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The special tool is designed to be inserted in place of the porportoning valve's switch. It holds the internal piston by the indent in the piston where the switche's plunger pin usually rests.
The piston will move to activate the switch by pushing the switche's pin up and closing the curcuit to ground and illuminating your brake warning lamp in the spedo cluster. This lamp will also light when the emergency brake is pressed down and it's switch grounds this same circuit. The lamp carries a positive current so either switch will light the lamp in the spedo cluster.
The porportinging valves piston only moves during a brake line failure during which there is a great dis-porportion between the pressures of the front and rear lines.
I have been told that when bleeding your lines (starting from the rear) it is a good idea to occasionally bleed the fronts during the process so that there will not be too much pressure applied from the rear lines that might move the portortioning valve's piston. That is the the insurance the tool gives in this case.
I have also been told that using a vaccume pump to blead your lines eliminates the danger of the piston in the porporioning valve from moving.
Van at
Vanco Power Brake Supply
9738 Atlantic Avenue South Gate, CA 90280
(323) 563 1588 [email protected]
Can remaunufacture your bad porportioning valve for $ 75.00
This saves a LOT over buying a new one.
Usually a 15 year old valve can use a rebuild anyway as there are quite a few seals in them to deteriorate.
Good insurance due to the importance of your brake system and to your own safety.

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