers, with the engine idling. Any change in idle indicates a leaky power brake booster. If you STILL don't find the problem, try disconnecting each line in turn at the intake side and plug the port, and remeasure the vacuum. Finally, if your vacuum has regular low jumps, you may need a valve job, or your ignition system may be "missing."

08-23-2002, 11:38 AM	#5
69sixpackbee Registered User Join Date: Jan 2001 Location: Sabinal, Texas Posts: 1,706	I have used a vacuum pump from a Caddy diesel on my race/street cars. They are wired into the brake light switch system just like the original cars had them. You can pick these up at a junk yard for a few bucks. It helps plumbing the vac into a reservoir as well to give you extra volume. Still even a fairly decent camshaft on the street should yield at least 13 in/hg. Check for leaks. (get out the WD-40!)



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