Converted to Power Brakes not enough vacuum? - Vintage Mustang Forums
 1Likes
Reply
 
Thread Tools
post #1 of 27 (permalink) Old 06-09-2019, 11:10 AM Thread Starter
Member
 
Join Date: Sep 2018
Location: NW Florida
Posts: 34
Garage
Converted to Power Brakes not enough vacuum?

Anybody converted to power brakes only to find your cam isn't allowing enough vacuum for the brakes to work?
My '70 was originally non-power drum brakes all around. I installed one of the full kits from Master Power Brakes, upgraded to power brakes with disc up front. Now, I get a hard pedal before a full pedal push, pretty sure my problem is that I'm only pulling about 13 in vacuum. Hate to spend $100's on an electric vacuum pump.
boss driver is online now  
Sponsored Links
Advertisement
 
post #2 of 27 (permalink) Old 06-09-2019, 11:16 AM
Senior Member
 
MrFlash's Avatar
 
Join Date: Apr 2018
Location: JAX
Posts: 595
What are your cam specs?
What you describe is common.
But first check for vacuum leaks.

And make sure the hydraulics are fully bled.

1970 Mustang coupe

Last edited by MrFlash; 06-09-2019 at 11:18 AM.
MrFlash is offline  
post #3 of 27 (permalink) Old 06-09-2019, 11:56 AM Thread Starter
Member
 
Join Date: Sep 2018
Location: NW Florida
Posts: 34
Garage
Unfortunately I don't have the cam specs, I built the motor 15 years ago but went overseas immediately afterwards. The motor...and the brakes for that matter, have 3 miles on them. I just got back to the states and finished up the car. I did notice the inlet valve to the master cylinder could be a small problem. I understand that should be a one-way valve? But I can move air in both directions through it. Nothing else appears to be a vacuum issue.
boss driver is online now  
 
post #4 of 27 (permalink) Old 06-09-2019, 12:02 PM
Senior Member
 
awhtx's Avatar
 
Join Date: Sep 2011
Location: The Hill Country of Central Texas
Posts: 8,754
Have you considered hydroboost brakes?
awhtx is offline  
post #5 of 27 (permalink) Old 06-09-2019, 12:31 PM
Senior Member
 
MrFlash's Avatar
 
Join Date: Apr 2018
Location: JAX
Posts: 595
Yes. There should be a check valve in the vacuum line between manifold and booster.

Hydroboost will work. But the install is messy and not cheap.

A vacuum reservoir may help get a full pedal pump or two.

1970 Mustang coupe
MrFlash is offline  
post #6 of 27 (permalink) Old 06-09-2019, 12:35 PM
Senior Member
Supporting Member
 
Groundpounder17's Avatar
 
Join Date: Jul 2014
Location: Louisville, KY
Posts: 478
What about spending $75 for a vacuum reservoir

67 Fastback S Code, Brittany Blue

Work in progress
Groundpounder17 is offline  
post #7 of 27 (permalink) Old 06-09-2019, 12:40 PM Thread Starter
Member
 
Join Date: Sep 2018
Location: NW Florida
Posts: 34
Garage
A check valve, in addition to the elbow at the booster?
boss driver is online now  
post #8 of 27 (permalink) Old 06-09-2019, 12:41 PM Thread Starter
Member
 
Join Date: Sep 2018
Location: NW Florida
Posts: 34
Garage
I have, but if my current vacuum number isn't high enough for proper operation, I'm not sure that storing additional volume at that level would matter.
boss driver is online now  
post #9 of 27 (permalink) Old 06-09-2019, 01:06 PM
Senior Member
 
196667Bob's Avatar
 
Join Date: Jul 2013
Posts: 379
Might be an obvious question, but do you have the correct intake manifold fitting that has a threaded port for a 3/8" steel tube flare fitting, which then connects to the 3/8" ID Vacuum Hose ? Using a fitting with a smaller port will not allow the full vacuum to be supplied to the booster ; especially if other options/ accessories are also connected to it. The booster requires the full vacuum.

Just a thought.

Bob
196667Bob is offline  
post #10 of 27 (permalink) Old 06-09-2019, 01:59 PM Thread Starter
Member
 
Join Date: Sep 2018
Location: NW Florida
Posts: 34
Garage
Quote:
Originally Posted by 196667Bob View Post
Might be an obvious question, but do you have the correct intake manifold fitting that has a threaded port for a 3/8" steel tube flare fitting, which then connects to the 3/8" ID Vacuum Hose ? Using a fitting with a smaller port will not allow the full vacuum to be supplied to the booster ; especially if other options/ accessories are also connected to it. The booster requires the full vacuum.

Just a thought.

Bob
Running an Edelbrock intake but using the stock vacuum port...but, I'll double check and make sure I'm not impeding flow, thanks!
boss driver is online now  
post #11 of 27 (permalink) Old 06-09-2019, 02:05 PM
Senior Member
 
Join Date: Sep 2014
Location: Santa Clarita,CA
Posts: 1,108
All the band-aids in the world will not operate your booster safely drawing only 13 in-Hg of vacuum. I believe a quick call to any brake supplier will confirm it. I was advised of this when I purchased my Master Power Brakes kit years ago.


'66 GT Fastback, 302, Edelbrock Top End, Sniper EFI/Aeromotive, MSD, JBA Headers & 2.5" Exhaust, T5Z, Currie 3.55 Trac-Loc
rhutt is online now  
post #12 of 27 (permalink) Old 06-09-2019, 02:12 PM Thread Starter
Member
 
Join Date: Sep 2018
Location: NW Florida
Posts: 34
Garage
Quote:
Originally Posted by rhutt View Post
All the band-aids in the world will not operate your booster safely drawing only 13 in-Hg of vacuum. I believe a quick call to any brake supplier will confirm it. I was advised of this when I purchased my Master Power Brakes kit years ago.
Did you have a vacuum issue? If so, what is/was your fix?
boss driver is online now  
post #13 of 27 (permalink) Old 06-09-2019, 02:27 PM
Senior Member
 
Join Date: Oct 2009
Location: far east north corner of Texas
Posts: 6,494
Garage
My engine idles at 9 or 10 inches of vacuum but when the engine rev's into its mid range the vacuum goes on up to around 15 and then starts dropping back down again as I get on up to wide open. I have manual disc brakes so I'm just contemplating the situation.



I think all you need is a vacuum canister with a check valve to keep the vacuum from bleeding back off. These are generally decent sized and one should store enough vacuum to run the brakes. This obviously won't work if you are doing continual repeated braking like on the Nurburgring but otherwise it should be ok. I would try that first anyway at least. When you cold start and before you take off somewhere you may need to rev the engine for a bit to get the vacuum canister back to where it needs to be to supply the booster.



Before you decide to do this it would probably be best to see just what your vacuum is at what rpm.


65 2+2, 331, C4 presently apart for complete a restore
1979 Ford F150 custom, 302, C4, AC, tilt wheel, main transportation
macstang is offline  
post #14 of 27 (permalink) Old 06-09-2019, 02:29 PM
Senior Member
 
Join Date: Jul 2000
Location: SF Bay Area
Posts: 8,353
Garage
For a factory Midland Booster, 13" vacuum at idle is enough to run power brakes. If your booster is not factory, you will need to confirm with the manufacturer what is the minimum needed.

url]http://i87.photobucket.com/albums/k156/jefftepper/IMG_0027_edited-1.jpg[/url]

*Principal wrench on this 69 Mach I*
JeffTepper is offline  
post #15 of 27 (permalink) Old 06-09-2019, 03:16 PM
Senior Member
 
my289's Avatar
 
Join Date: Sep 2016
Location: Tx
Posts: 617
I ran into this situation and I used a vacuum reservoir and made the brakes feel a lot better. Not a complete solution but the easiest and cheapest. I also have 13" of vacuum with my cam and I know mine needs at least 15" to function properly.
rpm likes this.

1967 Mustang Convertible, 289-4v, C4, Edelbrock Performer Intake, Mild Cam.
my289 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Vintage Mustang Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in













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 On
Trackbacks are On
Pingbacks are On
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome