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Discussion Starter · #1 ·
87 XLT, 302
I just got this truck, knowing it would need a brake job soon. It happened a little sooner than I expected. Last time I cranked up, the brakes became nearly unresponsive and required me to press as hard as I could to slowly come to a stop. When I press the brakes now I hear a sound like a pressurized gas leak (like a hole in a tire, etc.). This is driveable but NOT safe.

I really dont know much...Ive been told that this could mean that the master cylinder needs to be replaced. I really just want a dignosis here so I can find out what to search the threads for (Im sure someone else has had this problem explained).

Thanks for any help!
Jake
 

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Brake booster. Consider yourself lucky if its just the hose.
What he said.....

A brake booster uses engine vacuum to help apply the brakes. With the booster inop or unhooked the brakes become VERY hard to depress. The hissing sound is the vacuum leak. Check the line running from the booster to the engine for holes...if you don't find any then replace the booster.

Derek
 

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Discussion Starter · #6 ·
Yesterday I disconnected the vacuum hose from the booster and found no leaks in it...

When I hit the brakes with everything connected the engine dips (just as it would with the vacuum hose disconnected from the booster and not sealed)...this makes me think that the brake booster is no longer sealed and airtight.

Is it possible with these symtoms that the problem is not the brake booster? (could it still be the mc?)


Im going to check out Steve83's stuff. Thanks.
 

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the mastercylinder could be leaking brake fluid, witch caused the booster to go out.. best thing to do would buy a booster with the mastercylinder. But no these symtoms could not be just the mastercylinder, it has to be the booster, or both..
 

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Discussion Starter · #9 ·
After more research, I really think that it is the booster and not the mc.

but before I buy a new one....
Could it be a fixable leak?

The seal around the peice that connects the vacuum hose to the booster looks bad... could this be it?
Could this be fixable without replacing the entire booster?

I also wonder...why can I hear the vacuum so much better in the cab than under the hood?
(I do have poor hearing and a very dirty K&N...so it may be just as loud under the hood...I cleaned my K & N last night so maybe it will be more quiet so I can hear the leak.)
 

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I just did the booster replacement. Not hard if the four nuts on the booster weren't rusted to the bolts. Just be ready for the small issues, I ended up replacing that , the mc, and when I went to bleed the brakes, the right front caliper and brake pads. And I still haven't figured out how to adjust the push rod on the booster to where it should be.( brakes give a clunk once in awhile.) Also the rod from the power booster that connects to the brake pedal is wider and is a real pain getting your brake light switch re-hooked up. Good luck!!
 

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Discussion Starter · #11 ·
Alright guys, Im gonna get started on the booster replacement.
Thanks for all the help.

Steve83, I did check your site, it was VERY helpful and helped me understand how the booster works....I just didnt realize what exactly would fail when it broke...so didnt know why the sound would be loud in the cab.
 
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