Classic/Antique Car Repair: 1965 thunderbird power brake booster removal, power brake repair

Question
dear Robert

our 65 thunderbird has power brakes but they don't seem to work. we have narrowed it down to the power booster, but we don't know how to remove it. we asked my fathers mechanic and he said that there are 4 bolts underneath the dash above the brake pedal but we can only get at the first bottom two. yet also underneath the hood, behind the booster there are four nuts that you can loosen. we are wondering if those nuts are attached to a bracket that goes into the fire wall and mounts on those four bolt above the brake pedal. another question is that if we could take the four nuts off of the back of the booster and take it off there. but from the diagram we have of it looks like that there is a diaphragm that goes through the bracket and would attach to the pedal, thus creating a vacuum and shooting the fluid through the lines when applied. we didn't know if it would be okay to take off the nuts from the back of the booster and ten take it out and replace it or if it would even come out by doing that. thanks

Answer
Hello Matthias,

From reading your question, I think you may have already answered it! In general, brake boosters are attached by the 4 nuts you see on the firewall. The diaphragm you mention from the shop manual is actually the linkage between the pedal assembly and the booster. The booster itself is a sealed unit--if you hear vacuum leakage here, it's the diaphragm itself, not the rod. In fact, the actuator or pushrod is not part of the booster itself and doesn't seal anything.

Just to clarify, the power brake diaphragm does not pressurize the brake fluid--this job is still done by the master cylinder. Rather, the diaphragm gives a power assist to help maintain a maximum pedal pressure to the master. In fact, power brakes were only introduced in the 1950's and were originally marketed for the elderly and people with disabilities. Not to mention bigger cars and drum brakes susceptible to fade made this a desirable option even for regular folks.

Hope this helps and good luck!

Bob