Booster Check Valve question (1 Viewer)

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Mar 7, 2009
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Hey all,

So I took my old booster out today unscrewed the retaining ring and had a look inside - nothing to it really. I did find pieces of my check valve inside the booster :) Aha! moment... maybe this is why my brakes are locking. I do have a question on the actual physics of this thing.

There is a constant vacuum from the manifold to the check valve on the booster.

The check valve stays closed UNTIL the brake is applied which opens the check valve to allow the vacuum to assist in braking ?

My brakes were locking all four discs after just a few miles... Because my check valve wasnt working and the unchecked vacuum was slowly applying brakes ?

Thanks in advance.

JBrakebill
72 FJ40
 
Joined
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check valve

Yes it is actually the ambient pressure that provides the boost -it can do this cause it is working against the vacuum on the other side

When you push the pedal ambient comes in on the side towards the driver and you have vacuum on the other side, when you release the brakes you get vacuum on the side towards the driver equalizing everything again

The check valve is to make sure you have boost enough for a couple applications if the engine dies. It is normally open and shuts to preserve the vacuum on the engine side of the booster


A long time ago I rebuilt one on an old triumph dolomite :)lol::lol:)
I was amazed how simple it was
 
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.... I did find pieces of my check valve inside the booster....... maybe this is why my brakes are locking. ....... Because my check valve wasnt working and the unchecked vacuum was slowly applying brakes ?
JBrakebill
72 FJ40
So....... No. The broken check valve should NOT be the cause of your brakes mysteriously applying.

Yes it is actually the ambient pressure that provides the boost -it can do this cause it is working against the vacuum on the other side

When you push the pedal ambient comes in on the side towards the driver and you have vacuum on the other side, when you release the brakes you get vacuum on the side towards the driver equalizing everything again

The check valve is to make sure you have boost enough for a couple applications if the engine dies. It is normally open and shuts to preserve the vacuum on the engine side of the booster.....
And bsmith explains why here by saying how it all works and giving the true purpose of the check valve.


:cheers:

BTW - I gather from reading a number of threads that "having the length of the rod between the booster and master incorrectly adjusted" is usually the cause of brakes coming on by themselves.
 
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Thanks guys -

I'll leave the vacuum line off and take a drive later today. I'll post tonight.



JBrakebill
72 FJ40
 
Joined
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Messages
8,871
Location
New Zealand
 
 
Thanks guys -

I'll leave the vacuum line off and take a drive later today. I'll post tonight.



JBrakebill
72 FJ40
But that'll leave you without any "brake-boost". So a harder pedal pressure will be needed to stop. ....... So be careful!

(Not advisable to drive in traffic like that!)

But I see what you're doing. If the culprit for the "brake-binding" is the "rod length" between the booster and master - then driving without any vacuum should prevent the brakes from binding (and thus confirm where the problem lies).

Cheers
Tom
 
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in place

you could try pumping the brakes before you move and see if they bind as you pull away a lot of the complaints come after the 2nd or 3rd brake applications

Lost Marbles--good to hear from you again it's been awhile :cool:
 
Joined
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The booster rod length is spot on for the new booster.

After unplugging the vacuum line to the booster the brakes still slowly locked. So, I took off the new booster and put on my old one - with the vacuum line still disconnected and the brakes are no longer locking. Bad valve inside the new booster probably?

JBrakebill
1972 FJ40
 

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