Well yesterday I was leaving the school parking lot and noticed that my brake pedal was hard as a rock after I had started leaving the lot. I almost rolled into someone because the breaks were so damn weak. The pedal got softer and went back to normal after I got up to like 35 mph. It didn't do it again that day. When I started her up this morning and was about to turn around in the driveway, it did the same thing and just kept rolling despite me trying to mash the immovable brake pedal. The pedal went back to normal as soon as I got on the road.

What the hell isngoing on with my brakes??
Thanks for any help!

 

Might be the power brake booster going out. Check the vacuum line going to the booster for any cracks. If the line is ok then I would imagine the booster is losing air internally. If it the pedal feels normal when you drive/engine running then I bet that booster isn't holding vacuum.

 

This is interesting because I'm having the same thing happening to me on my 56 with a new booster on it...

 

It sounds like a bad check valve in your vacuum booster. This can cause excessive pressure in your master cylinder, making it difficult to press the brake pedal.

I'd change the booster.

 

Even a new booster won't work without a consistent vacuum source.

 

I have lots of vacuum..

 

Good point in checking the vacuum line first, easy and cheap to replace. Boosters are expensive, so hopefully that's all it is.

 

Just to add to what I've noticed... the brake light comes on at stops and while rolling at very low speeds. When this happens the brakes barely work

 

sounds like your vacuum pump is dead. the diesel has a belt driven vacuum pump to supple vacuum for the power brakes because the diesel engine does not make vacuum like a gas engine does.

 

Well I ordered a vacuum pump last night but today half way on the way to school the brake light came on while cruising at 70.. something that never happened before... and the pedal is hard 24/7. Truck is very hard to stop because of this.