I have a 2001 Ambulance chassis/diesel. Tonight on the way home my brakes went out. Managed to drive it home and still had some pedal but not much. I don't see any busted/leaking lines and also this only has 40,000 miles on it, it's not all rusty and corroding from the salt here in NY. I am thinking it is a bad master cylinder or the brake booster, any thoughts guys ?

It did not all of a sudden go to the floor like a busted line. As I attempted to stop to make a right turn the brake just faded away and the pedal went to the floor, if I pumped them it would build a little pressure but quickly fade. One last thing I have never been impressed with the brakes on this thing, they have always been there but never very impressive.
Thx Dave

 

Hows the fluid, and did you look at calipers for leaks ? That low of miles, have you serviced the caliper slides ?

 

Check that fluid level in the master cylinder. If it isn't low then the master went bad. If it s getting low then probably a busted cylinder in the rear drum. Top off the reservoir if low and then check in the morning for the leak.

 

Since it's a diesel, it has a vacuum pump. We have an 03 4x4 "box" van here at work and the brakes went out and it was the vacuum pump. And yes the brakes absolutely suck on ours, also.

 

Check your vacuum pump and connections at the vacuum manifold (near the brake booster). If those check out, then the problem is the brake booster.

 

Since I have a Diesel ...when the Vacuum pump fails the pedal is HARD like old school brakes.... and it still does not stop.... it is a Master Issue ( Could be a line too ) ...If it does stop it is a Booster Issue....I beleive you have rear Disc Brakes ...It should be a Dana 70 HD with a 4:10 FF so it should be Disc...SO you do not have rear Drums...so No cylinders...

 

My guess is master cylinder, had a similar experience.