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#1 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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vacuum leak? maybe break booster?
Hello All!
First off I'd like to say this form has helped me out tremendously over the years. The knowledge and know how is next to none. I have a 72 c20 rebuilt 350, old th300. I've been trying to track down what I believe to be a vacuum leak. After doing some searching, I found out about break boosters causing vacuum leaks due to a torn diaphragm. The truck idles prefect accept for when I'm stopped at a light for a few minutes. It then start to surge. As soon as I accelerate, the surge goes away. Only when I stop at a light again, it starts back up. It only happens when I have the breaks on for over a few mins. On short stops, there is no problem. Today I took the vacuum hose going to the booster off while it was surging. I had it on my street with the ebrake on, chucks under the tires, and in drive. Once I plugged the hose the idle went up and the surge went away. Does this sound like I need to replace my break booster due to a torn diaphragm? Thanks, Kelz Posted via Mobile Device |
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#2 |
Registered User
![]() Join Date: Jul 2007
Location: New River Arizona
Posts: 1,180
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Re: vacuum leak? maybe break booster?
It sounds like it may be a possibility. There are usually some signs leading to the problem. Are the brakes getting harder to push? Do you hear any vacuum hissing noise. Is the one way valve at the booster attached to the hose good? It is a 1 way valve and should only work in 1 direction. Have you taken the master cylinder loose to see if it has leaked fluid into the booster? This will wreck the diaphragm. I would check for these things before changing it out.
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#3 | |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Quote:
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#4 |
Registered User
Join Date: Mar 2012
Location: Boulder, CO
Posts: 350
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Re: vacuum leak? maybe break booster?
I vote for bad booster- the increased pedal pressure is a tip-off. Checking for a leak into the booster from the master cylinder will be easy, once the booster is removed. Be prepared to replace the master cylinder, too. PITA, but, it'll be cheaper than using some one else's car to stop with.
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#5 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,638
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Re: vacuum leak? maybe break booster?
Seperate the brake vacuum hose from the pcv. They aren't supposed to be teed togethor.
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#6 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,943
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Re: vacuum leak? maybe break booster?
Yup... need a dedicated vacuum line to each one.
Gary
__________________
'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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#7 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
I'm planing on buying a master cylinder with the break booster if it's bad. Sometimes working on these truck is a PITA but it's definitely worth it.
I only have one available manifold vacuum port on my carb. It's a quick fuel 650. Should I tie the PCV valve into the back of the carb and tied the break booster to the edelbrock intake? I see there's a place to screw in a brass fitting on the back of it. |
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#8 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,638
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Re: vacuum leak? maybe break booster?
Yes!
Plug pcv into carb. Use a vacuum tree on the intake. Like these. https://www.paragoncorvette.com/c-22...aspx?pagenum=1 |
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#9 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
I'll pick one up Sunday and fix thoes vacuum lines. Just to make sure. I have the automatic transmission vacuum hose going to the manifold vacuum on the front of the carb. I have the advanced timing going to the advanced port and the pcv will go to manifold vacuum on the back of the carb. The only hose I'm running to the intake is the break booster. Should I get a tree with the 3/8 port for the booster and cap off the smaller port incase I need an extra manifold vac in the future?
Also, could the pcv and the booster being teed cause the surge I'm having at stoplights? |
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#10 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
I know everyone likes to see pics. Here's a couple of the truck
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#11 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
Couple of the motor
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#12 | |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,638
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Re: vacuum leak? maybe break booster?
Quote:
Hook the pcv to your carb. Hook the booster and your tranny to a vac tree on the manifold. The tranny needs full time vac. You might not have much room for a vac tree behind your carb. Not a problem. The fix costs money but has two benefits. You need a carb spacer/heat insulator under your carb anyway so raising the carb an inch will give you room for a tee. Your carb might be boiling a bit which also makes it surge. Looks like you're gonna burn a couple plug wires on your header. You have enough length in the wires to run them underneath. Also what fuel pressure are you running with your regulator? |
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#13 |
Registered User
![]() Join Date: Feb 2013
Location: Spring Hill, Florida
Posts: 465
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Re: vacuum leak? maybe break booster?
yep the factory hooked the pcv to the carb and the booster and trans to the manifold. I also second adding a 1" spacer under the carb. not 1/2" not 2" a 1" spacer. being a Holley you probably can pick one up at the parts store.
here are a couple of quick shots of how mine is hooked up, should be about the same for you. BTW nice setup. |
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#14 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
Thanks for the info guys! I'm gonna go to the AP store tomorrow. Hopefully they carry the vac tree I need. If they dont, I'll have to wait until Monday and head over to the speed shop. I know it doesn't look like it in the first pics, but I have a 1" spacer already. It's a must out here in the desert. I learned a couple years back when I had the edelbrock on the motor and fuel was boiling in the bowl.
Geezer#99, I never thought about running the wires under the headers. If they're long enough, I'll do that tomorrow. I have the fuel pressure regulator set at 6.5psi. At least I hope that's where it's set. The gauge is all over the place. I think the heat messes with it because it's never consistent. Mr Handy, your setup look really good too. I hope to have mine running like a champ soon. I'll get back on tomorrow and let you guys know how everything goes. |
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#15 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
So after a week of rainy days off and work I had a chance to go grab a 3/8nmpt to 3/8 hose. Had to grab it from All Hose here in Vegas because none of the AP stores sold one that had a 90° angle. I tightened it to the intake and ran the break booster to it. Got rid of the "T" and ran the pcv to the carb. It seems to be running alot better now. I took the truck on a long test drive and it seems like the surging has stopped. I guess I'll see in the next couple of days if I still have a problem.
Thanks everyone for the help!!! Posted via Mobile Device |
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#16 |
Registered User
Join Date: May 2014
Location: Mobile, AL
Posts: 422
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Re: vacuum leak? maybe break booster?
Hope you got it worked out! You can put a vacuum pump on your booster, pump it up to 20 and wait a few minutes to see if it can hold the presure.
Also gotta ask, is that an orange truck with a black hood? .....lol |
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#17 | |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Quote:
Nope, close. It's an orangish, rustish, primerish truck with a gray hood. Close though haha! Is that your truck? It looks sweet Posted via Mobile Device |
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#18 |
Registered User
Join Date: May 2014
Location: Mobile, AL
Posts: 422
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Re: vacuum leak? maybe break booster?
Haha, yea that's my beater. Camera makes it look 20 years younger though lol!
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#19 |
Registered User
Join Date: May 2014
Location: Mobile, AL
Posts: 422
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Re: vacuum leak? maybe break booster?
Hers a pic of mine. It was like 20 bucks, just in case you weren't familiar with them.
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#20 |
Registered User
Join Date: Jun 2013
Location: las vegas nevada
Posts: 60
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Re: vacuum leak? maybe break booster?
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