The Down Range Forum
Member Section => Down Range Cafe => Topic started by: billt on October 13, 2011, 09:10:00 AM
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Lately, sometimes when I apply the brakes in my truck, there is a "hissing sound" coming from down by the brake pedal. This is a "sometimes" problem that doesn't happen all the time. Sometimes it is only when I depress the pedal, sometimes it continues as long as I hold the pedal down, and sometimes it doesn't occur at all. I should mention that through all of this my brakes work normally with no increase in pedal pressure.......yet.
This all points to the power brake booster. That large round thing the master cylinder mounts to. I don't know how much they run, or how difficult they are to replace. Has anyone done it? If so how difficult of a job is it? I'm told that it can be done without having to bleed the brakes, or entering the system at all. If it's going to be easy I may attempt it. But if it's going to be a PITA I'll just take it in. From what I'm looking at all it seems to involve is removal of the master cylinder from the old booster, then removing the pin attaching the brake pedal, then there are 4 bolts that go through the firewall attaching it. Is there anything I'm forgetting? The problem with these kind of jobs is there can be more to it than it looks like. That is why I'm wondering if any of you guys have done it. I don't want to get in over my head right off the bat.
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I've done it about 35 years ago so I won't try and walk you through it. It's obviously an older truck so a 20 dollar Chiltons Manual from the local auto parts store should have one for the year/make/model of the truck. You may even find a youtube video that shows the steps. It's not difficult but I don't remember if the brakes need bleeding.
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Billt
Not having done this yet but looking at the Chilton manual you don't have to disconnect the brake lines and looks pretty straight forward.
Good Luck
Ranger Dave
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I did a lot of them at the dealership. Pretty easy job if you take your time!
Two bolts to remove master cylinder from the unit;
A large vacuum hose to remove;
Slowly move the master cylinder forward and down away from the booster, and there may be a clip and pin to release from the booster (some just work off contact);
Four bolts to remove booster from the firewall;
A pin and clip attaching the booster rod to the break pedal;
Reverse procedure for installation.
Note:
This is a good time to replace the vacuum check valve on the booster unit.
When you start the truck the first time it will run weird because the booster has no vacuum. It is like having a huge vacuum leak for the first minute.
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I would probably replace the master cylinder as well since the seals and stuff are as old as the truck if it's never been done before.
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Have you tried just bleeding the system ? It would be much less expensive than replacing parts that aren't bad, not to mention your time. (can of Brake fluid ) if it doesn't work then you can go with spending time and money
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I would probably replace the master cylinder as well since the seals and stuff are as old as the truck if it's never been done before.
Good point. But the only time we would replace the master cylinder is if we found break fluid in the booster unit, if the seals were leaking (look for little fountains in the cylinder as the break pedal is depressed), or if we were doing a complete break service (pads, shoes, wheel cylinders), and then we would also flush the lines.
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Have you tried just bleeding the system ? It would be much less expensive than replacing parts that aren't bad, not to mention your time. (can of Brake fluid ) if it doesn't work then you can go with spending time and money
It's BillT....he can afford to sell a couple thousand rounds of .50 cal for parts...or a new truck...
;)
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Have you tried just bleeding the system ? It would be much less expensive than replacing parts that aren't bad, not to mention your time. (can of Brake fluid ) if it doesn't work then you can go with spending time and money
The hissing sound is the sign that the diaphragm has rotted in the folds. When he depresses the break pedal it unrolls the diaphragm folds and the rotten spot is exposed. We used to just replace the diaphragm, but soon no body would supply the part due to liability issues.
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For a Sierra but it's close enough for the basics on your Ford?
She's prettier...
http://www.automd.com/how-to/replace-a-brake-booster-video_7520/
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Have you tried just bleeding the system ? It would be much less expensive than replacing parts that aren't bad, not to mention your time. (can of Brake fluid ) if it doesn't work then you can go with spending time and money
The pedal is good and stout, not mushy. I have no leaks in or around the master cylinder itself. It is only about 6 years old. The hissing tells me it is either the booster or a vacuum hose, or both. None of this looks too expensive regardless if I do it myself, or take it in. The booster on line appears to run around $110.00 to $160.00 depending on model. The labor involved to install it seems to be 1 to 2 hours. A new Vacuum hose around $20.00. So unless it's something else in addition to the booster and hose I'm looking at around $250.00 to $300.00. That isn't as bad as I thought.