vacuum source & line - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering
User Name
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 12-01-2007, 03:27 PM
Registered User
Last photo:
Join Date: May 2007
Location: Bastrop, Tx
Posts: 212
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
vacuum source & line

I have a '56 F100 powered by 283 Chevy, mild cam with a CPP Power Brake kit w/ Prop. valve. Disc up front on my MII and Drum on my 9". I think my brakes lack the power assist that they should have therefore; I have 2 Ques :
1) Which is a better source for the vacuum, the back of my Carb or the Intake?
2) Of what material should the vacuum line be.....presently just have a 3/8" gas line hose. (It's about 4 foot long due to the Booster/Master located under cab.)

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 12-01-2007, 10:17 PM
Registered User
Join Date: Nov 2007
Location: brisbane australia
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
heya bud, not an expert BUT , the vac take off should be the same when hooked from the carby base or direct to intake pressure , get a vac gauge and check - it should be up around 18-plus except for when you open the throttle, see what she measures up to and then u can start figuring why its low or whatever...could be the booster is sluggish or whoknows , start with the vac gauge , keep in touch with ya news cya Rix66
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-01-2007, 10:49 PM
powerrodsmike's Avatar Moderator
Last wiki edit: Make a fiberglass fan shroud
Last journal entry: Next.. ..Bagging the king B (barge)
Last photo:
Join Date: Jan 2005
Location: gilroy, california
Age: 56
Posts: 4,104
Wiki Edits: 161

Thanks: 0
Thanked 3 Times in 3 Posts
Rix66 is right about the carb base or manifold, either port should deliver enough vacuum, anything above 16" you should see some assist especially at speed. Don't forget, usually you are creating more vacuum at speed when you take your foot off the gas, throttle plates close, vacuum goes up.

Check your hose, it may be collapsing. I use either 3/8" vacuum hose, (thick wall stuff, won't collapse), or 3/8 steel tube, with short lengths of hose to connect at the ends.

What size booster are you using? A 7" single diaphram booster will only give minimal assist, especially at lower vacuum levels..

You can check the booster by shutting the motor, pump the brake pedal a few times to allow the booster to drain it's vacuum,(how can you drain something that isn't there?hhahaha).

Then put your foot on the brake pedal and apply some constant pressure, just till you feel resistance. Then start the motor...if you feel the pedal get easier to push, and "fall" under your foots pressure as the motor pulls a vacuum on the booster,, then the booster is probably working.

You could have too big a master cylinder, wrong pedal ratio or you might just have glazed pads or too small a rotors, etc,etc. There are many other things that could cause poor brakes.

HTH, mikey
my signature lines...not really directed at anyone in particular..

BE different....ACT normal.

No one is completely useless..They can always be used as a bad example
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-02-2007, 07:18 AM
F&J F&J is offline
Registered User

Last journal entry: 32 Ford cabriolet conversion/windshield
Last photo:
Join Date: Mar 2007
Location: Connecticut
Age: 65
Posts: 1,571
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Also make sure that there is the one-way vacuum check valve where the fitting is on the vacuum booster. If it is there, it should hold vacuum in the booster after the motor is shut off.

I'd take the truck on a short run in normal driving; then stop and feel all 4 brakes for normal temps, and be looking for "cold" brakes on one axle. Sometimes you can have a bleeding problem or valve problem and you are only stopping on one pair of brakes.....been there, done that
Reply With Quote Quick reply to this message

Recent Suspension - Brakes - Steering posts with photos

Quick Reply

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
detonation 71 chevy c-10 Engine 33 04-29-2010 12:20 PM
Vacuum line pics/diagram for 305 w/ Qjet? hon_jr Engine 15 08-31-2007 08:25 AM
vacuum line, what size ? fat50chevy Transmission - Rearend 4 06-14-2006 09:43 PM
help with vacuum line to heater in '72 camaro bullheimer Interior 7 01-10-2005 06:00 PM
early optispark vacuum source 48Man Engine 7 01-16-2003 01:17 PM

All times are GMT -6. The time now is 08:24 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.