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Brake problem on 47

Started by cadillac60, May 25, 2015, 09:24:44 AM

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cadillac60

 A New brake system was installed 2,000 miles before I purchased the car.  I noticed when test driving it the pedal seemed lower than normal. The system was filled with dot 5 silicone fluid.  The problem I am experiencing is if the the car sits for a few days and I push on the brake pedal it almost goes to the floor. Once I pump it a couple of times the brake pedal becomes hard. I have adjusted the brakes to make sure it wasn't out of adjustment & all is OK with the adjustment. Any help on this problem solving would be appreciated.

Bruce Watson
Bruce Watson

Bobby B

#1
Bruce,
  Hi. Single master cylinder. If there's no visible external signs of leakage, then it's most likely  full of air or leaking past the cup seal in the master. Bleed it first. Did you bench bleed the master before you installed it? This step would've saved a little bit of aggravation when bleeding. I hope the complete system is brand new if you're using Dot 5 silicone, as it is not compatible with glycol based fluids ( Dot 3,4, and 5.1). Are you sure it's not Dot 5.1 which is glycol based and compatible? The only advantage to silicone fluid is it's higher boiling point, and it's less prone to absorb moisture. Its compressibility when warm is its weakness, along with its tendency to soften all the rubber seals in your system. Race cars and Motorcycles use Dot 5, along with people who have $$$$ paint jobs and are afraid of spilling it on the car. Hope this helps.
                                                                                                               Bobby
1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

cadillac60

Bobby,

Thanks for the reply, as mentioned the brakes were done before I purchased the car so no I didn't bench bleed the M/C.   The brake fluid used was Prestone Silicone Dot 5.

Bruce W
Bruce Watson

m-mman

Yeah good idea.
Start with a good PRESSURE bleed where somebody pushes the pedal while somebody else opens the bleeder screws.

The use of 'one man' vacuum bleeders dont always get ALL the air out. (what might have been done when the brakes were repaired earlier)
1929 341B Town Sedan
1971 Miller-Meteor Lifeliner ambulance
Other non-Cadillac cars
Near Los Angeles, California

CLC #29634