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.
How long should a brake booster retain vacuum?
Started by
_johns_lc_
, Apr 22 2012 05:35 PM
brake booster vacuum retention
9 replies to this topic
#2
S pack
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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
dattoman
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Posted 22 April 2012 - 07:43 PM
You will find this whole setup dissapointing
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
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_
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Posted 22 April 2012 - 08:31 PM
S pack and dattoman, thanks very much for the replies. I've had a look around at searches and forums and so on and not found any thought on the question I asked. Very interesting to hear that Mrs. S had vacuum in the morning, just the sort of thing I wanted to hear. Similarly 23/25 for dattoman in the morning. Indeed I have leaks in the booster then. These might be fixed and the pump won't be noisy so often! But datto, you have no faith in electric pumps?
#5
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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
AbsynthHatch
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Posted 22 April 2012 - 08:57 PM
Datto pointed out in another thread
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
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_
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Posted 22 April 2012 - 09:34 PM
AbsynthHatch, thanks, I looked at the idea of diesel alternators for the torana red motor, but doesn't it take oil connections for that? Haven't caught up with what datto said in the other thread.
#8
AbsynthHatch
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Posted 22 April 2012 - 09:54 PM
Yes you are correct, it does take oil connections
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
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_
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Posted 22 April 2012 - 09:59 PM
T piece off the oil pressure port, return to sump, fuel pump area, timing case, wherever convenient.
Cheers.
Cheers.
#10
AbsynthHatch
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Posted 22 April 2012 - 10:10 PM
There you go John
From and expert of the red
From and expert of the red
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