Master cylinder relief port blocked by piston seal?

[Bryce Mcclintock]

Hi guys just finnished replacing rear wheel cylinders and break linings on my 52 Plymouth,  bleed the breaks and went to check my ajustment on rear drums and breaks were locked on ? So jacked front wheels up they too were locked so ok must be the master cylinder? So long story short using the blunt end of a fine drill bit i found i checked to see if the relief port was clear and as you guessed as i pushed it in i had a squirt of fluid everywhere.  When the pressure was gone i reinserted the drill bit and it apperars the cup on the piston is obstructing the relief port so i backed of the ajustment on push rod to double check it was releasing the piston fully and it still is obstructing the relief port ? Can these seals expand over time ? Or am i missing something also when i got car it has Dot 4 fluid in it as the bottle was still in glove box not sure if that would cause issues ?

[Bryce Mcclintock]

Hi guys just finnished replacing rear wheel cylinders and break linings on my 52 Plymouth,  bleed the breaks and went to check my ajustment on rear drums and breaks were locked on ? So jacked front wheels up they too were locked so ok must be the master cylinder? So long story short using the blunt end of a fine drill bit i found i checked to see if the relief port was clear and as you guessed as i pushed it in i had a squirt of fluid everywhere.  When the pressure was gone i reinserted the drill bit and it apperars the cup on the piston is obstructing the relief port so i backed of the ajustment on push rod to double check it was releasing the piston fully and it still is obstructing the relief port ? Can these seals expand over time ? Or am i missing something also when i got car it has Dot 4 fluid in it as the bottle was still in glove box not sure if that would cause issues ?

[TodFitch]

If you rebuilt the master cylinder then the push rod may not be adjusted to the correct length. I only see mention of wheel cylinders so I guess that shouldn’t be a problem. . . But just to double check, with the brake pedal released is the master cylinder piston all the way back to the stop/clip?

 

There should be a little free play in the pedal before the push rod contacts the back of the piston and then a little more travel until the piston cup passes the relief port. The 1946 to 1954 Plymouth Factory Service manual says you should have between 1/8" and 1/4" of travel (measured at the pedal) before the push rod contacts the piston.

 

[Veemoney]

3 hours ago, Bryce Mcclintock said:

so i backed of the ajustment on push rod to double check it was releasing the piston fully and it still is obstructing the relief port ?

You mentioned you backed off the MC rod to provide clearance. Were you able to pull back the rubber boot on the MC to confirm the piston has traveled all the way back to the snap ring as TodFitch mentioned above. If you check this and it has not traveled back to the snap ring then it could likely be rust in the MC which is common over time with the Dot 4 fluid if it was not changed in a while. Image below is an earlier MC but components should be similiar.

[Bryce Mcclintock]

Ok thanks no i didnt pull rubber boot off to check but ill do that thanks