leaking master cylinder cap.

[72bluNblu]

Just wondering, what is the reason for pointing the vent toward the rear?

The top of the plastic reservoir is not flat, it has an angle. If you point that little vent to the rear, it sits higher than if you point it to the front. So it’s a little less likely to seep fluid in that position.

It’s a minor difference, but having run them both ways it seems better with the vent to the rear. It’s also a really easy thing to do, so even if it only makes a small difference why not do it? Easy and free.

 

[mrhp]

Appreciate the explanation. Makes sense.

 

[KJoeZ61]

I bought the same MC from Dr Diff and had the same problem. Bought new yellow caps from Autozone and problem solved. With that said I have no regrets about buying the MC from DR Diff, great improvement!

 

[mrhp]

I bought the same MC from Dr Diff and had the same problem. Bought new yellow caps from Autozone and problem solved. With that said I have no regrets about buying the MC from DR Diff, great improvement!

Saw those yellow caps (Mopar Part 04683656AB). Why are they so expensive compared to the black caps?

 

[KJoeZ61]

Maybe that’s why, but they don’t leak.

 

[mrhp]

Interesting. Curious: Why would the yellow caps be better or different than the black caps? Seems like the black caps were OEM on older Mopars and the yellow ones on the newer. Other than the color, how would the construction or gasket be different?

 

[72bluNblu]

Interesting. Curious: Why would the yellow caps be better or different than the black caps? Seems like the black caps were OEM on older Mopars and the yellow ones on the newer. Other than the color, how would the construction or gasket be different?

Hard to say what's different, the yellow caps don't seem to have that molded in "bump" for the vent but other than that they appear similar. I haven't run the yellow caps though so I haven't compared them side by side. They could have a different venting system, thicker gaskets, darn near anything. Everything Mopar is more expensive, there is a crown automotive version of those yellow caps for $9.99.

For what it's worth, the Mopar yellow caps are listed as 1995-2020 caps. The black Dorman caps I listed earlier are listed for 1978-1994. So technically for the master cylinders we're running the black caps are correct and the yellow caps are not. But like I said, I haven't tried running the yellow ones.

Here's the yellow ones
Mopar (20.99!!!)
Mopar Replacement 4683656AB

Crown (9.99)
Crown Automotive 4683656 Crown Automotive Master Cylinder Caps | Summit Racing

 

[cruiser]

I've found that for the cast iron OEM masters, the gaskets that are available are thinner and of a more 'plastic'-y material. When I was still running the OEM master on my '70 Dart I found this one from IH is just like the factory 'originals' in thickness and composition: Disc/Drum Brake Master Cylinder Cap Gasket for 1974-80 Scout II, Terra or Traveler - IH Parts America . It solved the leak problem.
Often the same casting masters were used across a variety of vehicles and you can search for a gasket by the casting number.

The remanufactured factory original master cylinder for my 1974 Duster leaks a bit. Do you think replacing the gasket with this IH part will solve the problem? Thanks.

 

[mrhp]

I think the ‘74 master is a little longer. If so this particular gasket would be different. If you look up the Bendix casting number for your master you’ll be able to match up the correct gasket.