my 51 gmc 720 has a double diaphragm booster on it which im not so sure that its working properly and dont know how to tell if it is or only partially working. the info on it says "midland 300308"

yesterday when i started the truck i had my foot on the brake pedal. when it started the pedal moved slightly to the floor which tells me something is happening with it. when i was driving it to a garage down the street from where its parked to pull the wheels and inspect the brake system parts and it didnt seem to be working.i had no strong braking action or any power assist to do any braking even with a full hard pedal it was like there was no response from the brakes at all except for a slight drag.

i did notice while in reverse i had srong brakes?? if i this much brake going foward i wouldnt be posting this.

i know this is not the original booster. i can see the marks on the frame where it was mounted previously.

how do singe and double diaphragm differ in operation? :confused:

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