I need help diagnosing a brake issue on my 69 Delta. While stopped at a light I feel a very slight falling away of the brake pedal. If I pump the brake it stiffens right back up. It was so slight I was not sure it was happening. Over time however I am convinced it is. Also, I am not sure I am getting optimum braking power but have a tough time relating the power of the Olds brakes to more modern cars.

Second, last night I parked the car in the garage. After turning it off I realized I needed to pull the car further into the garage (occasionally I envy you A body guys). I fired her up and moved forward 6 inches or so. When I hit the brake it went all the way down. I let it out and hit it again and had firm braking power. Perhaps a vacuum issue??

Background: I have drum brakes all around with new shoes and wheel cylinders a couple of years ago. The master cylinder is currently full (I have checked it frequently after these issues) and there are no leaks that I can see but I have yet to pull the drums off. The power booster was replaced a couple of years ago as well. The current master cylinder was put on by a previous owner many years ago and is not stock.

Thoughts? Looking at my chassis manual makes me think I may have a bad master cylinder.

 

I would say your master cylinder is bad.

 

^^^^^^^^^^What he said. Unless you can see a puddle of brake fluid on the floor, this is the classic symptom of a bad M/C.

 

Great guys. Thanks for the feedback.

I assume that the new MC needs to match the power booster (Bendix or Moraine). I don't know who made the booster?? It is silver, probably a reman unit. 1) does the MC need to match the booster? and 2) if so, how can I tell what I have.

 

I believe there are 2 types of MC's as you state. Take your old one with you to be sure. If I remember correctly there is a different length brake pedal rod and perhaps diameter rod needed between the two. The booster will be the same.

 

bcg88: You definitely have a bad master cylinder. To be sure you get the correct part, take your old master cylinder with you. Sometimes discount chain auto parts stores (like AutoZone, Advance, Checkers/Schucks/Kragen/Murray's) list the Moraine for automatic transmission vehicles and Bendix for manuals (although this is not always the case). Best of luck!

 

Thanks for weighing in! After due diligence, I ordered one off Rockauto. It came yesterday and matches my current setup. I will install tomorrow. wish me luck!