Brake booster - The 1947 - Present Chevrolet & GMC Truck Message Board Network

photoglg · 12-08-2003, 07:38 PM

I am installing power disk brakes on my 69 (front only) and have a few questions: on my intake manifold (250 6 cylinder) there is only one vacuum port and it is being used for the transmission (TH400). Can I use a T fitting for the booster and trans or will I lose enough vacuum to cause problems with both items and if so where can I tap into to get vacuum for the booster? Second Question: I have a manual proportioning value to set bias. People tell that I will need a metering value also, but I have been unable to find any doc that tells me to use a metering value. Anybody out there know about this?

BLACK AND BLUE 67-72 · 12-08-2003, 08:17 PM

Question # 1.You could do the T fitting or does your carb have a port in it that you could use for the booster? Usually a 3/8" plug I think, at the base of the carb.

Question # 2. I have no idea.

photoglg · 12-08-2003, 08:25 PM

B and B the one on the carb is used for my vacuum advance. Thanks, I will try the T

cableguy0 · 12-08-2003, 09:26 PM

that little vaccum part isnt going to pull enough vaccum for the booster and it will not work correctly. you need a 3/8 port thats on its own for the booster otherwise your not going to have any power assist which is very bad with a master cylinder thats made to have power assist

photoglg · 12-08-2003, 09:30 PM

cableguy0 So I may have to tap a second hole in my intake man that will take a 3/8 fitting.

dinnut · 12-08-2003, 09:39 PM

on my 350 4 barrell i already have the hose and everything coming off the bottom of the carb. plate or something?

see the black hose in the front of the pic? thats my vacuum setup for power brakes but i dont have power brakes yet so there is a spark plug -- i didnt do this the po did

photoglg · 12-08-2003, 09:43 PM

Is that your fuel line with the kink in it?

dinnut · 12-08-2003, 10:12 PM

it used to... it still ran amazingly. i replaced it since i took that pic. and yes it was the fuel line

sixty8chev · 12-08-2003, 10:35 PM

Quote:

Originally posted by cableguy0
which is very bad with a master cylinder thats made to have power assist

A bit off topic here, but i just replaced my master cylinder in my 68(non boosted) and my parts guy told me that it was the same as the 71/72 with the booster:

walker · 12-08-2003, 11:14 PM

Just get the prop valve off a power brake truck. You can either drill and tap a hole in your man or I think they sell carb spacers with a hole and hose barb in them. At least they sell them for 4 barrel applications.

woodyjeff · 12-08-2003, 11:15 PM

sixty8chev: the master cylinders for these trucks is the same for with or without power brakes but the master cylinder for the 71/72 is different then the one for the 67-70. The one for 71/72 is shorter and wider and for the 67-70 the cap has to round circles on top of the same size. I think both will work but maybe different mounting holes?

sdredneck · 12-12-2003, 02:48 AM

They make plugs for intakes that are t shaped so that you can run one side for the brake booster and the other for the vaccum modulator for your Tranny

Rooster's 67 · 12-12-2003, 03:15 AM

look at the vaccum port for the pcv it should be 3/8 tee that one to the booster and in that conversion, the later d/b master would be the one to use if the resivor is combined it wont matter, but if it has seperate ones the larger one is for the disks. the calipers requires much more fluid than the small rear cylinders.

Hooter · 12-12-2003, 03:20 AM

i believe there should be a plug on your intak manifold, take the plug out, thread a fitting onto and stick a hose on it

12-08-2003, 07:38 PM	#1
photoglg Registered User Join Date: Jul 2001 Location: Oxnard, CA Posts: 143	Brake booster I am installing power disk brakes on my 69 (front only) and have a few questions: on my intake manifold (250 6 cylinder) there is only one vacuum port and it is being used for the transmission (TH400). Can I use a T fitting for the booster and trans or will I lose enough vacuum to cause problems with both items and if so where can I tap into to get vacuum for the booster? Second Question: I have a manual proportioning value to set bias. People tell that I will need a metering value also, but I have been unable to find any doc that tells me to use a metering value. Anybody out there know about this? __________________ 1969 GMC S/B S/S 3" drop

12-08-2003, 08:17 PM	#2
BLACK AND BLUE 67-72 Firefighter Join Date: Feb 2001 Location: Yellville, Ar, USA Posts: 1,943	Question # 1.You could do the T fitting or does your carb have a port in it that you could use for the booster? Usually a 3/8" plug I think, at the base of the carb. Question # 2. I have no idea. __________________ '72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA

12-08-2003, 08:25 PM	#3
photoglg Registered User Join Date: Jul 2001 Location: Oxnard, CA Posts: 143	B and B the one on the carb is used for my vacuum advance. Thanks, I will try the T __________________ 1969 GMC S/B S/S 3" drop

12-08-2003, 09:26 PM	#4
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	that little vaccum part isnt going to pull enough vaccum for the booster and it will not work correctly. you need a 3/8 port thats on its own for the booster otherwise your not going to have any power assist which is very bad with a master cylinder thats made to have power assist __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

12-08-2003, 09:30 PM	#5
photoglg Registered User Join Date: Jul 2001 Location: Oxnard, CA Posts: 143	cableguy0 So I may have to tap a second hole in my intake man that will take a 3/8 fitting. __________________ 1969 GMC S/B S/S 3" drop

12-08-2003, 09:39 PM	#6
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	on my 350 4 barrell i already have the hose and everything coming off the bottom of the carb. plate or something? see the black hose in the front of the pic? thats my vacuum setup for power brakes but i dont have power brakes yet so there is a spark plug -- i didnt do this the po did Attached Images __________________ 70 longbed 496/th400/Ford 9"

12-08-2003, 09:43 PM	#7
photoglg Registered User Join Date: Jul 2001 Location: Oxnard, CA Posts: 143	Is that your fuel line with the kink in it? __________________ 1969 GMC S/B S/S 3" drop

12-08-2003, 10:12 PM	#8
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	it used to... it still ran amazingly. i replaced it since i took that pic. and yes it was the fuel line __________________ 70 longbed 496/th400/Ford 9"

12-08-2003, 11:14 PM	#10
walker Registered User Join Date: Jul 2003 Location: north of Phx AZ about 30 miles Posts: 698	Just get the prop valve off a power brake truck. You can either drill and tap a hole in your man or I think they sell carb spacers with a hole and hose barb in them. At least they sell them for 4 barrel applications. __________________ Andy,Phx AZ '67 C-10 (Ahhh, done at last. Well there is that disk front end I want to put in and...) "23 C-Cab-sold '48 Ford 8N tractor(still working) '67 Scout(Now on the road) '70 MG B.-sold

12-08-2003, 11:15 PM	#11
woodyjeff Registered User Join Date: Mar 2003 Location: Lincoln, NE Posts: 32	sixty8chev: the master cylinders for these trucks is the same for with or without power brakes but the master cylinder for the 71/72 is different then the one for the 67-70. The one for 71/72 is shorter and wider and for the 67-70 the cap has to round circles on top of the same size. I think both will work but maybe different mounting holes? __________________ 70 Custom-10 LWB

12-12-2003, 02:48 AM	#12
sdredneck The Crazy Kracka Join Date: Dec 2003 Location: San Diego, Ca Posts: 60	They make plugs for intakes that are t shaped so that you can run one side for the brake booster and the other for the vaccum modulator for your Tranny

12-12-2003, 03:15 AM	#13
Rooster's 67 Registered User Join Date: Sep 2003 Location: DFW Posts: 765	look at the vaccum port for the pcv it should be 3/8 tee that one to the booster and in that conversion, the later d/b master would be the one to use if the resivor is combined it wont matter, but if it has seperate ones the larger one is for the disks. the calipers requires much more fluid than the small rear cylinders. __________________ The problem with America is stupidity. I'm not saying there should be a capital punishment for stupidity, but why don't we just take the safety labels off of everything and let the problem solve itself?

12-12-2003, 03:20 AM	#14
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	i believe there should be a plug on your intak manifold, take the plug out, thread a fitting onto and stick a hose on it __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life



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