I have a 56 olds 88 and power brakes work great when I first start it up but when I get it on the road after a few light braking events I feel my pedal getting weaker and thus brakes get weaker till one time the pedal just went to the floor and would not stop the car at all...kinda scary!!!!....Annnyyyway just wonder if anyone has experienced this and what was the fix....I have check brake fluid level and its 1/2" up the stick so I assume goos but there is no line on dipstick...Also I have no leaks at any brake cylinder or line....I also removed the vacuum check valve and the thru line is not clogged but the tee part that goes to the carb seem to be a little obstructed and the check valve part not working at all....Any help would be greatly appreciated....I was going to just pull unit and get it refurbed but it works just fine on startup and for a while and that tells me it might be the power unit is working and doesn't need a rebuild!!!

 

Sounds like a bad master cylinder if there aren't any other leaks.

 

Let me ask my question differently...Would ANY KIND of vacuum problem cause brakes to fail and go straight to the flloor or just get super hard to push to stop vehicle????

 

ANY??? Probably not... anything is possible.
A vacuum leak to the power assist would make the pedal firm. A hydraulic leak such as an internal leak in the master would make the pedal fade intermittently. An external hydraulic leak would make the pedal fade consistently.

 

Post some pics of what you are looking at and checking. Never heard of a brake reservoir having a dipstick. Are you checking the power steering unit and not the brake fluid? If that's the case you just might be out of brake fluid.

 

The master cylinder is under the floor and has a dipstick near the firewall below the steering column. It is attached to the bottom side of the filler cap. If you don't know where it is, why question the OP. The thing is a PIA to check and a bigger PIA to fill.

 

Apologies, I didn't realize that was how this model was built. Learned something new today, thanks.

 

And even worse if you have a mid fifties with factory AC.(I know) You have to remove the tire and open an access panel in the wheel well to get at the master cylinder. (Just thought I'd mention this to let everyone know that I'm still here!)

 

Glad you are still here Frank. Good hearing from you with some good advice. You would know about the factory air conditioned car for sure.

 

While you on the brake service how old are the rubber lines from the frame to the wheel cylinders?
Ill bet the system needs to be bleed. That must be fun with that set up!
You get about 3-5 years of life on brake fluid before it starts breaking(ha) down.

 

rubber lines are at least 10 years old....I have zero leaks on entire brake system tho!!!!

.My plan was to have brakes gone thru after they failed and I almost crashed....BUT nobody wants to touch these old car anymore....I am older and live in Oakland County Michigan and even tho these cars are all built here I can't find anyone to work on these 50's cars....However f I remove entire Power Brake unit and send it to them they will fix it for $600 which is what I guess I will have to do!!!!????

 

Used Karps in California for a '56 Tbird brake parts and was quite satisfied with their service, I'd go to them again if/when needed.

 

X2. Karps is the best bar none.

 

Thanks sugar bear and remoldsman...Karps in CA was actually who I was going to send it to....Now just got to get motivated to taking the beast out thru the inside of the car!!!!

 

Update.....I believe my brake unit is a Delco Moraine because my dipstick handle is a solid metal blade and not a wire handle....The top of my dipstick neck is way above the reservoir lid so I guess I will just measure that distance to figure if my fluid level is at the top of lid or not....I did read something somewhere that said level on stick should be just at end of stick and mine is 1/2" above that so I may be overfull!!!???....I do have a check valve in vacuum line and I removed it and blew and sucked threw it and it doesn't seem to be working at all....matter of fact it seems moderately restricted in the path to the carb....BUT tubing to vac check valve is dry as a bone so no brake fluid is backing up that way.....ANNNYWAY....ANY HELP ANYBODY can give me diagnosing this would be appreciated.....Like I said before....Brakes work great on startup and then brakes get weaker and weaker and fade to nothing (pedal to the floor) after a few road stopping events....I guess my thinking is if seal between vacuum booster and master cylinder has failed then how is it resetting itself after I turn car off???....

 

Do you still have the vacuum tank on your car?

 

yes still have tank but haven't checked it since its buried in fender....when I disconnected the vacuum check valve I blew on line that goes to tank and didn't hear any leaks....also when I disconnected hose to tank I expected a sucking noise but none!!!

 

do you know what would happen if I drive car with the vacuum line disconnected to power brakes?

 

The vacuum tank is really there for an emergency in the event you lose engine power. It stores enough vacuum to allow you to stop the car. You could bypass it and see how the brakes do. If they work okay, then you have a leak in the tank. After this many years, it is very possible you have a leak from condensation rusting the inside of the tank. On the 54 I had, the tank was inside the frame on the left side. In 56 they probably moved it since 56 was the first year dual exhaust were available. I had one make for my 54 which was simply a piece of 3" tubing with some ends put in it. I hope all this makes sense.

 

If I hook carb vacuum hose directly to brake unit vacuum input do I run the risk of getting brake fluid in carb???...Also, if I disconnect all vacuum lines from brake unit, cannister and carb I adsolutley need to plug both the carb port and brake unit correct???