Select a Vehicle

Find parts for your specific vehicle

Choose your Vehicle

Having trouble finding a specific product?

1970 Mark III Power Brake And Vacuum Issues

Hi Bill –
I just purchased a 1970 Mark III and after a week of learning and hassles, I have finally got Urzula back on the road. I have replaced the original intake manifold and carb with a new Edelbrock setup, but now I am having a couple issues. Most importantly my brakes have lost, seemingly, the power assist. I have checked vacuum going to the booster and while it is present I don’t know how much vacuum is there. I now have it directly connected to the rear port of the carburetor. Furthermore I was negligent in my documentation and could very well be completely missing a vacuum hose. I have consulted the 1970 shop manual and can’t make out the problem. When I step on the brakes, there is a “heavy clicking” for lack of better description, while depressing the brake until it starts braking. Phew. Hope that is enough for an idea, and some much needed help!
Hi Scott –
After reading your post a few times it seems as if you have lost power brake assist after you have replaced the intake manifold and carburetor. The power brake booster needs to receive a large volume of vacuum as provided by the original style intake manifold and carburetor. The vacuum required is such that if you disconnect the supply hose to the booster with the engine running at idle the engine will stall or run extremely rough. Since you seem to be unsure of how much vacuum you now have available at the booster, I think that you should pursue that avenue first. If the power booster is not defective but the vacuum to it is found to be low you then may need to consult with the supplier of your new non original manifold and carburetor in order to find out how to supply the needed vacuum to the booster with their manifold. We are familiar with mostly the factory designs in that regard. They may even have some sort of adapter available for this purpose if your present booster vacuum is insufficient. If your shop manual is the factory 1970 FoMoCo shop manual there is a section in Volume one that describes a booster test. If it happens that you need further booster help or replacement please call our office and ask for Al.

Have a Question? Submit your question to Bill!

Submit your Question

Your Selected Vehicle