Triumph Repair: TR6 Brake Problem, brake master cylinder, brake calipers

Question
Hello,

I forgot to metion, I replaced both front brake hoses when I rebuilt the calipers.  If that were the cause; however, why would cracking the brake line at the master cylinder releive the pressure and cause the brakes to release?  This one is making me crazy.  I have searched the web over, with no results.  

Should the master cylinder lines have pressure when the brakes are not being applied?

Thanks again for your help.
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Followup To

Question -
I recently began working on a 1976 TR6 that has been in storage for several years.  I have replaced the starter, clutch master and slave cylinder, and the brake master cylinder, among other things.  

After replacing the brake master cylinder, I bled the brakes and took the car out for a test drive.  I noticed the front brakes dragging and overheating.  After allowing them to cool down and release, I managed to get the car back to the garage.  I figured the front calipers were the cause of my problems, so I rebuilt the calipers and bled the brakes again.  

After another test drive, I notice the front brakes dragging again.  After several short trips and brake bleedings, I was able to determine that after the brakes began to hang, I could crack the brake line at the master cylinder and the brakes would release completely.  I suspected that something was applying pressure to the cylinder, so I drove the car and allowed the brakes to hang, then I removed the two nuts holding the master cylinder to the servo, and moved the master cylinder away from the servo.  The front brakes were still engaged.  Again, I cracked the brake line and the brakes released.    

Is it possible that I have a faulty master cylinder?  Should there be pressure in the brake line at the master cylinder without the brakes depressed?  Any suggestions?   

Thanks for your help.

Answer -
Jeff,

The problem is likely in the flexible rubber brake hoses near the brake calipers.  With age the rubber lining in the hose deteriorates and swells up, effectively closing the hose.  When you step on the brakes you force the fluid under pressure to the caliper.  When you release the brake pedal the fluid can't return to the master cylinder to unlock the brakes.

Keep in mind that if the fronts are bad then the rear hoses aren't far behind.


Cheers,

Jim

Answer
Jeff,

Darn, I thought I had a simple solution for your problem.  I should have picked up on your releasing the pressure up at the m/c line.  

To answer your question, no the brake lines shouldn't be pressurized when the brakes aren't applied.

Under normal operation the fluid enters the master cylinder bore through a small hole from the reservoir.  As the m/c piston travels to apply the brakes the seal passes the reservoir hole, effectively blocking it.  When you let off the brakes the piston/seal assembly should again uncover the reservoir hole, allowing the fluid back into the reservoir, or letting a bit more fluid into the m/c bore (needed as the brake pads/shoes wear).

What is possible is that the new seals aren't an exact match or that the piston isn't coming fully back to rest on the circlip at the end of the m/c.  You say you replaced the m/c.  Was it with a brand new unit?  

If so you might have a chat with the supplier to verify that the unit is correct for the '76 TR6.  And check to see if possibly there was a bad batch of brake master cylinders.


Cheers,

Jim