What should the brake pedal feel like?

[Ned81]

1998 m1078
I dont have much experience with air brakes. The truck seems to stop ok but I am able to push the pedal to the floor if I push hard enough. Is that normal?
Thanks!


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[Suprman]

It should be pretty firm with air in the system. No air sometimes they do feel a bit different. Brand new pedals do feel very firm though

 

[Ned81]

It feels “normal” when regular stopping but jamming the brakes feels no more firm. And I can push it to the floor. I know it a lot of weight so it doesn’t stop like a car but going to the floor seems odd.
No air leaking when using the brakes.


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[Suprman]

Lmtv braking is not like the older m939 air brakes. They are pretty responsive and stop well.

 

[Wingnut13]

The dad part of me just can’t resist saying it feels like metal with a bit of rubber on the top of it. But I generally just use my booted foot….. and it doesn’t feel much.

I’ll just show myself out now….

 

[tennmogger]

Pedal should not go to the floor.

 

[Ned81]

The dad part of me just can’t resist saying it feels like metal with a bit of rubber on the top of it. But I generally just use my booted foot….. and it doesn’t feel much.

I’ll just show myself out now….

I kinda asked for it. Lol


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[Ned81]

Where should I begin trouble shooting the pedal going to the floor?


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[Suprman]

It probably needs a rebuild

 

[tennmogger]

Your description includes some challenges. First, no air leaks, yet the pedal goes to the floor. That should mean that full system air pressure has been proportionally applied to the braking system in both front and rear circuits as you increased foot pedal pressure. Yet you describe no increase in pressure to push the pedal to the floor. What is the air pressure showing on both the dash gauges? What does the gauge pressure do as you hold down the pedal?

To get the 'to floor' symptom either system pressure going into the treadle valve is low, or there is a leak beyond the treadle. A leak at the treadle is going to be noticable. It is right next to you. A leak, or leaks at the brakes could be masked by engine noise. Have you had someone listen while the pedal is pressed? A leaky diaphragm in each circuit would give your symptoms. Or a leaky shuttle valve in front or rear circuits, or a combination.

I do not think you have a treadle valve problem.

What air pressures are you seeing?