1975 Eldorado Loss of brake pedal?!

[AustinEldo75]

Pulled down my steep driveway on Sunday to find a very soft pedal.  The “brake” indicator light comes on with the pedal almost fully pressed.   

The car hasn’t shown any braking issues before, and it drive beautifully on Saturday (day before issue)

I can’t see that I’ve lost any fluid.  master cylinder seems full. 

Where should I start?

Thanks
Danny G

[STS05lg]

Danny,

Sounds like the Power Brake Booster has given out. The system has a boost reserve. If you use the brakes after the engine is shut off or the Power Brake Booster has failed, the brakes will have pressure but only enough to use the brakes one or two times. After the reserve is used up the pedal will get really soft. Therefore, it appears you have lost be pressure from your Power Brake Booster. I assume you have checked the master to make sure there is fluid in the primary and secondary. If the secondary is low on fluid the pedal will get soft also. Hope this helps.

Lynn

[hornetball]

My experience is that a failed booster leads to a hard pedal . . . like a REALLY hard pedal.

If there is really no leak, this sounds like the pistons were recessed into the calipers ("pad kickback" in racing lingo).  A bad wheel bearing or anything else that makes the discs not run true causes this.

Tie breaker would be whether the brakes get firm with pumping?  If you have a leak, they don't.

[bcroe]

Pulled down my steep driveway on Sunday to find a very soft pedal.  The “brake” indicator light comes on with the pedal almost fully pressed.   

The car hasn’t shown any braking issues before, and it drive beautifully on Saturday (day before issue)

I can’t see that I’ve lost any fluid.  master cylinder seems full. 
Where should I start?   Thanks  Danny G 

I would get the wheels off and look for any brake fluid there or along
the lines.  Keep an eye on loss at the master cylinder.  Bruce Roe

[Cape Cod Fleetwood]

Happened to The Ark last spring. Michael said to run my hand inside the rims, I'll find which wheel is leaking, right rear!

\m/
Laurie

[TJ Hopland]

I too don't think its the booster.     Is the fluid in the master cylinder level fine and stable?   Or was it low and you just don't (yet) see any leaks under the car?      If there is truly no fluid leak or level issue then its likely an internal issue inside the master cylinder.   Wear and or corrosion in the bore so fluid is just bypassing around the piston.   Happened to my 73 a couple years ago.

Story time you can skip if you are just looking for a fix.....

On mine I glanced under the car and could see the whole back of one of the front wheels was wet.   Figured its been like 15 years since I did anything other than bleed the brakes so it was likely a failed hose.   Ordered parts and got it set up in the garage to work on it and got a better look at things and discovered it was the CV boot that let go and made the huge mess of grease all over.   Brake hose still intact and it was the MC that failed.   Based on age and the mess I ended up with all new hoses along with the new MC and some new pads.   Old pads were still 2/3 material but had got grease on them from the CV.   

[hornetball]

BTW, sometimes a MC will leak through the main bore into the booster.  In this case, you will notice the fluid level dropping, but everything will be dry near the wheels.

[AustinEldo75]

I'm going to install a MC tomorrow, to see if that resolves the problem.  If not I think I'll send both the booster and MC to White Post Resto for complete rebuild. 

There are no options available for Boosters on the Market.  Several Manufacturers, but all are out of stock indefinitely...

Thanks gents I'll keep you posted

D. Gomez
AustinEldo75

[Jeff Rosansky CLC #28373]

They can leak slowly. On the 70 the fluid was just about gone one day. No signs at all and really no signs of leaks outside the wheels. Found it when I pulled the drums. It must have been oozing slowly for a while until it finally got to where it didn't work any longer.
Jeff

[cadillacmike68]

BTW, sometimes a MC will leak through the main bore into the booster.  In this case, you will notice the fluid level dropping, but everything will be dry near the wheels.

This is correct. If you can't find a leak along the lines, your MC has bought the farm and took the booster out with it.

[cadillacmike68]

I'm going to install a MC tomorrow, to see if that resolves the problem.  If not I think I'll send both the booster and MC to White Post Resto for complete rebuild. 

There are no options available for Boosters on the Market.  Several Manufacturers, but all are out of stock indefinitely...

Thanks gents I'll keep you posted

D. Gomez
AustinEldo75

You are going to need a booster as well. They are out there. If I can find one for a 1968, you should be able to get one for a 1975.