1968 Chrysler 300 power brake problem

[bronze turbine]

Every once in a while when you press the brake pedal, it feels like there's no power assist, like the engine isn't running. You can still stop the car but have to push a lot harder. Doesn't do it every time. What can cause this?
Thanks.

 

[CBODY67]

Might be something internal to the booster which triggers the vacuum assist? Is the vac source to the booster intact and fully functional? If the disphram in the booster was bad, the engine would miss every time the brake pedal is depressed and probably HISSSSS, then everything returns to normal when the pedal is released and returns upward.

From my experiences. Others might have different experiences.
CBODY67

 

[Davea Lux]

Check the vacuum hose to the booster. The internal lining sometimes separates and blocks the hose. This will usually be an intermittent condition like what you are describing. If the hose is the OEM unit it is now over 50 years old and should be replaced as a preventative measure in any case. Be sure to use vacuum hose not fuel line or hydraulic line because the construction on vacuum hose is different. A bad booster will usually hiss if the diaphragm is bad.

Dave

 

[1970FuryConv]

Check valve: I started having problems when a crack developed between the grommet area of the check valve and the body of the check valve. I discovered it when I went to remove the check valve and the grommet portion stayed in the grommet.

 

[Gerald Morris]

Might be something internal to the booster which triggers the vacuum assist? Is the vac source to the booster intact and fully functional? If the disphram in the booster was bad, the engine would miss every time the brake pedal is depressed and probably HISSSSS, then everything returns to normal when the pedal is released and returns upward.

From my experiences. Others might have different experiences.
CBODY67

That's EXACTLY what the booster on Gertrude has been doing, and when the "hiss" got bad enough to attenuate power braking last week, I pulled the booster. I now will pull the manual plate and pedal off Mathilda, install THAT on Gertrude, and bid brake booster issues "Good riddance" on that car! I tried driving the MC with the pedal and plate meant for the booster, but, sure enough, the moment arm from the pedal pivot to the piston rod needs to be SHORT for manual brakes to get enough force from the length of the brake pedal. Consequently, driving at the moment is just like driving a power brake system with a dead booster.

Folks who consider future manual brake conversions need to keep this stuff in mind. Likewise, the pedal brackets differ a bit, so its best just to take the plate, bracket and pedal all.

Pity rebuilt boosters have become nearly unobtainium, aside from Cardon't. I like "rebuilds" more rigorous than merely cleaning the outside of an item. Reckon I'm just an evil old fascist, eh?

 

[Davea Lux]

That's EXACTLY what the booster on Gertrude has been doing, and when the "hiss" got bad enough to attenuate power braking last week, I pulled the booster. I now will pull the manual plate and pedal off Mathilda, install THAT on Gertrude, and bid brake booster issues "Good riddance" on that car! I tried driving the MC with the pedal and plate meant for the booster, but, sure enough, the moment arm from the pedal pivot to the piston rod needs to be SHORT for manual brakes to get enough force from the length of the brake pedal. Consequently, driving at the moment is just like driving a power brake system with a dead booster.

Folks who consider future manual brake conversions need to keep this stuff in mind. Likewise, the pedal brackets differ a bit, so its best just to take the plate, bracket and pedal all.

Pity rebuilt boosters have become nearly unobtainium, aside from Cardon't. I like "rebuilds" more rigorous than merely cleaning the outside of an item. Reckon I'm just an evil old fascist, eh?

Not all rebuilt boosters are a piece of crap. Booster Dewey does a good job on them.


www.boosterdeweyexchange.com

Dave

 

[Gerald Morris]

Not all rebuilt boosters are a piece of crap. Booster Dewey does a good job on them.


www.boosterdeweyexchange.com

Dave

I'll take your advice to heart! You've been A-1 Right On about everything else in this matter, so I'll look at Dewey's shop, see what the turn-around time is, and go from there. Regardless, I need working brakes NOW, so I'm fixing to crawl under the steering wheels again. I can do this easily enough, but will SUFFER for the following 2 days. That's OK, its going to RAIN the rest of the week. I'll take dope to cope, AFTER the job.

Semper Gratias!