No Power Brakes
11-04-2016, 01:58 PM
#1
84SuperCab
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No Power Brakes
All of a sudden I've got no power brakes. Pressing on the brake pedal while driving is just like pressing on the brake pedal with the engine off. I pulled the vacuum hose off the brake booster and have good vacuum there, and no cracks or leaks in the hose. Is there anything else I can check or should I just replace the booster. I replaced it with a booster and master cylinder set about 7 years ago but it hasn't been driven much since then. Seems odd since that's one part that rarely gives any problem.
1984 F150SC 351HO C6, original owner
1984 F150SC 351HO C6, original owner
11-04-2016, 04:49 PM
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84SuperCab
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Google the problem some more and found that the booster check valve also goes bad. Pulled it, and the rubber grommet, that it plugs into out for inspection. The check valve seems to be working but the rubber grommet has 5 or 6 real bad splits in it - could easily be leaking tons of air, and it's running pretty bad as well but I thought I had a carb problem - probably just this vacuum leak. Ill replace that first.
Last edited by BigRed84; 11-04-2016 at 07:03 PM.
11-06-2016, 02:22 PM
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bump....
So is there any other way to verify that the booster is bad ? With the new check valve and grommet, the booster seems to be holding vacuum. With the engine running, I can pull the check valve out of the grommet on the booster and quickly put my thumb over it and feel the vacuum, then after several minutes when I remove my thumb covering the hole, I can feel and hear the booster sucking air in like it still has good vacuum. I'm not losing any brake fluid and there are no signs of brake fluid around the check valve opening or check valve or the vacuum hose, nothing indicating a leaking diaphram. I do have some brakes but have to push extremely hard on the pedal, as if the engine was not running - not good enough to drive around.
So is there any other way to verify that the booster is bad ? With the new check valve and grommet, the booster seems to be holding vacuum. With the engine running, I can pull the check valve out of the grommet on the booster and quickly put my thumb over it and feel the vacuum, then after several minutes when I remove my thumb covering the hole, I can feel and hear the booster sucking air in like it still has good vacuum. I'm not losing any brake fluid and there are no signs of brake fluid around the check valve opening or check valve or the vacuum hose, nothing indicating a leaking diaphram. I do have some brakes but have to push extremely hard on the pedal, as if the engine was not running - not good enough to drive around.
11-07-2016, 10:29 AM
#5
I replaced the booster (and master cylinder at the same time) on my truck. It wasn't too expensive after core return and it wasn't too difficult either. Just a few bolts holding it to the firewall, a couple brake lines to detach, and one pin through the pedal. Just bleed the lines properly after you're done.
11-07-2016, 05:22 PM
#6
I know it's a pain in the @zz but, if the booster has vacuum, pull the brake master cylinder and bench bleed it to insure that it doesn't have an internal leak (if it's leaking internally, there will be no fluid loss).