Master Cylinder or Booster
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Freshman User
Joined: Sep 2002
Posts: 47
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From: Friendswood
Master Cylinder or Booster
I'm having problems with my pedel going half way to the floor before the brakes engage and then once they do, you have to keep pressure on the pedal and it eventualy goes to the floor. I've tried bleading all the lines again but no help. I did notice a small seep of fluid where the MC bolts to the Booster. I also have to top off the fluid about once a month. Would replacing the MC fix this or the booster.
Thanks,
Martin
Thanks,
Martin
Postmaster
Joined: Dec 2002
Posts: 3,959
Likes: 9
From: USA
Sounds like you have a leak in the rear seal of the master cyl and it also sounds like the fluid got low enough at one time that it got air in the master cyl and needs to be bled. I would buy a rebuilt master cyl for it and bench bleed it before you put it on. The booster is probably fine.
Senior User
Joined: Jan 2004
Posts: 108
Likes: 0
From: Central Iowa
Check at the wheels too. I had a bad cylinder and every time i pushed the brakes it just drained the fluid and sucked in air. I replaced those and all new hardware too. Cost me only about $25 for cylinders and hardware.
Then a while later the brakes went out again. This time it was the MC. I bought one off a pickup a buddy of mine has out at his place.
Then a while later the brakes went out again. This time it was the MC. I bought one off a pickup a buddy of mine has out at his place.
Senior User
Joined: Sep 2000
Posts: 385
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From: Flat Rock, Michigan
morepower16:
Try this: Start your engine, leave it in park, put your foot on the brake pedal. Hold the pedal down with mild pressure. If the pedal starts to sink down as you apply more pressure, i would suspect that your problem is the vacuum booster. Sometimes you can actually hear the vacuum hissing as you apply pressure to the brake pedal.
But, keep this in mind, if you replace the booster without replacing the master cylinder, you risk the chance of blowing out the (old) master cylinder because the vacuum booster is going to automatically apply more pressure to it than did the leaky booster.
Long story short: replace both items together unless the master cylinder was the problem. Then you can get away with the master cylinder only. Hope this helps.
Also, you said you saw some seepage at the booster where the M/C bolts on. This seepage can get into the booster seals and cause it to leak vacuum. This is usually the cause of booster failure.
good luck.
-hooD
Try this: Start your engine, leave it in park, put your foot on the brake pedal. Hold the pedal down with mild pressure. If the pedal starts to sink down as you apply more pressure, i would suspect that your problem is the vacuum booster. Sometimes you can actually hear the vacuum hissing as you apply pressure to the brake pedal.
But, keep this in mind, if you replace the booster without replacing the master cylinder, you risk the chance of blowing out the (old) master cylinder because the vacuum booster is going to automatically apply more pressure to it than did the leaky booster.
Long story short: replace both items together unless the master cylinder was the problem. Then you can get away with the master cylinder only. Hope this helps.
Also, you said you saw some seepage at the booster where the M/C bolts on. This seepage can get into the booster seals and cause it to leak vacuum. This is usually the cause of booster failure.
good luck.
-hooD
Freshman User
Joined: Jul 2003
Posts: 41
Likes: 0
From: ponoka,ab
hi all. i have a similar problem with a 78 f-250. i was just wondering if the booster is faulty would that cause a vacuum leak? im guessing it would but i thought id ask. inver dealt with the master cy. and a booster before. i will prob have to replace both since isee leakage on the back of the mc. is this a very hard job to bleed the mc? thanx for the help
Senior User
Joined: Sep 2000
Posts: 385
Likes: 0
From: Flat Rock, Michigan
steeldust:
If your booster is bad it will leak engine vacuum, but only when you apply pressure to the brake pedal. If it is leaking vacuum, you will notice a slight decrease in engine rpm's at an idle, but only when you are on the brake pedal.
Bleeding the master cylinder is easily done on the work bench in a vice. Most master cylinders come with directions on the bleeding process that most anyone can follow even if you have never done it before.
Most auto parts stores will sell you the booster and master cylinder combo.
I have replaced the booster and master cylinder 3 times on my 81 F150, but then again i have owned it for 23 years and put on 213,000 miles!
The hardest part of the job is getting the booster off with the 4 nuts that you have to hang upsidedown under the steering column to get off. And sometimes getting the brake pedal dettached from the booster can be a pain too. But it is no worse than changing spark plugs in my opinion. Good luck bro.
-hooD
If your booster is bad it will leak engine vacuum, but only when you apply pressure to the brake pedal. If it is leaking vacuum, you will notice a slight decrease in engine rpm's at an idle, but only when you are on the brake pedal.
Bleeding the master cylinder is easily done on the work bench in a vice. Most master cylinders come with directions on the bleeding process that most anyone can follow even if you have never done it before.
Most auto parts stores will sell you the booster and master cylinder combo.
I have replaced the booster and master cylinder 3 times on my 81 F150, but then again i have owned it for 23 years and put on 213,000 miles!
The hardest part of the job is getting the booster off with the 4 nuts that you have to hang upsidedown under the steering column to get off. And sometimes getting the brake pedal dettached from the booster can be a pain too. But it is no worse than changing spark plugs in my opinion. Good luck bro.
-hooD
Freshman User
Joined: Jul 2003
Posts: 41
Likes: 0
From: ponoka,ab
hi. thanx for the info. the problem i have is when i pump the brakes the idle goes up and my brakes get stronger(harder). i took the the vacuum hose off the booster last night and plugged it to see if there was an effect on idle and it did help but the brakes are scary without the booster.too bad. i can understand the brakes getting better when pumping probably cause of air in the lines but the idle going up? me no understand that. thanx for the help.
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Senior User
Joined: Sep 2000
Posts: 385
Likes: 0
From: Flat Rock, Michigan
steeldust:
Make sure that the vacuum hose going to the booster isn't cracked or loose on the booster nipple when attached. And it seems that you may need to bleed the system too.
-hooD
Make sure that the vacuum hose going to the booster isn't cracked or loose on the booster nipple when attached. And it seems that you may need to bleed the system too.
-hooD
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