Mechanics

4 WHEEL DRUM BRAKES NOT WORKING

1969 Oldsmobile Cutlass

Brakes problem
1969 Oldsmobile Cutlass V8 Two Wheel Drive Automatic 72,660 miles

MY 1969 CUTLASS HAS DRUM BRAKES ALL THE WAY AROUND AND WOULD PULL TO THE LEFT LIKE YOU WERE TURNING LEFT WHEN THE BRAKES WERE APPLIED. I HAVE REPLACED THE MASTER CYLINDER, DISTRIBUTION BLOCK UP FRONT AND IN REAR, ALL BRAKE LINES, BRAKE SHOES, ALL HARDWARE AND SPRINGS, WHEEL CYLINDERS, TURNED THE DRUMS AND BLED THE ENTIRE SYSTEM 4 TIMES AND HAVE ABSOLUTELY NO STOPPING POWER AT ALL. AM I MISSING SOMETHING SOMEWHERE CAUSE I JUST DON'T KNOW WHAT ELSE TO DO.
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Frank6696
September 22, 2010.



Hi frank6696. Welcome to the forum. Elaborate on " no stopping power". If you mean the brake pedal can be pushed all the way to the floor when you're sitting in the garage, that is typical but only on GM products. That would equate to the wheels locked up when driving on the road. In other words, the pedal characteristics on a GM car can be misleading if you don't just go out and drive it.

If the pedal goes to the floor with little or no resistance, there is air in the lines yet or the clearance between the shoes and drums is too large. One trick is to watch for air bubbles in the master cylinder reservoir while a helper pushes the pistons back into the wheel cylinders. Doing so will force brake fluid back up there along with some of the trapped air. Seeing any bubbles is proof air is still the problem.

Another trick to check for excessive shoe clearance is to place c-clamps over the wheel cylinders so the pistons can't move out. If the pedal becomes firm, remove one clamp at a time and assemble that brake. When you find one that causes the low pedal, look for the star-wheel adjuster set properly and in its correct location.

If the pedal is firm but the brakes don't stop the car well, check for wheel cylinders that are too small in diameter, particularly the front ones. Glazed linings will do that too but since you machined the drums, the rough surface would have cleaned off any glazing on the linings.

If the diameter of the wheel cylinders or the bore in the master cylinder has been changed, it will affect pedal travel.

As a last resort, you can disconnect steel lines from the combination valve and install plugs temporarily to see if the pedal becomes firm. That will help identify which hydraulic circuit has the problem.

If the only problem is the brake pull, watch each wheel cylinder while a helper slowly presses the pedal no more than about half way to the floor. If the pistons don't move in one cylinder or the pistons don't move back under return spring pressure, suspect a constricted rubber hose to that wheel. This is more common on hoses that have an anchor bracket crimped around the center. Rust builds up and pinches off the hose. That will result in only one brake applying under light to normal pedal pressure.

Keep in mind that since the drums were machined, they will be different diameters and until the shoes have worn in, the area of lining contact with the drums will be different from side-to-side. That is a common source of brake pull during the break-in period, particularly if there wasn't a problem before the work was done. If there was a brake pull previously, inspect the upper and lower ball joints and upper and lower control arm bushings for free play or excessive movement that allows the spindle to change position relative to the steering linkage. A clue to the source of a brake pull is to observe if the steering wheel shifts position during braking. If it does, suspect a brake problem. If the steering wheel stays straight but the cars pulls to one side when braking, suspect worn steering or suspension components.

Caradiodoc

Caradiodoc
Sep 22, 2010.
The brake pedal is stiff just as if everything was working properly but it will not stop car when moving, not even slow it down. When it was working and you applied the brakes the steering wheel would jerk to the left. The last time I drove the car, it stopped at the stop light bt then it wouldn't stop when trying to slow down to turn into gas station.I then triied to get cr home which was 2 miles away and had to run a red light crossing a busy highway and when turning into subdivision which is instantly downhill when turning in made for an interesting ride and I finally got it stopped 10 feet from going right through someones house. I guess i'll try adjusting shoes out as far as possible and give it another try. Thanks for your help.

Tiny
Frank6696
Sep 22, 2010.
Is it possible there is a power booster that isn't working? If there is one on your car, hold steady pressure on the pedal then start the engine. You should feel the pedal sink down when the manifold vacuum shows up. When you stop the engine, after waiting for up to a minute or more, you should still have two or three power assisted pedal applications from the vacuum stored in the booster. If the power assist goes away right away, the check valve is defective.

A lot of cars with drum brakes didn't use power boosters. The next thing would be to remove one drum at a time and watch to see if both pistons move when a helper presses the pedal. Check too that the shoes are installed correctly. The shoe with the shorter lining goes toward the front of the car. Its job is to grab the drum and try to rotate with it. That action causes it to apply the rear shoe with the longer lining. It's his job to actually do the stopping when driving forward.

It is extremely important to not get any axle grease from the wheel bearings on the linings or drums. It's even a good idea to wash fingerprint grease off before the final assembly. Once the linings get hot, any grease will soak in and can no longer be removed. That contamination will cause squealing on disc brakes, but on drum brakes, it can cause grabbing, chattering, or glazed linings that have very little friction.

If your pedal feels stiff like normal, suspect glazed linings, the shoes are installed backwards, or two short linings are on the same wheel. If by " stiff" you mean the pedal has less travel than normal or is harder than normal, look for a blocked fluid path to one wheel. I can think of a few things but you replaced them already.

Caradiodoc

Caradiodoc
Sep 23, 2010.
WELL I PUT A 3RD MASTER CYLINDER ON IT, MAKING SURE TO PROPERLY BLEED IT BEFORE INSTALLING IT. I THEN WENT AROUND AND REMOVED ALL THE TIRES AND ADJUSTED THE BRAKES OUT AS FAR AS I COULD WITHOUT LOCKING UP THE DRUM. THEN I WENT AROUND AND BLED ALL THE BRAKES. THE CAR IS FINALLY STARTING TO STOP, NO WHERE NEAR HOW THEY SHOULD BE BUT IT'S A START. ALTHOUGH THEY GRIND AND SOUND LIKE THEY ARE FALLING APART WHEN TRYING TO STOP WHILE IN REVERSE GOING BACKWARDS AND IT TAKES ALL THE PEDAL TO STOP WHEN GOING EITHER WAY, BUT IT'S GETTING THERE. YOU'VE HELPED ME GET IT THIS FAR NOW I THINK IT'S JUST FINE TUNING EVERYTHING. I'VE ONLY HAD THE CAR FOR 3 MONTHS SO IT'S HARD TO JUDGE NOT KNOWING HOW THE CARS BRAKING ABILITY WAS ON A NORMAL BASIS SINCE THEY WERE MESSED UP WHEN I GOT IT. HERE'S A PIC OF THE CAR


http://www.2carpros.com/forum/automotive_pictures/575850_Picture_141_1.jpg



http://www.2carpros.com/forum/automotive_pictures/575850_Picture_145_1.jpg


Tiny
Frank6696
Sep 23, 2010.
Oooohh! I like red!

It still sounds like there is something significant that has been overlooked. It shouldn't be that hard to get brakes to stop the car. I forgot to mention also that duo-servo drum brakes are self-energizing so they commonly don't require a power booster. While boosters were around for a long time, their use was needed more when disc brakes came around in the late '60s.

Duo-servo brakes just means the front shoe grabs the drum and rotates a little with it. That movement pushes the bottom of the rear shoe into the drum. The second action is the other piston in the wheel cylinder pushing on the top of the rear shoe.

Regardless of the type of brakes, they should be strong enough to lock up the wheels and hold the car from moving while trying to accelerate away from a stop.

Caradiodoc

Caradiodoc
Sep 24, 2010.