Hi everyone. I have a problem and I haven't been able to find a solution.

When driving, sometimes I will notice that my brake pedal feels slightly sunk in. Not all the way. Maybe half an inch or so. When I press the clutch pedal, the brake pedal becomes fully depressed.

Here's a video of this happening while my engine is shut off and I'm parked:
Now I will let you in on some background. I had my slave cylinder and clutch replaced about 3 months ago. It was a DIY project, mostly done by my brother who has more auto knowledge than me. At one point the weather sucked, and my truck sat for awhile with the transmission and the stick shift removed. I mention this because at a later time I noticed that there was a significant amount of moisture on the area surrounding my pedals. I do know that there was some rust in that area, and we were able to loosen the clutch quite a bit by spraying a lot of WD-40.

My guess is that it is one of 3 things:
- There is rust on the pole / connector that connects to the pedals, and it's causing some sort of snag to occur. The snag is broken when the clutch is pressed, allowing the brake pedal to free itself.
- There is an issue with the master cylinder.
- There is an issue with the power brake booster.

Most people that I've mentioned this issue to, but who haven't seen the video, suggest it is either the master cylinder or power brake booster. However, no video I've seen online seems to accurately depict my issue. And my brakes don't feel particularly hard to activate.

Before I embark on a mission that takes me in the wrong direction, could anyone provide some additional insight?

I appreciate the time and effort. Thanks!

 

Google: ford ranger clutch brake assembly

Just to see what it looks like up above, yes could be rod bushings are bad causing pedal to not return.

Wouldn't be master.

Booster has the pedal return spring inside.

How power assisted brakes work:
Inside the booster is a diaphragm, most of the booster space is used for low pressure storage(vacuum), so diaphragm is very close to firewall side of booster.
A large pedal return spring is in the low pressure area.

When engine is running at idle it will have approx. -20" of vacuum, that is transferred to booster via a check valve, so lower pressure isn't lost while accelerating(vacuum drops to -2") or if engine should stall.

How this assists driver, air pressure at sea level is 15psi, when you press on the brake pedal the push rod is opening the Atmosphere valve, this lets in the higher pressure to the backside of the diaphragm, this pressure difference 'assists' the driver in pushing on the Master cylinder.
When you take your foot off the brake pedal the push rod/pedal should come back up, closing the atmosphere valve.
If atmosphere valve is staying slightly open then pedal can't return fully, the pressure difference is keeping pedal down.

Shut off engine.
You should get 2 or 3 "assisted" brake pedal pushed before pedal gets hard, low pressure has been used up.
Now see if pedal still sticks down that 1/2", if it does I would guess clutch brake assembly myself