Intermittent breaking problem

[Derekk]

I have a 2015 Ram, 5.7 Hemi, Big Horn edition.
4 or 5 times over the last couple months I have had my break pedal go to the floor, pump it a couple times and its back to normal. last break pad change was almost a year ago.
this has happened in the morning when its cold and in the afternoon after I have been driving for awhile. No break light or ABS light comes on and there are no codes, the fluid level is just slightly below the max fill line.
I was thinking a bad master cylinder or vacuum booster, but neither of them would be intermittent.

any help or suggestions would be appreciated.

 

[Dean2]

If you break your brake pedal, is it really broken?

In all seriousness, the pedal going all the way to the floor and setting no codes is going to be a bugger to diagnose, like you already know. I would first go look for a vacuum leak, cracked hose etc. It is also possible that the vacuum booster has an issue that only appears intermittently, particularly when the truck is cold. Next time it happens, don't pump the brake pedal. Take a good look around, see if you can spot anything. Try turning the truck off and restarting to see if it still does it. It is at least the beginning steps of figuring it out.

 

[crash68]

Lack of vacuum to the brake booster usually causes a hard pedal. A soft or non-existent pedal is usually fluid related. It could be a leak, calipers issue, bad master cylinder or ABS module issue.

 

[Dean2]

Lack of vacuum to the brake booster usually causes a hard pedal. A soft or non-existent pedal is usually fluid related. It could be a leak, calipers issue, bad master cylinder or ABS module issue.

Very good point on the lack of vacuum.

 

[Derekk]

If you break your brake pedal, is it really broken?

In all seriousness, the pedal going all the way to the floor and setting no codes is going to be a bugger to diagnose, like you already know. I would first go look for a vacuum leak, cracked hose etc. It is also possible that the vacuum booster has an issue that only appears intermittently, particularly when the truck is cold. Next time it happens, don't pump the brake pedal. Take a good look around, see if you can spot anything. Try turning the truck off and restarting to see if it still does it. It is at least the beginning steps of figuring it out.

thanks.
the only thing is, not pumping the break pedal makes it kind of hard to stop

 

[Derekk]

Lack of vacuum to the brake booster usually causes a hard pedal. A soft or non-existent pedal is usually fluid related. It could be a leak, calipers issue, bad master cylinder or ABS module issue.

good point about the lack of Vacuum. can a bad caliper or master cylinder be intermittent?
I don't really know much about the ABS system.

 

[Brian2081]

OK, soft or non existent pedal, fluid is being bypassed. Master cylinder of ABS module.
ABS module will more than likely throw a code, so I would start by looking at the master cylinder. If calipers or lines / hoses have an issue, you would see fluid and never have a good pedal.

 

[indept]

good point about the lack of Vacuum. can a bad caliper or master cylinder be intermittent?
I don't really know much about the ABS system.

For a caliper to do that it would be leaking. For a master cylinder to do that it would be leaking fluid around the piston seals back into the reservoir which you won't be losing fluid. The fact that your fluid is close to max leans toward that.

 

[Derekk]

update on this
I have tested the vacuum booster and master cylinder, both are working properly. I also pulled off all 4 wheels and checked the pads and calipers
pads have about 1/2 life left on them, calipers are working properly. I also topped off the fluid.
now im at a loss as to what to check next

 

[Brian2081]

HMMM, well, I wonder if the ABS unit is doing something funky inside that isn't throwing a code ?