Ok guys here is a tough one. I am losing pressure on the pedal in reverse only and only half of the time. I will go to back into a spot and the pedal goes to the floor. I pump it and it gets pressure back. Obviously this is dangerous as hell and scares me when it happens. Front brakes are new with new calipers and rotors/pads and were bled properly. I have thousands of miles on them without any problem and then this starts happening.

There is not much info out there about this but I am thinking maybe master cylinder? Anybody who knows brakes please chime in and let me know what you think. It's a 2005 dakota SLT RWD 4.7 front disc rear drums.

Thanks

 

I'd agree on the master cylinder also. I had a similar problem years ago, after throwing a good bit of money at it by changing practically all my brake components i was still having an intermittent loss of pedal. I ended up changing the hoses and that solved it. Of course that was back when I lived in AZ, guess that desert heat got to it.

 

Yeah it was like 119 yesterday. I will call my mechanic and see about having him swap the master cylinder. Thanks.

 

+1 master cylinder. Especially if you are not loosing fluid anywhere. The only strange part is that it only happens when you reverse. It's not like the Dakota changes the bias of the brakes when going forward or reverse. Mechanically, the master cylinder and the rest of the braking system function exactly the same regardless of how you go. Could just be a fluke that it only happened when you were reversing and could have happened at any time.

 

I'm leaning toward something related to the rear drums since it only occurs in reverse. All the other parts don't know and don't care which direction you are headed. The drums are the only brake part that behave a little different when going from forward to reverse.

By design, the rear drums are supposed to automatically adjust when in reverse. Seems possible that an adjuster broke, anchor spring came off or something else that is letting the shoes shift and increase their distance to the drum when in reverse. All it takes is a few thousandths extra clearance and that pedal sinks to the floor to make up for that extra clearance between the shoe and the drum surface.

 

So they went to the floor going forward yesterday on a highway offramp so I took it straight to my guy. He is changing the master cylinder and said the fluid was contaminated. I only bled it when I changed the calipers so I probably should have flushed and started fresh. Lesson learned. I hate working on my truck in the 100 plus degree heat so I probably did it to save time. Thanks everyone I will update once the work is complete today.