Vacuum leak? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Robert1970C20rstbukt · 03-14-2005, 12:50 PM

I just now noticed that there's a real loud vacuum leak coming from somewhere near the brake booster in my truck. It's not the hose or the plastic connecter that's attatched to it, I've checked it for leaks and it's good. If the diaphragm in the booster had a hole in it would the leak be able to be heard?

JimKshortstep4x4 · 03-14-2005, 01:14 PM

A leak in the diaphragm can be heard. I would check the master cylinder push rod seal before condemning the booster.

Jim

Robert1970C20rstbukt · 03-14-2005, 03:23 PM

Thanks for the reply Jim. I checked the rubber boot that goes between the master cyl and booster and it is good. The booster I had on the truck was original, and was working great. The master cyl (also original) finally started bypassing fluid and it went bad. Got a new one from O'Reilly's for about $15. Well my Dad thought the booster was bad too so we pulled the old one off and replaced it with one that came off a '72 GMC 1 ton. He didn't even know if it was good or not.

It was working OK for about a week till it started doing this. I just drove the truck again and I think the booster isn't even working, and the leak got louder too. I'll put the old one back on and see what happens.

Robert1970C20rstbukt · 03-14-2005, 11:13 PM

Well, put the old one back on and got the same results. BUT it turns out that IT IS the rubber cup seal between the master cyl and the booster. I tore it when I put it back on.

Can I get one of those at the parts store or do I have to order it from one of the board members?

Thanks for the help

ALSO

Can someone post a pic of a stock vacuum line from the intake to the carb? Right now I have a rubber hose coming straight from the intake to the booster. I have the correct metal line with a fitting and the TH350 detent cable bracket that it goes through but I have no idea how to mount it on the intake.

JimKshortstep4x4 · 03-15-2005, 09:39 AM

I wish that I knew of a source as I need a couple of seals. I posted the question some time back and did not get any responces. Hopefully you can find a source.

Jim

Brainchild · 03-15-2005, 09:52 AM

Taht line should hook to theback of the carb,toward the base if it has a Q-jet on it.

Robert1970C20rstbukt · 03-17-2005, 10:25 PM

Well, found the rubber cup thing that I pulled off the truck that the other booster was originally on, and it worked. Found the right fitting for the carb(Qjet) and hooked everything up and started the engine, I didn't have any problems and the stopping power is awesome now that I put a double diaphragm booster on it.

03-14-2005, 12:50 PM	#1
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Vacuum leak? I just now noticed that there's a real loud vacuum leak coming from somewhere near the brake booster in my truck. It's not the hose or the plastic connecter that's attatched to it, I've checked it for leaks and it's good. If the diaphragm in the booster had a hole in it would the leak be able to be heard? __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

03-14-2005, 03:23 PM	#3
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Thanks for the reply Jim. I checked the rubber boot that goes between the master cyl and booster and it is good. The booster I had on the truck was original, and was working great. The master cyl (also original) finally started bypassing fluid and it went bad. Got a new one from O'Reilly's for about $15. Well my Dad thought the booster was bad too so we pulled the old one off and replaced it with one that came off a '72 GMC 1 ton. He didn't even know if it was good or not. It was working OK for about a week till it started doing this. I just drove the truck again and I think the booster isn't even working, and the leak got louder too. I'll put the old one back on and see what happens. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

03-14-2005, 11:13 PM	#4
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Well, put the old one back on and got the same results. BUT it turns out that IT IS the rubber cup seal between the master cyl and the booster. I tore it when I put it back on. Can I get one of those at the parts store or do I have to order it from one of the board members? Thanks for the help ALSO Can someone post a pic of a stock vacuum line from the intake to the carb? Right now I have a rubber hose coming straight from the intake to the booster. I have the correct metal line with a fitting and the TH350 detent cable bracket that it goes through but I have no idea how to mount it on the intake. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck Last edited by Robert1970C20rstbukt; 03-14-2005 at 11:25 PM.

03-15-2005, 09:52 AM	#6
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	Taht line should hook to theback of the carb,toward the base if it has a Q-jet on it. __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

03-17-2005, 10:25 PM	#7
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Well, found the rubber cup thing that I pulled off the truck that the other booster was originally on, and it worked. Found the right fitting for the carb(Qjet) and hooked everything up and started the engine, I didn't have any problems and the stopping power is awesome now that I put a double diaphragm booster on it. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

03-14-2005, 01:14 PM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	A leak in the diaphragm can be heard. I would check the master cylinder push rod seal before condemning the booster. Jim

03-15-2005, 09:39 AM	#5
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	I wish that I knew of a source as I need a couple of seals. I posted the question some time back and did not get any responces. Hopefully you can find a source. Jim



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