single reservior master cylinder

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my66fish

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I need help please. I have replaced my master cylinder in my 66 Barracuda, and I have replaced it with the original style single reservoir master cylinder. I have asked many people and no one seems to know what the brass screw is for and what the function is at the bottom of these master cylinders. Please note I will not use a dual master cylinder as a replacement. My car is an old school hot rod and will remain this way. The problem is for some reason where this brass screw is there is a minor leak and not sure if this is suppose to be sealed or is this suppose to drain excess fluid if the bowl has too much fluid. I'm really not sure what the purpose of this area of the master cylinder. I was hoping to get this clarified before I pull out this master cylinder and return it. For all I know this may be normal?
s-l300.jpg
 
i am interested to know that as well. Mine weeps, especially after driving in the mountains
Maybe that was how it was made before the clamp style. Pressure and a hole. . .
 
Most likely 1/8 NPT thread for a pressure activated brake light switch in a different application of the same master cylinder. Your switch is on the pedal which is a better setup anyhow.
 
dope it and tighten. Should not leak. If the plug leaks, throw a switch on there to plug it. Tandem MC is pretty easy to adapt. I got my old 65 MC, you can have it. didnt leak.
 
That screw is whats holds the piston in the M/C. to remove the piston, you first remove that screw.
 
my66fish said:
I need help please. I have replaced my master cylinder in my 66 Barracuda, and I have replaced it with the original style single reservoir master cylinder. I have asked many people and no one seems to know what the brass screw is for and what the function is at the bottom of these master cylinders. Please note I will not use a dual master cylinder as a replacement. My car is an old school hot rod and will remain this way. The problem is for some reason where this brass screw is there is a minor leak and not sure if this is suppose to be sealed or is this suppose to drain excess fluid if the bowl has too much fluid. I'm really not sure what the purpose of this area of the master cylinder. I was hoping to get this clarified before I pull out this master cylinder and return it. For all I know this may be normal?
s-l300.jpg
Click to expand...


Old school hot rod or not, if you are driving it on the street SAFETY FIRST!

Unless it is a 100% correct restoration, museum piece, in my opinion you should upgrade. Not only for your safety but everyone that you drive around.

If a child runs out in front of you and the brakes fail would be a bad situation. Either way could turn out bad but at least with a dual master cylinder you have a better chance of stopping if you have a failure.

I doubt anyone would even realize that a 66 didn't have a dual master cylinder unless you told them since 67 it was standard.
 
Thank you for your response. What would you recommend? I do have tape dope and this is what I used to seal the fitting for the brake line. I'm not sure what you are talking about with regards to the switch.
 
Thank you all for your time on these responses. Please note I have had several plymouths for over thirty years and they have always had this type cylinder and believe me I understand safety but I like my cars to be period correct.
 
Question for the 66'ers whoo have upgraded to a dual MC - what did you use and where did you get it? I want to upgrade but there is a dearth of information (especially up here north of the border)
 
If you swap MC's make sure you get the correct MC for Disc or Drum application. I have drum all the way around so BOTH reservoirs are the same size. Disc will have 1 large & 1 small reservoir.
I got mine from Rock Auto -Raybestos # MC36439.I ordered the cylinder for a 73 Dart w/ Drum brakes. Bolted directly onto firewall & looks period correct-no one knows it didn't come from the factory unless you tell them or they are well informed like our members.
My local parts store kept getting one for Discs which I am not ready for yet.
 
I had a 65 Barracuda and ran with a single cylinder for years, never had a problem because I maintained the system. If it goes bad there's always the emergency brake.
 
GONEFISHIN' said:
Question for the 66'ers whoo have upgraded to a dual MC - what did you use and where did you get it? I want to upgrade but there is a dearth of information (especially up here north of the border)
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I went to the Ram Man. He's an expert on brakes.

He's a nice guy and will teach you what you need to know. He spent 20 minutes walking me through my upgrade.

I am converting my 66 Valiant wagon from slant 6 to v-8. I already put 10" drums all around, but found a set of KH disc brakes. He hooked me up with a dual reservoir manual m/c and the proper prop valve.

then I went to Fine Lines to get the proper brake lines...

There are two choices to doing the dual reservoir.

You can use the original prop valve and add a t-splitter, or copy the 67 system. I chose to go with the 67 style system.



Give him a call and he can explain what you need to do and most likely will have the proper combo for you. He's a nice guy and will spend the time to walk you through it....


7200 Winters Street
Fort Worth, TX 76120
Store Hours: 9am to 5pm CST

(817) 429-0105

http://www.theramman.com/
 
philip's66 said:
If you swap MC's make sure you get the correct MC for Disc or Drum application. I have drum all the way around so BOTH reservoirs are the same size. Disc will have 1 large & 1 small reservoir.
I got mine from Rock Auto -Raybestos # MC36439.I ordered the cylinder for a 73 Dart w/ Drum brakes. Bolted directly onto firewall & looks period correct-no one knows it didn't come from the factory unless you tell them or they are well informed like our members.
My local parts store kept getting one for Discs which I am not ready for yet.
Click to expand...

This is not completely correct! The dual res master was not always one side bigger than the other! I have the correct for 1969 A body manual disc MC on my 66 Cuda, and it has the same size res for front and back! for the later style single piston caliper, this is more important due to the large size bore behind the Pistons, which require and store much more fluid than the 4 piston K-H calipers!!
 
I converted my 66 using the one Rick Ehrenberg sells. He also sells a kit that includes the fittings required. It wasn't the cheapest, but it was quick and easy and worked well for me. He's a Mopar guy and includes detailed instructions with most of the stuff he sells.
 
wildcat said:
-- old school hot rod or not, if you are driving it on the street safety first!
unless it is a 100% correct restoration, museum piece, in my opinion you should upgrade. Not only for your safety but everyone that you drive around.
If a child runs out in front of you and the brakes fail would be a bad situation. Either way could turn out bad but at least with a dual master cylinder you have a better chance of stopping if you have a failure.
I doubt anyone would even realize that a 66 didn't have a dual master cylinder unless you told them since 67 it was standard. --
Click to expand...
-- x2
 
I have seen them with and without that bottom plug. Some castings have a boss there that wasn't drilled. First I read of it securing the MC piston. I think it is 1/8"NPT as the front port is. Most likely, it was for a switch or as a "tee" in some cars. I wonder if these MC's were used in non-Mopars too. Chrysler didn't make brake parts.

They usually come with no sealant on the threads, so tend to weep. Most secure is probably teflon tape, the thicker yellow type rated for natural gas. Be careful that people say many cheap Chinese tapes are just white plastic and not teflon. The downside is that when you remove the fitting, you get pieces of teflon tape everywhere. Don't screw too tight or you can crack the cast-iron (how would I know?).
 
Thanks for this info.
I also reached out to Mopar Action and received the same response that this area that is plugged being this was no longer used since the brake light switch is now at the pedal area. The only thing I'm not sure of is he said these were done away with in 1962 but mine was the original in my car and is plugged also my 64 barracuda also had the plug at the bottom. At this point I have pulled the master cylinder and will be returning it to NAPA being it continues to leak even with the Teflon tape.

Rick Ehrenberg NOTES
Your master should actually not have that "screw", that was an earlier design, phased out, after, I believe, 1962. The port was for the hydraulic brake lamp switch. By 1966, all Mopars had moved to pedal-mounted switches, so the boss on the master was left undrilled. The rebuilding companies use, typically, a brass pipe plug (NPT) to seal off that port. If you want to seal it correctly, use Teflon pipe tape on the threads.
 
Never saw the picture that showed what he was talking about. There is a screw to hold the piston in on these M/C. Or am I going nutz?
 
Yes, they do come w/ a screw that secures the piston, at least for shipping. I think that is just on MC's for power boosters (like my 65 Newport). As I recall, you remove the screw and plate before installing. Before anyone diss'es me, I converted all 3 of my old Mopars to dual reservoir MC's, but I don't claim that is essential.
 
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