Sticky brake pedal

[Ron H]

I had the same problem with these after market generic boosters. The comments above are correct. It is the heat on the booster that causes the seal on the bakelite piston on the input rod to get tight. This is because they hang off brackets from the firewall and are more exposed to engine bay heat - in particular the back of them.
Changing the booster and master cylinder set-up back to factory solved my problem.
Why does that help? Because the booster is mounted directly to the firewall and the back of it is not exposed to heat from the engine bay. Therefore, the seal and bakelite piston at the back don't get hot and cause the sticking. Also, apparently these aftermarket generic boosters return springs are not as strong.
Since changing back to the booster mounted on the firewall I have had no more pedal return problems.
Also, check for what might contribute to engine bay heat. Retarded timing will give more heat in the engine bay. Extractors??

This is interesting, never heard about this. Thx.

 

[Nate S]

This is interesting, never heard about this. Thx.

Putting in booster #3 today. I guess we’ll just see what it’s fate is. Getting a factory one too from a ‘64 300 that’s being parted out. I’ll rebuild it and eventually put it in for a more factory look.

 

[Ron H]

Putting in booster #3 today. I guess we’ll just see what it’s fate is. Getting a factory one too from a ‘64 300 that’s being parted out. I’ll rebuild it and eventually put it in for a more factory look.

Finished install of new booster this morning with fiddling a lot with the pedal height. It's about an inch higher than I prefer; but livable for now. Part of this hassle is I likely should be on the lower pedal hole but this alignment would require an angled booster bracket I could get - like older GM's had considering my kit is some GM parts. My buddy that's been a great help is convinced that the sinking pedal is because there isn't enough fluid pressure to calipers; but chit, we've bled them 3 or 4 times getting all kinds of steady fluid through them. Part of this I think has been assuring ample travel of the booster rod into the MC thus the pedal height issue. It's about there; but in a perfect sitch could be another maybe 1/4". I'm getting nice braking action. The true 'test' now is to take it for a 20-30 mile drive as this has been when I'd get that sinking pedal going on that a good number of people have thought is a bad booster. I already put in a new MC among other things on the gremlin hunt. I don't know, if this doesn't solve it might end up nuking the booster and go back to manual brakes...

 

[Nate S]

I put the new booster in today. Perfect. Drove it 30ish miles. Hopefully it stays this way.

 

[Ron H]

I put the new booster in today. Perfect. Drove it 30ish miles. Hopefully it stays this way.

Great to hear Nate S! I'm lacking any confidence to drive mine for fear of still no fix. For now I can just make believe it's fixed, as I gawk at it in my garage, over a cold beer...lol. At my age I enjoy (not) spending quality time on my back under the dash...thinking wing-nuts to hold the driver's seat as I've taken it out a dozen times over the past couple years.

 

[Ron H]

I put the new booster in today. Perfect. Drove it 30ish miles. Hopefully it stays this way.

Well - after the new booster in I've driven it pert near 100 miles and gee, feels like I have normal brakes again! Only been some 2 years f-in around with the system. I'd done a load of fixes including a new MC as the old one didn't seem to bleed out in one reservoir after bench and another bleed in the car. New one did fine. The odd sticky pedal I think was the booster not so certain about the pedal sink down; but among the fixes I'm no longer having this so hope to get in some good riding before I have to put it to bed for the winter (though some other projects to do on it while it's sleeping).