Master Cylinder Push Rod Adjustment Procedure

[plymouthcranbrook]

Having figured out that my problems with brakes on my 52 Plymouth is most likely caused by an improper push rod adjustment I wondered if someone could tell me which way to move the push rod(I.E. lengthen or shorten it) to allow the brakes to return to the correct rest position. I am not sure what is meant by the hole in the Master Cylinder being plugged. I do see the hole, just cannot tell it it is blocked or not. Any advice appreciated.  Thanks.

[plymouthcranbrook]

Then two minutes after posting this I find the tread describing how to adjust it. Missed it before in my searches. Sigh...Old age strikes again.

[Niel Hoback]

Don't feel bad, be happy that you figured it out yourself. Plymouth owners are good at that.

[Joe Flanagan]

I've discovered that it's pretty hard to find a piece of wire thin enough to go into that relief port if you need to clear it out or check it. I used a piece of welding wire from my MIG. 

[Don Coatney]

I don't recall what I paid, when, or where I bought this set but they sure have come in handy over the years.

 

 

[BigDaddyO]

Ask your dentist if he has any old probing tools he wants to get rid of.

I got about 6 last time I asked.

[plymouthcranbrook]

Thanks for the ideas.  Will do the deed next week.

[Niel Hoback]

Strip some copper wire and use just one strand.

[ptwothree]

What you should end up with is about 1/8" clearance between the push rod and the primary piston.  Don't confuse this with the free play at the clutch pedal.  Free play at the pedal includes the push rod clearance.

 

If you have the master cyl. assembled correctly, then you should be good to go. Also, watch out that you don't damage the  cup when probing with the mig wire or whatever you are using.  It can be easily damaged.

[soth122003]

When all else fails, go into the kitchen, make a sandwich, relax for a bit, then use the twist tie from the bread wrapper to clear the port.

[Joe Flanagan]

Now that's ingenuity.

[plymouthcranbrook]

Thanks again for the ideas and advice.

[JR-39D11]

Then two minutes after posting this I find the tread describing how to adjust it. Missed it before in my searches. Sigh...Old age strikes again.

Can you provide me the pointer, I'm looking as well and having trouble finding with my keyword search.

[plymouthcranbrook]

Well,  I thought I had figured out the problem. I adjusted the push rod to get the pedal set correctly and looked into the master cylinder and saw the vent hole.  Appeared to be a round clean hole so I went for a test drive.  Brakes locked up again.  Readjusted the push rod and looked again. Tried to push a very small wire around the hole but seemed to be no place to get any entry to the vent. Looked in the manual but no help there. Can some someone explain to me where this small vent hole is in the larger one? I have adjusted the push rod all the way in both directions to see if I could find a place to start but only succeeded in completely locking up the brakes in one direction and partially in another.   Thanks.

[Joe Flanagan]

I just went through this a couple of weeks ago. The large hole should be obvious. The smaller one is right behind it, toward the rear of the car. Is it that you can't find the hole or that you are unable to get a wire inside it? In my case, I was using a rubber cup in the master cylinder assembly that was too wide and it was blocking the relief port. The result was locking brakes. That might be your problem. When I pushed a wire down into the hole, I could feel the rubber cup, which is not supposed to be blocking that passage. You should only have 1/8 to 1/4 free play in the brake pedal.

[ptwothree]

Watch out when poking around for that seal.  If it gets damage, it will be just about impossible to bleed the system............

[plymouthcranbrook]

A professional mechanic rebuilt and installed the master cylinder a couple  of years ago.  All worked well(although I haven't driven the car much) till I had to redo the front brakes.  All six wheel cylinders and front shoes. Don't have a professional brakes adjusting tool for Mopars but still though it was close.  I will try to see if I can get a smaller wire into the back of the hole. I can see the brass(?) shiny push rod through the first port. I won't be able to work on it till next week(My last sort of full week at the local theme park is starting tomorrow, Ring the bell and blow the whistle on the train). I will report on success or failure then. Thanks all. 

[plymouthcranbrook]

I just went through this a couple of weeks ago. The large hole should be obvious. The smaller one is right behind it, toward the rear of the car. Is it that you can't find the hole or that you are unable to get a wire inside it? In my case, I was using a rubber cup in the master cylinder assembly that was too wide and it was blocking the relief port. The result was locking brakes. That might be your problem. When I pushed a wire down into the hole, I could feel the rubber cup, which is not supposed to be blocking that passage. You should only have 1/8 to 1/4 free play in the brake pedal.

I just re-read your post. I see two holes, one slightly larger that the other  with the bigger one toward the front of the car. The one I have been trying to open is the one toward the back of the car. About 1/16th of and inch or so in diameter. I see a clear hole but there doesn't seem to be any opening in the bottom of the hole. Appears to look like mildly rusted steel. Is there another one I am missing? Or is the smaller hole somewhere inside the bigger one.  As i said, this master cylinder was redone about 500 or so miles ago. This is why I am surprised to have this problem. All fluid is new earlier this year. Clean and clear.

Edited August 21, 2014 by plymouthcranbrook

[Joe Flanagan]

Sounds like you found it. The one toward the rear of the car is the one you're looking for. The opening is very small. You might be using a wire that's slightly too large. I used a piece of wire from my MIG welder, which I think is .030 or .035. You can also use the wire from a twist tie (so I understand) or strip a strand from a copper wire. What condition are your hoses in? They can also cause this problem.

[Dodgeb4ya]

The rear M/cyl hole is extremely small at the bottom-maybe .015".The top portion of this hole is much wider than the bottom portion of the hole that goes all the way through into the piston bore.

 

Use a piece iof single strand copper wire pulled out of 16ga, regular automotive copper wire. Or as mentioned a twist tie wire. Something very small and not very stiff to poke through the hole. The wire should easily poke right through down into the piston bore. Pump the pedal and recheck several times to be sure.

[plymouthcranbrook]

Hoses are almost new. Is the hole at the front or rear of the bigger one?

[Joe Flanagan]

The hole is at the rear of the bigger one. Two different holes. If you push the brake pedal with your hand, you should see fluid flow up out of the small hole. That was not occurring with mine, which told me the hole was blocked somehow. Thus the dragging brakes.

[plymouthcranbrook]

The hole is at the rear of the bigger one. Two different holes. If you push the brake pedal with your hand, you should see fluid flow up out of the small hole. That was not occurring with mine, which told me the hole was blocked somehow. Thus the dragging brakes.

Thank you. That is what is happening with mine.

[Joe Flanagan]

I would say that maybe the person who rebuilt your master cylinder unknowingly used a rubber cup that is too big, but since you said the brakes were functioning before you did the recent work, I guess that can be ruled out. Do you know if it's just your fronts that are locking up?

Another thought is that maybe that cup got kinked when you reassembled the master cylinder. 

Edited August 21, 2014 by Joe Flanagan

[plymouthcranbrook]

All four wheels lock up(not tight, just drag). Master cylinder was installed by the man who rebuilt it.. I am going to try to locate the small hole next week after work weekend is over. Will report back then. Thanks again to all who have posted. Can't say that I won't have to remove the cylinder, just hope not to have to.

Edited August 21, 2014 by plymouthcranbrook