Master Cylinder Leaking

[RR383]

My new ride the 1970 RR 383 was born with drum brakes all around. I recently purchased this car knowing my first order of business was to replace the master cylinder. I definitely want to retain as much originality as possible. Is a NOS replacement available...or should I opt for an OEM replacement?
I believe the rubber boot has degraded and the o-ring seals internally are shot. Down side the fluid has lifted my paint on the firewall.

 

[Big John]

A NOS replacement would have seals that have dried up from years of sitting on a shelf. As far as originality, chances are probably 99.9% that your master cylinder has been already replaced at least once, so don't sweat that.

Go to your local NAPA store and buy a new master cylinder. The only visual difference may be the cover. An original style cover should look like this:




If it doesn't and your old one does.... swap the covers.

Bench bleed before installing.

If you really think that MC is the original one (again, I doubt it) , another option is to rebuild the MC that is on the car. It's going to be a little hard to find a good rebuild kit as I don't know if anyone has produced them in a long time. Now you are talking NORS parts that has been sitting around for years and probably dried up. It involves honing the bore etc. and most people aren't familiar with rebuilding master cylinders these days anyway. I don't recommend it, just mentioning it and the downfalls.

 

[RR383]

Another look shows the one presently on the car has a single bolt holding down the cover vs. the strong back style in pic. BTW, how do you go about determining whether or not this car has the BIG 11" drum brakes...other than pulling a wheel and measuring the diameter? I understand some did have this feature....

 

[Big John]

If the MC in the car does not have that style cover, then it has been replaced. That IS the OE type cover.

All Roadrunners had 11" drum brakes as standard. If this car is new to you, and you are having issues like a bad MC, I would strongly suggest pulling each wheel and inspecting the brakes.

 

[Ranger]

I just replaced my MC last year due to some pitting in the cylinder with one from O'Reilly and swapped the original cover as shown above. All I had to do was change the bolt.

 

[RR383]

I understand...Where does one find the OE style cover...and by all means I plan on inspecting the entire brake system.

 

[RR383]

Thanks Ranger...you have a B5 car as well. BTW at first glance your running a similar aftermarket intake...what carb is it matched up with?

 

[Big John]

You have a pretty good chance that the new MC will have the correct cover. I'd try that first.

From there, you can either find another used cover somewhere.... They used that master cylinder on about a zillion different models. One will pop up. Keep in mind, that's something you can swap any time and it's more important to get brakes working. Or.... If it bothers you $75 worth, buy one of these: http://www.ebay.com/itm/PG-Classic-236-MCC-Mopar-1970-A-B-E-body-Master-Cylinder-Cover-/371533430725?hash=item56811e3fc5:g:H5QAAOSwd4tUKYP-&vxp=mtr

 

[RR383]

Thanks for the lead...BTW which parts house would be a choice of yours for a new MS....O'Reily, Napa...etc.?

 

[69hemibeep]

A NOS replacement would have seals that have dried up from years of sitting on a shelf. As far as originality, chances are probably 99.9% that your master cylinder has been already replaced at least once, so don't sweat that.

Go to your local NAPA store and buy a new master cylinder. The only visual difference may be the cover. An original style cover should look like this:




If it doesn't and your old one does.... swap the covers.

Bench bleed before installing.

If you really think that MC is the original one (again, I doubt it) , another option is to rebuild the MC that is on the car. It's going to be a little hard to find a good rebuild kit as I don't know if anyone has produced them in a long time. Now you are talking NORS parts that has been sitting around for years and probably dried up. It involves honing the bore etc. and most people aren't familiar with rebuilding master cylinders these days anyway. I don't recommend it, just mentioning it and the downfalls.

John the hold down bolt should be a 1/4-20 X 1.00" Phosphate Hex head grade 5 with an H in the middle .5

 

[Big John]

Thanks for the lead...BTW which parts house would be a choice of yours for a new MS....O'Reily, Napa...etc.?

I use NAPA for a lot of parts.

 

[Big John]

John the hold down bolt should be a 1/4-20 X 1.00" Phosphate Hex head grade 5 with an H in the middle .5

I got your bolt right here Bob.

 

[Ranger]

I understand...Where does one find the OE style cover...and by all means I plan on inspecting the entire brake system.

In my case the cover was OEM. I just swapped the original cover to the new MC.

Thanks Ranger...you have a B5 car as well. BTW at first glance your running a similar aftermarket intake...what carb is it matched up with?

It was a B5 car, but was repainted before I bought it and is now a shade lighter. Hard to tell unless I point it out. I actually like it better and get lots of compliments on it.

I'm running an Edelbrock manifold with an Edelbrock Performer 750 CFM carb (#1411).

 

[RR383]

So your running a 750 cfm carb....and its otherwise a stock 383? And w/o any over-fueling or richness issues. Is this correct?

 

[Ranger]

Well, when I got it, it had a VERY radical cam in it and it was so rich that the exhaust would burn your eyes. So much so that it was no fun to drive, so I swapped the cam out last April. It is a bit more aggressive than factory, but not much, at least that's what the guy I talked to at Jegs told me. I leaned out the carb as much as possible without changing the jets, but my buddy tells me that when driving behind me it smells rich. I probably should look into re-jetting (or going to a smaller carb).

 

[quikbird]

It is very hard to jet it down far enough when what you really need is a smaller carb. 650 should be about right for that engine

 

[69hemibeep]

I got your bolt right here Bob.

 

[droptop]

........All Roadrunners had 11" drum brakes as standard......

Depending on the year. 68-71 yes, 72-80 no.

 

[Ranger]

It is very hard to jet it down far enough when what you really need is a smaller carb. 650 should be about right for that engine

Damn! I was afraid someone would say that. So what's the worst case if I just leave it as is?

 

[Big John]

Depending on the year. 68-71 yes, 72-80 no.

I got your 72-80 right here.... along with Bob's bolt.