1987 Ford F150 V8 Two Wheel Drive Automatic 115000 miles
My brake pedal holds pressure (leaks very slowly) when the truck is in park but loses pressure very quickly when it is in gear. The brakes do hold when I press it firmly to the floor but the pedal is all the way on the floor and ir FEELS LIKE back brakes only (cannot be sure). It has had a slow fluid leak for a couple years but re-filling the master cylinder every 3 months has been the only required fix. Now it stands full of fluid with the same symptoms. I don't see any physical symptoms other than a very small fluid leak between the master cylinder and the power booster. Is there any way to tell for sure which is malfunctioning? Also, if it is the master cylinder, is a junkyard part OK for that or should I give up the $100 for a re-manufactured one at a parts store?
Ok if there are leaks you should replace it as this is a safety issue. If there is now hissing coming from the booster and the vacuum to the booster is good then I would be replacing the master cylinder. I would not do a used one as you may find the same problems or worse. I looked online for pricing and this master cylinder runs from 36 to 52 dollars for a remanufactured on. So check you pricing as a 100 dollars sounds to high.