Vacuum suction spec?
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Senior User
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Vacuum suction spec?
Anybody know what it should be making inHg?
Having power brake issues. Replaced the pump once already, and one year later it's starting again. Basically, pedal hardens up and dash 'brake' light come on at idle/low speed.
Thanks
Having power brake issues. Replaced the pump once already, and one year later it's starting again. Basically, pedal hardens up and dash 'brake' light come on at idle/low speed.
Thanks
Hotshot
Joined: Mar 2014
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From: Douglassville, PA
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Senior User
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OK.
In inHg:
Vacuum on hose out of pump is 5 idle, 15 at 2100 rpm.
Vacuum on the distribution manifold is 2.5 idle, 11.5 at 2100 rpm.
And it's a gradual drop back, about 3 sec, to idle vacuum when I take foot of accelerator.
In inHg:
Vacuum on hose out of pump is 5 idle, 15 at 2100 rpm.
Vacuum on the distribution manifold is 2.5 idle, 11.5 at 2100 rpm.
And it's a gradual drop back, about 3 sec, to idle vacuum when I take foot of accelerator.
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Senior User
Joined: Jun 2015
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Never did find specs for mechanical vacuum pump, but based on generic numbers my pump was way low.
Changed it out, along with power booster check valve.
New pump running 25 inHG at idle. Brakes all good.
Changed it out, along with power booster check valve.
New pump running 25 inHG at idle. Brakes all good.
Elder User
Joined: Sep 2011
Posts: 979
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From: Vancouver
Another way to approximate what the vacuum should be is that a gas engine max vacuum is in the low 20 inches, so those vacuum systems are designed for use on gas engines. The pumps are just imitating to make the same equipment like hvac controls and brakes operate the same way. For motor homes with vacuum systems, they just use more vacuum diaphragms for the rear brakes.
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