Brakes are extra sensitive - Impala Tech
Brakes & Suspension Conversion Questions & more

 
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post #1 of 5 (permalink) Old 06-24-2020, 05:59 PM Thread Starter
Ben
 
 
Join Date: Jun 2020
Posts: 6
 
Brakes are extra sensitive

I have a 68 impala convertible. Stock factory power drum brake car. My car sat many years before mechanical restoration. My question is has anyone come across power brakes that are super sensitive. You barely touch the brake pedal and all wheels lock up. If you drive the car carefully no problem but apply brakes quickly and it results in four wheel lock up. Keep in mind everything is new or rebuilt. New lines master booster wheel cylinders shoes hardware etc. Any advice as to what to check is appreciated.
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post #2 of 5 (permalink) Old 06-24-2020, 08:57 PM
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Drum brakes are self activating. that is a way of saying you have to pull the shoes away from the drums because they want to grab as consequence of their design. That is why the springs that retract the shoes are so strong.

The design is such that the leading edge digs in and drags the rest of the shoe along for the ride until the wheel locks. If the installation didn't mount the shoes correctly (there is a leading and trailing shoe) it could aggravate the issue. If any oil or grease gets on the shoes they swell and grab.

I would take the car to a brake mechanic such as Brake-o to see if there is a physical reason for your brakes grabbing.

Big Dave
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post #3 of 5 (permalink) Old 06-25-2020, 06:18 PM Thread Starter
Ben
 
 
Join Date: Jun 2020
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Thanks for the advice. I have done all work by myself so I will pull the drums and see if I possibly reversed the shoes. Great tip I never thought about brake shoe placement.
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post #4 of 5 (permalink) Old 06-26-2020, 01:48 AM
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The longer lining shoe was placed on the rear of the axle on the vehicle and shorter lining shoe faced the front. The front shoe is the self-energizing shoe and was called the primary shoe (rear shoe is refered to as the secondary).

Springs are all color coded and described in a Chiltons or a Motors manual. I would say they can only go on one way but every time I say that some one would drive in with the springs missing or attached to the wrong part.

Big Dave
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post #5 of 5 (permalink) Old 06-26-2020, 06:23 PM Thread Starter
Ben
 
 
Join Date: Jun 2020
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Hello Dave you are correct just finished a test drive after correcting front brake shoe placement. Fronts were reversed rears were fine. Stops as it should. Years ago I was taught to leave one side of drum brakes untouched while working on other side to be used as reference while assembling. This did not happen due to painting restoring parts prior to reassembly . Thanks again for your advice.
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