Oldsmobile, Cutlass, 442, Hurst/Olds, Toronado Parts

Cadillac, Eldorado, Coupe DeVille Parts

Buick 40-60 Series, Skylark, GS Parts

Fusick Automotive Products, Inc

Manufacturer and Supplier of Classic and Antique Automobile Parts

Oldsmobile Parts for 1935 through 1977 88-98-Toronado, Cutlass-442 and Hurst/Olds parts. 

Buick Parts for 1949-60 Full Size Buick Special, Century, Super, and Roadmaster.

Cadillac Parts for 1949-76 Cadillac Sedan Deville, Coupe Deville, and Eldorado

  Licensed by General Motors to produce the Guide Lenses, 442, Oldsmobile, Rocket Symbol, Fisher Body, Body by Fleetwood, for Automobile Enthusiasts worldwide.



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Brake Diagnosis



Brake Diagnosis

Recently we have had  instances where 1953-60 Power Brake units which we had rebuilt for customers were returned to us as faulty.  Upon inspection by our rebuilder the units are checked out and no trouble found on a bench test.  Faulty diagnosis costs time and money.

The brake system on the 1953 to 1960 Buick, Cadillac and Oldsmobile is a simple system but needs proper diagnosis to determine why the car does not stop as it should.  What we see the most is the vacuum system integrity needs to be addressed.  Rubber vacuum hoses need to be replaced, fittings checked, and the reservoir tested.


The following is a condensed version from the Oldsmobile Service Manual in the mid 50's which may help you determine what your problem is:


Brake Diagnosis

The following diagnosis applies to both power brakes and standard brakes unless otherwise specified.

Brake troubles may be easily diagnosed if the complaint is understood. The trouble will always show up in one or more of the four ways listed below. Related parts of the power brake or standard brake system should be checked before dismantling the brakes when a malfunctioning brake system is encountered. 

Hard pedal feel may be caused by:

A. Power Brake vacuum failure due to:

a. Faulty vacuum check valve.

b. Collapsed vacuum hose or fittings

c. Plugged or loose vacuum hose or fittings

d. Leaking vacuum reservoir tank.

        B. Bound up pedal mechanism

        C. Glazed linings

        D. Grease on brake drums or linings

        E. Power brake unit trouble due to:

            a. Internal vacuum hose loose or restricted.

            b. Vacuum leak in vacuum piston assembly or past leather piston packing

            c. Leak at power cylinder to master cylinder mounting face (Bendix)

            d. Faulty vacuum seal (Moraine)

            e. Restricted air cleaner

            f. Jammed push rod plunger (Bendix)

            g. Jammed air valve (Moraine)

            h. Broken counter-reaction spring (Bendix)

            i. Leak past atmosphere poppet (Bendix)

            j. Leak past floating control valve (Moraine)

2. Grabby or severe brakes caused by:

        A. Grease or brake fluid on linings

        B. Scored drums

        C. Anchor pins improperly adjusted (new linings)

        D. Power brake unit trouble due to:

            a. Vacuum leakage in reaction diaphragm

            b. Sticking push rod plunger or air valve

            c. Faulty pivot arm and vacuum poppet action (Bendix)

            d. Restricted diaphragm passage

            e. Master cylinder plunger binding in vacuum piston guide (Moraine)

    3. Pedal goes to floor (or almost to floor) caused by:

        A. Brakes require adjustment

        B. Air in hydraulic system

        C. Hydraulic leak in lines or at wheel cylinders

        D. Fluid reservoir needs replenishing

        E. Cracked drums.

        F. Power Brake leakage at:

    A. Compensating valve or seal

    B. Hydraulic plunger seals

    C. Outlet fitting

    D. Sand hole or crack in master cylinder

Brakes fail to release (or slow to release) due to:

A. Bound up brake pedal linkage

B. Weak brake shoe return spring or rusty bosses on backing plate

C. Power brake unit troubles due to:

a. Faulty residual check valve

b. Excessive hydraulic plunger seal friction

c. Faulty compensating valve (Bendix)

d. Excessive piston packing friction

e. Restricted air passage in vacuum piston

f. Restricted air cleaner

g. Sticky push rod plunger (Bendix)

h. Sticky air valve (Moraine)

i. Broken piston return spring

j. Broken air valve return spring

k. Broken push rod plunger return spring (Bendix)