I bought a low mileage '71 about 9 years ago.  Shortly after I bought it, I replaced the brake master cylinder.  I probably bought the new brake master at z car depo since that is my usual go to store.

My car experienced a mishap while on the back of a flat bed wrecker truck so I now have some unplanned restoration work to be done.  I was tearing the car down and removed the master cylinder from the brake booster.  Over time, brake fluid has run down behind the aluminum flange and ate the paint from the booster.  The bottom bolt on the booster has light rust on it now.  It didnt before.  

I can't imagine that I did anything wrong during installation.  If the nuts are tight, there isnt too much you can do wrong.  Did I do something wrong or is the brake master bad?  The car probably has 2,000 on that brake master.  Possibly less. I didnt install a gasket but I dont think it had one. I seem to recall a gasket between the firewall and the booster but not between the aluminum flange and the brake master. 

Any advice even if it is wrong would be appreciated.  

Thanks

Your brake master cylinder should not have any gasket between it and the booster. There is no fluid or air pressure passing between these two parts, hence no gasket or seal. You likely have a leaky master cylinder. The rubber o-rings inside the master cylinder can leak, causing brake fluid to exit the rear of the master cylinder, then it leaks through the (non-sealed) mating surface between the master cylinder and the booster. It then dribbles down the outside of your booster and causes the paint peeling you're seeing.

I'd start with a new master cylinder or get your existing one rebuilt. Keep in mind, you have an early 71, so make sure you verify the reservoirs are in the correct orientation on any new master cylinder you get. There was a change in 1973 (i think) that swapped the front and rear reservoirs. For a 71, I believe your front brake reservoir is in FRONT and the rear brake reservoir is in the REAR. in 1973, the designed changed and those were swapped.

Thanks for the help.  I sure wish I would have kept a closer watch on this.  My brake booster was in excellent shape.  Now it is ruined.  😞

Good luck finding the correct master cylinder. I have been trying to restore my original master cylinder (7/71) but have been unable to remove the fwd piston which is stuck inside. This is an off and on again project. Been trying for a year to find an original master cylinder with the front brake reservoir in front with no luck. Make sure you check that the fwd reservoir is stamped with an "F" beneath it, one fellow just switched the reservoirs on top and trying to ply that off on me as an original.

I believe I have a couple of early master cylinders in working order. Definitely used, but should be rebuildable. Message me after the new year and I can something on the way to you if you like.

5 hours ago, Zpenman said:

Good luck finding the correct master cylinder. I have been trying to restore my original master cylinder (7/71) but have been unable to remove the fwd piston which is stuck inside. This is an off and on again project. Been trying for a year to find an original master cylinder with the front brake reservoir in front with no luck. Make sure you check that the fwd reservoir is stamped with an "F" beneath it, one fellow just switched the reservoirs on top and trying to ply that off on me as an original.

Have you tried heat and penetrating oil? I have found if I heat it to 350f or so and put some oil down it, I can push down on the pushrod with a punch to get it loosened up. Then it will tap right out. The aluminum grows faster than the steel pistons.

Rebuild kits is another matter...

35 minutes ago, Patcon said:

Have you tried heat and penetrating oil? I have found if I heat it to 350f or so and put some oil down it, I can push down on the pushrod with a punch to get it loosened up. Then it will tap right out. The aluminum grows faster than the steel pistons.

Rebuild kits is another matter...

Thanks, Patcon, will give it a try. Heated it in a pot of boiling water mixed with WD40, no luck. Tried the freezer, too, without luck.

It can take a good bit of heat.

Your hood up to about 1000d F after about 1200 you get aluminum puddles

A good electric heat gun.

Chuck it up in a vise pointing upward. Add some wd40 and heat it up. I use an IR gun to monitor heat

3 hours ago, zKars said:

I believe I have a couple of early master cylinders used, but should be rebuildable. 

I've looked around for rebuild kits with very limited success. The only rebuild kits I've found that I think are correct are on ebay for big money.

I've been working with another supplier on putting together a correct kit, but no luck so far.

What is the harm with installing the later '72+ version of the master cylinder?  Factory versions of those are still available.  Other than the reservoirs are switched, is there any other difference?

That is what I installed on it previously except it was aftermarket.

I currently have a later version on my car. The brakes work fine, albeit they seem a little touchy. The biggest problem is you that have to swap the front and rear brake lines that go to the master cylinder. This requires physically bending the brake lines.

8 hours ago, Zpenman said:

I currently have a later version on my car. The brakes work fine, albeit they seem a little touchy. The biggest problem is you that have to swap the front and rear brake lines that go to the master cylinder. This requires physically bending the brake lines.

As far as I know, nothing wrong with this approach. I think many folks have had to do this. Kinda a bummer to bend the factory lines, but hey, gotta make it work.