Leaking Master Cylinder? Rebuild it? Replace Master Cylinder and Booster?

[1970 RT Challenger 1970]

Are you better off to replace all or use a rebuild kit?

Both Discs and Drums seem OK for Leaks.
No Leaks inside firewall inside the car.
There are Leaks down the Booster and popped the cap on the master cylinder and the primary side (Rear Reservoir) was down lots.

Are Napa Parts good? They have a new made Master cylinder and a rebuilt Booster for a 440 and Disc/Drum.

Thanks

[Supercuda]

NAPA parts are fine, and the availability of a complete setup makes replacement virtually troublefree. The only drawback is the loss of date-coded, original parts. This is only an issue if you desire originality. Option I would use is the replacement of the worn parts, and keep the old ones just in case.

[Bullitt-]

Rebuilt MC may be a crap shot...the one from NAPA I received has issues, 1st it was a style for a later model, the top although painted was pitted badly, one of the line connections was stripped.    Even though it actually cost more I rebuilt the one that was on the car as there were no issues with it...  The new ones are not a bad option IMO if your not doing a concours restoration but I'd save the old one for some day if it is correct.

[Chryco Psycho]

if ti works ok now & you can get a kit rebuilding it is easy to do
or just buy a rebuilt one & install it

[Justins72]

We are learning general brakes and leaking master cylinders In school right now (wyotech). The rear part of the master cylinder resivor deals with the front brakes. It sounds lime you might have an external leak somewhere in the front due to the onside being down a lot. What does the pedal feel like when coming to a stop? If it stops fine at a light or sign and while the brakes are applied if the pedal continues to slowly move down then that would be a leak in the master cylinder, primary cup seal to be exact. I would carefully check all lines,hoses, the metering valve first

[1970 RT Challenger 1970]

The outside of the master cylinder is somewhat wet/damp with brake fluid, an oily look,  as when you put your gloved hand underneath it, it's wet. You can see where the brake fluid ran down the Booster. Also some peeling, bubbled paint on the Booster/MC.

It still feels normal when braking, no pulling.
When you pump the brakes with the engine off, I'd say after 2-3 pumps the pedal gets stiff or hard to move, pretty much like any other car with PB.

Happened to notice it when doing the oil change and other routine checks.

Thanks for all the replies.

[Justins72]

Were you able to see any cracks by the empty resivor? There are only a couple places a master cylinder can leak. Either there's a crack, the seal behind were the rod goes into to master cylinder (behind were it bolts to the booster),the resivor cap if the fluid got hot enough to boil and the seal was bad, or were the lines attach to it. If it's leaking from the back then it can be rebuilt, if its crack then needs to be replaced.

[Justins72]

But from what I have read it most likely needs to be replaced.

[IMNCARN82]

Sometimes the gasket on top isn't held down tight enough by the small rod.I've pulled them off and bent them down to apply more pressure sometimes. They will leak if over full. Make sure the locating tabs are in place on the gasket too.  NAPA is fine. Beats Chunker.  I need to replace mine too. 

[Justins72]

Above poster is correct, just to add never fill the resivor to full needs room for expansion when it absorbs condensation. When you fill it leave a 1/4" from the top.

[1970 RT Challenger 1970]

Sometimes the gasket on top isn't held down tight enough by the small rod.I've pulled them off and bent them down to apply more pressure sometimes. They will leak if over full. Make sure the locating tabs are in place on the gasket too.  NAPA is fine. Beats Chunker.  I need to replace mine too. 

I got a friend to pump the brakes with the engine running while I watched the master cylinder. Brake fluid ran down the sides of the master cylinder from below the cover. I tightened up the spring over 3 trys, and it might be fixed, but there may be another cause.
How much play should there be on the master cylinder lid or cover when it is sitting on the master cylinder without the spring on? - as I have about 1/4" to 5/16" when you move the cover front to back and left to right. I think the cover is oversize and maybe from a bigger master cylinder?

[Supercuda]

Your cover sounds about right. These were routinely sloppy in fit, and this is because they needed to be easy and quick to install. Later m/c covers were designed to address the "spillage" that occurs as the brake fluid splashes around in the m/c. The later Chrysler reservoirs have tight-fitting, threaded caps. Later GM reservoirs have tight-fitting, snap-on covers (real messy to remove!). Best practice is to leave the reservoir low enough that it doesn't splash as high in the reservoir, keeping splash and spillage to a minimum.

[1970 RT Challenger 1970]

How high from the top of the reservoir would you fill it. On the back reservoir it's 1/2" from the top and at the front reservoir it's 1/4" from the top.

Who sells correct Boosters and Master Cylinders for 1970?

I see Jim's Auto Parts has them. Summit has a Generic type and Billet Aluminum from SSBC. Yearone.
Are the Raybestos M.C. pretty decent? What about rebuilt Cardone Boosters?

Anyone else sell them?

[MEK-Dangerfield]

1/4" from the top is fine for the brake fluid. I just want to ask if you have replaced the rubber gasket under the cover? Maybe it's old? It took me a couple of tries with messing with that spring on the lid to get mine not to leak.     

[1970 RT Challenger 1970]

Thanks ,I'll give that a try as well - replacing the rubber gasket.