Brake light switch/ "proportioning valve"
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 2,812
Likes: 4
From: Gig Harbor Wa
Brake light switch/ "proportioning valve"
I know that at least on the early C3's the proportioning valve is not really a valve, but a differential switch to light up the dash light if you loose pressure one side.
Now for my question. If you loose pressure on one side, lets say rear, will the piston shift over and stop all fluid flow, or will it just move over and still allow fluid to pass to the rear circuit.
The reason I am asking is I am installing dual master cylinders of different sizes on my car and would like to keep the light switch. I guess its really not that important, but would make the plumbing a little easier.
Thanks
Now for my question. If you loose pressure on one side, lets say rear, will the piston shift over and stop all fluid flow, or will it just move over and still allow fluid to pass to the rear circuit.
The reason I am asking is I am installing dual master cylinders of different sizes on my car and would like to keep the light switch. I guess its really not that important, but would make the plumbing a little easier.
Thanks
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
As I remember from real life 
, it allows the remaining two brakes to function correctly. You can limp home if this happens (or in my case, drive for approximately 6 months while saving for new calipers.) Black electricians tape shields the driver from the glare of the red brake light... 
(I'll verify this with my assembly manual and get back...)
, it allows the remaining two brakes to function correctly. You can limp home if this happens (or in my case, drive for approximately 6 months while saving for new calipers.) Black electricians tape shields the driver from the glare of the red brake light... (I'll verify this with my assembly manual and get back...)
Drifting
Joined: Jan 2006
Posts: 1,832
Likes: 38
From: Cedar,BC
It is actually a combination valve.It makes the brake warning light operate in case of a hydraulic failure on one side of the system and limits the pressure to the rear brakes during normal operation.If you are putting in dual masters you probably will want to put in an adjustable proportioning valve in the rear brake line.If you are advanced enough to need dual masters,you shouldn't need an idiot light to tell you that there is something wrong with your brakes!
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
"Now for my question. If you loose pressure on one side, lets say rear, will the piston shift over and stop all fluid flow, or will it just move over and still allow fluid to pass to the rear circuit."
If you loose pressure, the piston will shift over but will still allow fluid to flow even on the failed side. If you are working on your 70 LT1, it only has a differential valve (NO rear proportioning). As others have suggested, you may want to install an adjustible prop valve in the rears.
If you loose pressure, the piston will shift over but will still allow fluid to flow even on the failed side. If you are working on your 70 LT1, it only has a differential valve (NO rear proportioning). As others have suggested, you may want to install an adjustible prop valve in the rears.
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 2,812
Likes: 4
From: Gig Harbor Wa
Originally Posted by tfi racing
If you are putting in dual masters you probably will want to put in an adjustable proportioning valve in the rear brake line.If you are advanced enough to need dual masters,you shouldn't need an idiot light to tell you that there is something wrong with your brakes!
I mostly wanted to keep the block for ease of plumbing. I already have all new brake lines and would like to replace as few of those as possible.
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 2,812
Likes: 4
From: Gig Harbor Wa
Originally Posted by Duke94
If you loose pressure, the piston will shift over but will still allow fluid to flow even on the failed side.
Last edited by 70 LS1; Apr 4, 2006 at 10:19 AM.
