How long should a brake booster retain vacuum?
#1 _johns_lc_
Posted 22 April 2012 - 05:35 PM
#2
Posted 22 April 2012 - 07:41 PM
How long should a brake booster retain a vacuum after turning the motor off? I'm fitting an electric vacuum pump to an LC with a crazy cam, just so the brakes work. The pump has a cut-in at 15 inches of vacuum and cuts out at 20 inches. Just testing without the motor running, the pump initially builds a vacuum and stops. It fires up again in about a half a minute. This means the vacuum has dropped from 20 to 15 in a half a minute. Is it normal for brake boosters to have such a quick vacuum decay? The check valve seems good. I'm hoping the symptoms suggest a pinhole leak somewhere, diaphragm or something else, because having the pump come on every half a minute is noisy and it'd seem that the pump won't last long with such a high duty cycle.
I don't have any figures on how long a booster should hold vacuum without the engine running but the loss rate you describe seems very unreasonable. I do know that the wife's VS Commodore still has vacuum in the booster even after the engine has been shut down overnight, however, my VZ tonner seems to lose all the vacuum in the booster in the same sort of time frame (has been like that from new).
#3
Posted 22 April 2012 - 07:43 PM
I have set a booster on the vac test unit at my old work and ran the pump to 25" vacuum
Then gone home for the night and checked in the morning... 23"
So if your losing more than 5" in 30 seconds your system is full of leaks
Sadly the electric Vac units really aren't much chop
#4 _johns_lc_
Posted 22 April 2012 - 08:31 PM
#5
Posted 22 April 2012 - 08:37 PM
Very interesting to hear that Mrs. S had vacuum in the morning
Hey John
Hahaha, If Mrs S had vacuum in the morning I would be one very happy camper LOL.
Cheers
Dave
#6
Posted 22 April 2012 - 08:57 PM
The use of a combinded alternator and vaccuum pump as used on some of the modern day diesel engines as an alternative
Have a look for that as it was an interesting read john
#7 _johns_lc_
Posted 22 April 2012 - 09:34 PM
#8
Posted 22 April 2012 - 09:54 PM
But I thought that would be a fairly easy modification to do
Similar to say setting up and running an oil cooler, as this would be on the pressure side of the pump
#9 _Bomber Watson_
Posted 22 April 2012 - 09:59 PM
Cheers.
#10
Posted 22 April 2012 - 10:10 PM
From and expert of the red
Also tagged with one or more of these keywords: brake, booster, vacuum, retention
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