Flushing Brake and Clutch Hydraulic Fluid, Resetting PDWA to Fix Bright Light/Oil Light Off

I have not flushed the hydraulic fluid since I have owned the car.  Many argue it should be done every year or two to remove absorbed water, which rusts the internal parts, causing premature need to rebuild.   Removing the cap from both master cylinders shows some black in the fluid towards the bottom.  I understand this is either rust suspended in the fluid, or bits of rubber from the hoses.  There are no other symptoms that something is “wrong.”  I also learned about centering the PDWA valve, as my friend vigorously pumped the brakes between bleeding.  The brake warning light comes on bright, as well as the oil pressure light stays off with ignition on, engine not started.  I’ll cover how to recover from this as well.  My hoses are old, and I have braided stainless steel hoses to replace them.  Will do this later.  Was in a rush, and should have done it at the same time.

Here is what I did…

Replace Fluid in Clutch Master Cylinder

Pretty straight forward, just sucked it out with a mighty vac, and then use a carefully rolled shop paper towel to soak up the last little bit, and wipe out the black residue.  I then replaced it with Prestone DOT 3.  Eventually I want to swap over to DOT 5, but I am headed to a british car show and didn’t have time to completely tear down.

Opened bleeder on Clutch Slave

Fluid just flowed freely.  I let it run till it was “new.” And then tightened bleeder.

Bled Clutch Slave

I didnt’ trust the “free flow” above, so….

  • Had a friend press slowly on pedal
  • Opened bleeder
  • Had friend yell when 3/4 of the pedal travel was reached.
  • shut the bleeder
  • Verified clutch action felt right – it did not, so repeated till it did
  • Topped up clutch Master Cylinder with DOT3

Replaced the gasket under the Clutch Master Cylinder Cap

It was missing altogether.  I had one in spare parts.

Replaced Fluid in Brake Master Cylinder

Same as the Clutch, but there are two compartments.  When replacing, made sure to pour fluid into the small, front compartment.  I believe my MC is an aftermarket, don’t know if the OEM MC had such a small space to get into for the front compartment.

Bleeding Brakes – Some Things to Know

  • Bleed from the farthest to closest.  Start with passenger rear, then driver rear, then passenger front, then driver front
  • DO NOT PUMP THE BRAKES between bleeding strokes of the pedal.  It will put your PDWA over to one side.  If you do this, you can recover, just nicer to avoid.
  • On a TR6, it is easier to do this with the wheel off.  Loosen the lugs, and then jack it up, place a jack stand, then  remove the wheel.   To put back, use antiseize, and torque to 80lbs, don’t use an impact wrench or you can mess things up, including warping rotors in the front.
  • Clean or replace the bleeder screws, so the vinyl tube gets a firm seal and no bubbles enter or few do.  Not necessary, but makes it easier.  Some little bubbles may enter from the screw threads.  Ignore these.

Bled Passenger, then Driver Side Wheel Cylinders

I tried using the Mighty Vac to suck the brake fluid through, rather than pump the brake.  Didn’t work.  Sequence is Passenger Rear, Driver Rear, Passenger Front, Driver Front.

  • Put some clear vinyl hose on the bleeder, have a friend apply slow steady pressure.
  • Tell him to yell when he gets about 3/4 of the way down the pedal travel.
  • Loosen bleeder till friend yells, tighten.
  • Have friend let pedal up.  Don’t pump it!
  • Repeat until no more air/bubbles.
  • Replace wheel, go on to next wheel.

Resetting PDWA valve.

Here is information about this valve, and how to rebuild it.  http://www.74tr6.com/pdwa.htm   http://www.buckeyetriumphs.org/technical/Brakes/MCPDWA/MC.htm

You don’t need to rebuild it just because it needs resetting, but it is an interesting read.  There is a procedure in the Haynes manual that I followed.  Basically I bled the drivers side front again, slowly, watching for the brake warning light to dim and the oil light to come on.   This did not help.  So I bled the passenger front the same way.  This made the brake warning  light go dim  at first, then it came back on bright.  I tapped the PDWA unit gently with a breaker bar, and it then behaved correctly, oil light too.

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