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Triumph Repair/1970 spitfire brakes

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Question
Hey Howard, I replaced everything on my 79 Spitfire brakes.  I have bled and bled and can't get a good pedal.  I read your 2009 help you provided to a guy with a 76 spit and I have all of what you recommended to do and I will look into all of that tomorrow.  However, could you give me just a little more insight as to what the PDWA actually does?  I understand that if there is a pressure difference between the two circuits, the little valve thing slides left or right thus lifting the little nipple on the switch and turning on the light.  When I bleed my rear brakes for instance, doesnt that fluid release trip the PDWA and move the valve?  I actually have my switch out and use a mirror to look inside.  I can see when the groove is not center and I insert a screwdriver and force it back to center.  Question.......what recenters the valve if I didn't do it.  Question........if the valve is left or right, does it cut off fluid flow to either circuit.  I ask because I'm curious if the front or rear fluid circuit is blocked when the valve is not center thus restricting bleeding efforts.  One fella told me that mechanics used to grind a bolt the size of the plastic switch threads to a point and insert it in the PDWA to hold it center during bleeding.  As always Howard.....thanks so much....Rory to a point

Answer
Hi Rory,

That thing is just a warning light to tell you one circuit has more pressure then the other does.

When bleeding the brakes the warning light will come on as the pressure is high on one circuit and not on the other so the piston moves over and that grove operates the switch. The factory procedure is to have someone to open the bleeder on the other circuit while you slowly press on the brake pedal until the light goes out and you have to remove your foot off of the brake peddle quickly or the piston will go too far and set the light off again on the other side.

I have not heard about making the holding device for when bleeding brakes but it sounds like that would work as long as when you are finished bleeding both circuits are ok then it will stay centered.

This light system assumes the driver is not to bright and don't know he has a soft brake peddle or half the peddle he is suppose to have.

Howard

Triumph Repair

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Howard M. Fitzcharles III

Expertise

Triumph TR-4 up & Spitfire, and Engine theory

Experience

Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Organizations
Associate member SAE EAA member

Publications
Import Car magazine

Education/Credentials
ASE Master Auto with L-1 certification up to 2000

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