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Old 09-10-2019, 08:20 AM   #1
bonnie&clyde
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Default Brake vacuum pump

Im about to pull all my hair out on this one. I wasn't too happy with my braking power in my 92 so i decided to put a LEED Bandit vacuum pump to help. Issue is the pump is suppose to shut off at 25inches of vacuum, but when i hook it up directly to the brake booster it never passes 18inches of vacuum so the pump is always on, this is the second brake booster in the last month since the first one had a leak. Do i have another bad brake booster? Or do they just not get over 18inches of vacuum?? To test it i pulled the hose from the booster and put my finger at the end of the hose and the gauge goes up to 25 and the pump shuts off, as soon as i hook it up to the booster still only 18.
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Old 09-10-2019, 09:39 AM   #2
Stangs 4 Life
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Yes, it's bad. Hopefully under warranty.
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Old 09-10-2019, 10:53 AM   #3
shumpertdavid
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I sounds like a bad booster again.
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Old 09-10-2019, 10:58 AM   #4
bonnie&clyde
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Shit... so a new brake booster should reach 25inches of vacuum?
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Last edited by bonnie&clyde; 09-10-2019 at 12:10 PM.
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Old 09-14-2019, 08:26 AM   #5
garycrist
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Sometimes IIRC if the booster rod length was too long, it
would "actuate" the booster and allow the booster to
leak into the passenger compartment.
(Disconnect the booster pedal rod from the pedal
and gently pull the rod. If vacuum come up you know the drill.
If not well find a new Cobra unit).

It seems like we always had problems with rebuilt units too.
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Old 09-14-2019, 12:21 PM   #6
shumpertdavid
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Engine vacuum is usually in the 18-20" range (stock motor, good valve seal to the head, etc), on heavy decel it will go higher. I'd say it's safe to assume a vacuum booster should withstand 25 inches. I've never had to verify that in my years of auto repair but it's definitely feasible from using a vacuum gauge looking at various other issues.

20"s would be a more common number for a booster to see and in my opinion the pump would be better suited set @ there.
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