TR6 TR6 Brake Master Cylinder problems

[bailee2]

Had my Master cylinder and PWDA valve rebuilt in time for the Polar Bear Run today and spent the last day and 1/2 bleeding and troubleshooting (using CastorOil LMA). Result: No Triumph for the Run today.
Problem:
Master Cylinder started leaking and removing paint so I sent it in for repair with new sleeve installed and had the PWDA rebuilt. After rebuild I bench bled and ran new fluid in the system.
Brakes have no signs of air using manual and vacuum bleed methods after two serious bleeding attempts. Yet only 1/4th of pedal has brake action.

Brakes seem to have no pedal until it is 3/4th stroked in and seems to get better at the last 1/4 of pedal stroke.
Centering PWDA Valve had no effect during/before bleeding.
Master cylinder strokes all the way in and pushes fluid before installing and will push fluid through the wheel cylinder bleed ports until it is clear of air.
Brakes are not safe at this point and I now need to problem solve.
New Front Calpers, Slotted Rotors, brake shoes/wheel cylinders and lines were installed which all worked ok before MC was rebuilt.
Ideas?
Thanks in advance!
1972 TR6
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[hondo402000]

I had the same problem when I installed a new MC and brake booster, when you pull the MC off the booster there is a small, like 9mm ball type nut and screw on the booster, if you screw it out it hits the MC sooner when you push the brake peddle down, be careful to screw it out only one turn at a time and then check your brake peddle, I screwed mine out too far and testing the car and brakes around the block the MC internals would not come back far enough in the MC to release pressue and the break stayed on aka locked up,
try that, hope it helps

 

[TR4]

You might need to also bleed the Slave Cylinder after all your work done. Air may have gone down that hose. I had to remove my slave and let it hang while bleeding so all the air could flow up and out of it.

 

[TR3driver]

I agree with Hondo, check the freeplay between the booster & the MC. ISTR it should only be .010" or something like that ... not zero, but not much either.

 

[LastDeadLast]

I agree with Hondo, check the freeplay between the booster & the MC. ISTR it should only be .010" or something like that ... not zero, but not much either.

This is interesting.. what would be the easiest way to check the freeplay?

 

[hondo402000]

not sure I can help you with that, for me is was screw it out one turn, check the brakes for feel, test drive, pump the brakes and usually one trip around the block I could tell if the brakes were locking up, if so screw the little bolt in one turn and try again, there might be a more scientific way but the procedure worked for me

 

[BOXoROCKS]

...did you install a new booster????? and why??? Have you checked all clevis pins and forks? Get some old brake line fittings, braze the ends shut. put them in you new MC.bleed the MC 1 fitting at a time. Bench bleeding doesnt always get the job done. Anyway, after you have redone the MC then work you way down stream. you will get it right with this method. its just plumbing, and we all know plumbers only need to know two things, sh*t don't run upstream.....and payday is on friday.

 

[hondo402000]

I have read through the bently book and another service book and is says nothing about how to adjust the servo unit, really disappointing that there is an adjustment nut on the end of the number 17 Hydrolic push rod in the Servo unit but never mentions how to adjust it, or check set for clearance. Guess its one of those secret things the dealer would only know,,, again I refer to my above post for how I did it..... but I noticed a big difference when I screw the nut in or out 1 turn

 

[BryanC]

The Haynes manual has a section on adjusting the hydraulic pushrod. In summary, it says start the engine and adjust the position of the bolt head so that it is 0.001 to 0.016 inch below the face of the front shell.

Bryan

 

[TR3driver]

According to the TR5-TR250-TR6 Owners Workshop Manual from Brooklands, the gap should be .011 to .016" (which seems more reasonable to me).

 

[hondo402000]

I think I will check mine this weekend and see how close I am, I didnt think about starting the car though, but makes sense that a vacuum on the unit would change the clearance

 

[LastDeadLast]

Hondo,

Thanks to you have have awesome brakes now!!!! I removed the MC and sure enough, the booster wasn't adjusted properly (according to the Haynes manaual). I made the adjustments and WOW, what a difference.

Thanks again.

 

[hondo402000]

hey Shannon, glad it worked out!