Sjorge3442

My dad has mentioned he continues to have issues with his brake pedal on his 08 STX 4.6L, where after driving on a highway for a bit, he has to pump his brakes about two times in order to have pressure. It seems like the booster is losing its vacuum and needs to be built back up. Once the pressure in the pedal is back, brakes works 100%. I use this truck to tow my double jet ski trailer and I have never had an issue with the brakes.

I recently bled the brakes (he was having this issue before) but he has since gone about 2k miles without issue and now its back. I've inspected the brakes and have found no sign of leakage anywhere, and all pads and calipers appear to be functioning properly.

The only sign of anything I can see, is that around the master cylinder, you can see where a tad bit of fluid has seeped out (we're talking super minimal) and has caused the paint to bubble ever so slightly.

Any tips as to where to start? Truck runs and idles fine and shows no signs of a vacuum leak and holds 22 lbs at idle and doesn't fluctuate. I've read of some people adjusting the push rod between the booster and pedal lever. Any help is appreciated greatly!

nrivera04

I would start with the MC since you can see that it's leaking.

Someone correct me if I'm wrong, but a failing booster would cause a stiff pedal, not one that drops to the floor.

Sjorge3442

Thanks for the reply. Just to note, the touch of paint flak is super minimal. But if its showing, its gotta be seeping right? And yeah, I would think a failing booster would be a stiff pedal, since there's no vacuum to assist in braking.

lutter5-0

Master cylinder is pretty cheap. Throw one at it, see if it sticks?