About 4 years ago, had a chrome master cylinder on my '78, but had the original black brake vacuum booster.  I found a chrome booster so I had the mechanic install that along with the (I am soo dumb sometimes...wadda you mean SOMETIMES) the fitting that brings the vacuum from the base the carb to booster, with a chrome fitting.  After that replacement, I did not have much brake pedal, it went a loooong ways before the brakes would engage.  The mechanic claimed it was the booster.  The 2nd mechanic said the pistons in the master cylinder was 'bypassing".  I had a new (and really cool looking) master cylinder installed last week with this new mechanic.  It did not solve the bake issue totally.  It is better, but not as good as it used to be. 

Changing a brake booster on these cars is a study in patience....and the use of foul language. Getting to the four nuts that hold the booster on is a major pain, even with the correct tools. If you enjoy hanging upside down under the dash of your Shark for a few hours, then you might have a blast. Removing  and re-installing the small clip that holds the linkage rod to the pedal can also turn your day into a nightmare, unless you have really tiny hands, and eyeballs that can see around corners.....

 You can take the master cylinder loose, and gently move it out of the way, and not have to break loose any brake lines.

In other words, yes, it can be done by those not mechanically inclined, but it can be a real test of your determination, the amount of skin on your hands, and how large your swear jar is.....

Thank you Dr. Adams.  I am a 6'-1" and not tiny, so I do not fit under a dash...right-side-up, up-side down sideways or any ways.  Clint could fit.  Clint is so fit and trim, that I could fold him up and have him work on it from inside the dash!  I naively thought that it was four bolts, a linkage and presto! 

I do not think easy is a reconized word when it comes to the C3. I saw a booster replaced at the MAMO gathering....it was not pretty! (and Joel was there)

Mr. Ebo,

You need the best tool for going under the dash to do a booster......Barb Shimer!!

I replaced my Booster & M.C. at the same time in my driveway.

I took the seat, steering column and clutch and brake pedal assembly out to give me room to get to those PITA booster nuts. That was not a fun evening.

The check valve on the brake booster is basically a one way check valve.
Pull the hose off the engine side and try to blow into the end of it. You shouldn't be able to blow through what so ever.
Then try to suck air through the hose. You should be able to draw so air through. If not, gently wiggle the check valve out of the grommet on the booster and try it again. There may be stored vacuum in the booster already. If you do have to wiggle the valve out and you hear a hissing noise that will tell you the booster and valve are working to hold vacuum. 

|UPDATED|9/10/2012 7:22:15 PM (AZT)|/UPDATED|

I did drive the '78 to work yesterday to experiment with the brakes.  I do have more brakes then before the master cylinder replacment.  When I press on the pedal, I cna tell it is an immediate reaction.  I get to the place where I figure I should be sliding the tires and the pedal just travels more.  I am kind of wondering about the rubber brake line.  I have heard that they can become soft over the years, and then expand when having pressure put on them.  I know a lot of autocrosser's that change out the rubber to stainless just for that reason.  As far as I know, the rubber brake lines have never been replaced.  Might that be where some of the "sponginess" feeling is coming from?