M939, what are the air lines on the park brake doing?

[racing4funn]

I have one truck that then applying the park brake I can hear the air blowing off (brakes?) but my other truck that everything seems to work, has no air sound, nothing.

 

[davo727]

I thought it dumps the air out of the spring brakes which locks them up.

 

[doghead]

It does, but through a relay valve, Your valve may be bad.

 

[doghead]

Just get under the truck and find what is letting air out.

 

[LiqTenEXp]

Mine too sounds like it lets the air out when applying the parking brake. Anyone have a good explanation of the air circuit involved in this?

 

[doghead]

Look at the parts TM?

 

[Gunzy]

It is supposed to let air out. It dumps the air off of the spring brakes into the intake stack and can be a little noisy. Mine sounds like the trick has got gas and is relieving itself. My friend calls it the fart monster.

 

[MtnSnow]

Yep...Pulling that parking brake lever is like pulling grampa's finger! Just like it's supposed too! If it's silent then the parking brake is applied then it probably is not venting the spring brakes like it should and thus you are only getting the benefit of the single brake band that is cable activated at the rear of the transfer case.

 

[doghead]

So, the question is, did the OP mean air is sounding continuously or just for a few seconds.

 

[LiqTenEXp]

I hear a "fart" sound out of the intake stack. Guess mine is ok!

 

[MtnSnow]

Good question Doghead.... Yep if it's the momentary fart/venting that's proper but if it's continual or non-existent then something is amiss

 

[wheelspinner]

On the one that is NOT expelling air, make sure the spring brake over ride knob is pulled OUT to normal. If its pushed in the spring brakes get a constant supply of air and will never set.

 

[MtnSnow]

Good call Wheelspinner.

 

[Floridianson]

Agreed she should be farting.

 

[racing4funn]

On the one that is NOT expelling air, make sure the spring brake over ride knob is pulled OUT to normal. If its pushed in the spring brakes get a constant supply of air and will never set.

DING DING. Chicken dinner. I never push it so I never thought of checking it.. My little one was in there and likes to push buttons.. he is only two year old but has already started pushing my buttons.

 

[Floridianson]

Hope you will be checking everything from now on as that could have ended different.

 

[wheelspinner]

This is a great thread for those who don't really understand the air brakes in these trucks. If that little knob is pushed in, which those who know air brakes would probably do from muscle memory, the truck will only be parked on the little manual parking brake on the drive shaft. That is assuming that is adjusted correctly. That knob is ONLY for an emergency release of the brakes in the case of a catastrophic loss of air to move from an emergency situation, i.e. stuck on rail road tracks or in the middle of an intersection. Other than that it should ALWAYS be out and never used for any purpose.

 

[doghead]

Is that in the -10?

 

[doghead]

If letting 2 year old kids play inside of big trucks was a good idea, don't you think every daycare center would have one of these things?

 

[Floridianson]

If letting 2 year old kids play inside of big trucks was a good idea, don't you think every daycare center would have one of these things?

That's pushing it a bit but yes when they are done playing all things should be check to see if something might be amiss.