Brake booster - double checking the problem
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Brake booster - double checking the problem
Hi,
On my '77 F150 w/400M when I hit the brake I get a wooshing vacuum-leaking sound from under the dash and the pedal stays awhile, then comes up really slowly. I can also watch the vacuum drop by about an inch at the same time. After searching the archives here I think that means a bad brake booster. Does that sound right?
Disconnecting and plugging the booster vacuum line eliminates the vac leak/drop and the brake acts 'normal' but unassisted (wouldnt want to drive it that way). No fluid is leaking from the booster and the level is good.
Thanks for any input.
Hayward
On my '77 F150 w/400M when I hit the brake I get a wooshing vacuum-leaking sound from under the dash and the pedal stays awhile, then comes up really slowly. I can also watch the vacuum drop by about an inch at the same time. After searching the archives here I think that means a bad brake booster. Does that sound right?
Disconnecting and plugging the booster vacuum line eliminates the vac leak/drop and the brake acts 'normal' but unassisted (wouldnt want to drive it that way). No fluid is leaking from the booster and the level is good.
Thanks for any input.
Hayward
Posting Guru
Joined: Aug 2000
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Brake booster - double checking the problem
Yep, Hayward, it's a bad booster. Make sure the brake rod depth is the same on both the old and new boosters. It has an adjustment that you can screw in or out to get the corect depth.
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Brake booster - double checking the problem
I'd test the check valve before dis-assembling anything.
It's that little plastic thing where the vacuum hose goes on the booster under the hood.
Dennis https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=1733&.jpg
Please Don't Ask Me Any Tough Questions As:
"I'm Saving My Memory For When I Develop Alzheimer's"
78 F-150 429CJ,Silver
w/Explorer Pkge.
641/2-Mustang 260,Pre-World's Fair Car.
64-Fairlane500 S/C waiting for a 390-4spd.
68-Mustang 289-Sunlit Gold 80,892Mi
78-Buick LeSabre 403 4V
84 Volvo DL Wagon
It's that little plastic thing where the vacuum hose goes on the booster under the hood.
Dennis https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=1733&.jpg
Please Don't Ask Me Any Tough Questions As:
"I'm Saving My Memory For When I Develop Alzheimer's"
78 F-150 429CJ,Silver
w/Explorer Pkge.
641/2-Mustang 260,Pre-World's Fair Car.
64-Fairlane500 S/C waiting for a 390-4spd.
68-Mustang 289-Sunlit Gold 80,892Mi
78-Buick LeSabre 403 4V
84 Volvo DL Wagon
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New User
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Brake booster - double checking the problem
What am I checking for? Do I remove it? I didnt notice any cracks or such when I disconnected the vacuum hose.
Sorry, I'm working/learning my way through the truck as things break. The brake system is a new area for me.
Thanks
Sorry, I'm working/learning my way through the truck as things break. The brake system is a new area for me.
Thanks
New User
Joined: Jan 2008
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Brake booster - double checking the problem
E-Mail me directly and I'll send a photo of the 5 step testing procedure.
Dennis https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=1733&.jpg
Please Don't Ask Me Any Tough Questions As:
"I'm Saving My Memory For When I Develop Alzheimer's"
78 F-150 429CJ,Silver
w/Explorer Pkge.
641/2-Mustang 260,Pre-World's Fair Car.
64-Fairlane500 S/C waiting for a 390-4spd.
68-Mustang 289-Sunlit Gold 80,892Mi
78-Buick LeSabre 403 4V
84 Volvo DL Wagon
Dennis https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=1733&.jpg
Please Don't Ask Me Any Tough Questions As:
"I'm Saving My Memory For When I Develop Alzheimer's"
78 F-150 429CJ,Silver
w/Explorer Pkge.
641/2-Mustang 260,Pre-World's Fair Car.
64-Fairlane500 S/C waiting for a 390-4spd.
68-Mustang 289-Sunlit Gold 80,892Mi
78-Buick LeSabre 403 4V
84 Volvo DL Wagon
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
Brake booster - double checking the problem
That whooshing sound means the diaphragm is leaking, it shouldn’t be “sucking” the atmosphere that hard. Time for a new booster. Make sure the pushrod is not adjusted too long, I believe it is just under 1 inch from the tip of the rod to the base of the hole.
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Brake booster - double checking the problem
That was it. Swapping the booster fixed it.
Thanks
Thanks
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Brake booster - double checking the problem
Hayward:
I believe I have the same problem with my '78 F150. I too have suspected my power booster as well. Like you I too am stumbling my way through and learning as I go. Was it difficult? Did you run into anything strange that I should be aware of before I start? Also, did you replace the master cylinder, and if not, what was your method of removing the power booster without messing with the master cylinder?
Havin' Fun and learnin' too!!
Dave
'78 F150
I believe I have the same problem with my '78 F150. I too have suspected my power booster as well. Like you I too am stumbling my way through and learning as I go. Was it difficult? Did you run into anything strange that I should be aware of before I start? Also, did you replace the master cylinder, and if not, what was your method of removing the power booster without messing with the master cylinder?
Havin' Fun and learnin' too!!
Dave
'78 F150
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Brake booster - double checking the problem
It was probably the easiest part I've replaced so far - usually the more important a piece is, the harder it is to replace 
I just unbolted the master cylinder and left it sitting there. You dont have to disconnect the tubes. Then do the vacuum line, the linkage at the brake pedal, and unbolt the booster bracket at the firewall. If you unbolt the booster bracket at the booster, then its a funky trick to get the linkage screw undone while its still attached to the bracket. Screw or unscrew the adjustment nut sticking out of the booster to match your old one (I had no idea what people were talking about until I got there and saw it).
The biggest problem I had was that its failure wore out the front brakes and rotor, and while replacing the roter the locknut simply would *not* budge (was using the correct special tool) so I had to hacksaw off the hub and drive the locknut off with a punch . Talk about a simple procedure gone bad.
So theres my limited experience in a nutshell. Enjoy.
I just unbolted the master cylinder and left it sitting there. You dont have to disconnect the tubes. Then do the vacuum line, the linkage at the brake pedal, and unbolt the booster bracket at the firewall. If you unbolt the booster bracket at the booster, then its a funky trick to get the linkage screw undone while its still attached to the bracket. Screw or unscrew the adjustment nut sticking out of the booster to match your old one (I had no idea what people were talking about until I got there and saw it).
The biggest problem I had was that its failure wore out the front brakes and rotor, and while replacing the roter the locknut simply would *not* budge (was using the correct special tool) so I had to hacksaw off the hub and drive the locknut off with a punch . Talk about a simple procedure gone bad.
So theres my limited experience in a nutshell. Enjoy.
