TR6 newcomer needs help tr6 brakes- sorry long post

[matscar]

did not use my car for 3 weeks and found a spongy brake pedal and the dash light on pedal pumped up again but have several questions
1.how do you reset the hydraulic switch if its stuck and are they available new-mine seems gummed up.
2.the light stays on even if i disconnect the wire from the switch.
3.there is only 1 wire going to the switch but it has 2 terminals.
4.If the MC is leaking backwards into the booster where would i find the fluid going-i must have a leak but cant find any fluid.
Thanks for any and all help

 

[Keoke]

Matscar, Ill try question #4. If fluid leaks into the brake booster you will find lots of white smoke coming out the exhaust because it has been sucked into the intake manifold via the Vac line. ---Fwiw--Keoke

 

[Mark_Gibson]

Re: newcomer needs help tr6 brakes- sorry long pos

Matt,

You need to get ahold of a Bently shop manual for your car. It will explain how to reset your PWDA switch if it gets off center. The reason the light stays on is that the switch is normally closed (grounded) with the PWDA off center. When its centered, the spring loaded switch extends and opens the circuit, extinguishing the light. If you unscrew the switch from the housing, you will see how it works. You must have one circuit (forward or rear) with low pressure, as the purpose of the PWDA is to keep fluid in the undamaged portion of the system in the event of a leak so that you at least have partial brakes. The other place the booster might leak is into the drivers compt by your pedals, Check there for any brake fluid. You should be able to tell which part of your brakes (front or rear) are leaking by looking into the master cylinder reservoir to see which side is low. The front and rear brake reservoirs are seperated by a divider inside the MC reservoir.

Mark
1970 TR-6

 

[Yellowdog]

Re: newcomer needs help tr6 brakes- sorry long pos

As for the one wire / two terminal question, depending on the year of your car it was wired using two methods. One was a single wire that fed from the harness between the oil pressure and brake lights and grounded through the switch/PWDA. The other used two wires with the switch being wired in between the oil and brake lights. I believe the double wires were started in the '74.5 model but would not swear to it. Actually, it would not matter how it is wired as the end result is the same. Besides, the two terminals on the connector are common inside the switch.

I doubt that your switch is gummed up as it should not have come in contact with any brake fluid. This switch rides on a tipping valve inside the master cylinder. When the valve tips, the switch activates. The tipping valve is designed to fit in a detent in the MC plunger in such a manner as to prevent fluid from being sent to either the front or rear brakes if there is a loss of pressure in one system.

To further Mark's comments, until the problem is repaired and you can re-establish pressure on the 'weak' side, you cannot reset the tipping valve in the master cylinder.

 

[matscar]

Re: newcomer needs help tr6 brakes- sorry long pos

thanks for the info-i meant to say the movable piston in the pwda is gummed up and stuck off center,are the seals in it replacable or should i get a new one. Also the warning light stays on even if i disconnect the wire to it=im guessing this means i have a short to ground prior to it.

 

[Mark_Gibson]

Re: newcomer needs help tr6 brakes- sorry long pos

Matt,

The seals are replaceable, tho its a delicate job. The only reason the light is staying on is that the switch is doing its job. If you were to remove the switch from the PWDA assembly (it secrews off), connect your lead wire back to it (either terminal); the light should be off. Once you unscrew the switch, the plunger will be extended and thus extinguish the light. If you press on the plunger the light should come on. You can purchase a rebuilt PWDA, but they are pricey. My friend Mark at British Auto can rebuild yours (basically disassemble it, clean and replace those rubber O ring seals) at a fraction of the cost of a new one, his number is 800-458-4575. Good luck.

Mark