Brake problem

[Z71]

I have had no problems with brakes on my M109 for many years until today. I drove the truck around my yard, when suddenly two things happened:

1. The pedal started sinking to the floor and when I pumped it, it became firmer again, but I heard hissing noise from under the truck which sounds like an air leak somewhere.

2. I smelled and saw acrid electrical fire smoke coming from under the truck and noticed that the brake lights stayed on even with the brake pedal released. It seems that the brake light switch shorted out and burned up, or something similar.

So what happened? Did my air pack go out and needs to be replaced, or is this just an air leak from the supply hose? I have not had the chance to check it out yet as it got dark qukcly. Where is the brake light switch located?

If I need the air pack, is it best to buy a new one, used one or rebuild the existing one? Who has a good price on one, or the rebuild kit? What about the brake light switch?

I am happy this did not happen on the road somewhere.

I appreciate any help on this.

 

[porkysplace]

The TM would be a good place to find the the brake light switch.

 

[Z71]

I found that the brake light switch is located on the air pack itself. It looks like it is a pressure switch. Is it possible that it failed and caused the air leak I heard? I hope that is all it was. Where can I find a new stop light switch?

 

[castirondude]

I know the low air pressure alarm switches can do this, they will leak air and the alarm will stay on. I haven't had them burn up, actually they can't because they just ground the wire from the buzzer.
Could you not just feel around with your fingers to find the air leak? This is why these trucks have a fire extighuisher, to hold the brake pedal down while you chase air leaks

 

[Z71]

I got under the truck, found the brake light switch on the air pack, it sure enough failed, there is burned smell in that area. I found a new switch on eBay, hopefully that is all it was. Since it is a pressure switch, if it fails internally, it will cause an air leak from the air pack.

 

[porkysplace]

Time to upgrade to a air switch , do a search plenty of threads on them and the parts needed.

You said in post #1 you have had the truck several years , when was the last time the brakes were inspected or serviced?

 

[welldigger]

Yes the air switch failing can cause an air leak. Not 100% sure that explains the pedal going soft tho.

 

[DeucesWild11]

What porkysplace said, do the upgrade on the switch so if it fails again you won't loose your brakes.

 

[Z71]

Can you explain the switch upgrade? The present switch is an air pressure actuated switch with two electrical leads. I think the switch had an electric short in it and burned, causing an air leak, enough to cause a soft brake pedal for a moment.

What does the "upgraded" switch look like?

 

[porkysplace]

Can you explain the switch upgrade? The present switch is an air pressure actuated switch with two electrical leads. I think the switch had an electric short in it and burned, causing an air leak, enough to cause a soft brake pedal for a moment.

What does the "upgraded" switch look like?

When you search for " brake light air switch " this is the 8th thread that comes up . Read it , it will answer your question.
Brake Light Switch burned to a crisp

 

[Z71]

It looks like the air pack is leaking brake fluid through the damaged switch (still installed at this point). I tried to unplug the electrical connector, but the whole switch body broke off inside the connector, as it was partially melted from heat. If there is brake fluid leaking from the damaged brake pressure switch, does the air pack need rebuilding? Or, is the brake switch actuated by pressurized brake fluid? If that is the case, then there should be no issue with the air pack.

The brake pedal was nice and firm for years until the brake switch failure yesterday. This does not mean that the air pack did not fail internally at the same time, i.e air got into brake fluid. However, if this happened, then the brake pedal would probably sink to the floor and stay there.

 

[gimpyrobb]

There is 2 places for your brake switch on a deuce. Originally, they were installed at the front of the airpack where fluid came out and the pressure of the brake system would activate the brake switch. That is a bad place as it will break and sometimes you will loose your brakes. The other newer spot is on the air side of things. That way if the pressure sensor fails, you won't loose your brakes. This is an MWO (modification work order). It is supposed to be done to all the trucks.

Where is your switch located? If its on the front of the airpack, it should be moved.

 

[steelandcanvas]

The replacement MWO kits can be purchased from Jay at Saturn Surplus.

 

[Z71]

There is 2 places for your brake switch on a deuce. Originally, they were installed at the front of the airpack where fluid came out and the pressure of the brake system would activate the brake switch. That is a bad place as it will break and sometimes you will loose your brakes. The other newer spot is on the air side of things. That way if the pressure sensor fails, you won't loose your brakes. This is an MWO (modification work order). It is supposed to be done to all the trucks.

Where is your switch located? If its on the front of the airpack, it should be moved.

It is located on the front end of the air pack. Thanks for the explanation.

 

[DeucesWild11]

Here is a pic of what the new switch should look like. You can see the big nut at the end of the airpack has been capped off, that is where the original switch was. This should help you determine which one you have. Now my hookup may look a little different because I don't have an airline running to the rear of my truck for a glad hand so there would be another T off in there somewhere.

 

[porkysplace]

It looks like the air pack is leaking brake fluid through the damaged switch (still installed at this point). I tried to unplug the electrical connector, but the whole switch body broke off inside the connector, as it was partially melted from heat. If there is brake fluid leaking from the damaged brake pressure switch, does the air pack need rebuilding? Or, is the brake switch actuated by pressurized brake fluid? If that is the case, then there should be no issue with the air pack.

The brake pedal was nice and firm for years until the brake switch failure yesterday. This does not mean that the air pack did not fail internally at the same time, i.e air got into brake fluid. However, if this happened, then the brake pedal would probably sink to the floor and stay there.

It's pretty clear with this post that you didn't bother to read the thread posted in post # 10 . You have had this truck for 13 years from what you posted in another thread . You really need to make a effort to at least look at the information you are asking for . And after 13 years of owning a deuce you should have basic knowledge of how to use a Technical Manual . Since you necer answered my question when the brakes were last inspected or serviced I'm going to take that as never in the last 13 years . People are more than willing to help here , but you need to make affort to help yourself . All your doing is wasting peoples time , when you don't even make a attempt to look at the parts manual so you know what the parts they are telling you to check .

 

[Z71]

It's pretty clear with this post that you didn't bother to read the thread posted in post # 10 . You have had this truck for 13 years from what you posted in another thread . You really need to make a effort to at least look at the information you are asking for . And after 13 years of owning a deuce you should have basic knowledge of how to use a Technical Manual . Since you never answered my question when the brakes were last inspected or serviced I'm going to take that as never in the last 13 years . People are more than willing to help here , but you need to make affort to help yourself . All your doing is wasting peoples time , when you don't even make a attempt to look at the parts manual so you know what the parts they are telling you to check .

Wow, you are making a bunch of conclusions that are just wrong. I did read the post that you linked and it took me a while to figure out that these switches are actually different - the one that works off of pressurized fluid is fluid activated, the other is just an air pressure switch. They are not the same switches and should not be simply relocated. The modification kit comes with an air actuated switch. This was not clear at first.

I removed the leaky switch from the truck, refilled the master cylinder, plugged the switch hole with a bolt, ordered the correct switch which I will install and bleed the brakes to get the brakes working. Then I will consider doing the switch mod.

As for doing maintenance on the brakes, the truck had extremely low miles (less than 1000 original miles and it is a shop van) when I got it and the brakes were all in excellent shape. I did not put too many miles on the truck, so I never replaced any components, although I should have checked them after 5 years or so. That was a neglect on my part. I typically change DOT3 hygroscopic brake fluid on my car and truck every two years and replace the brake hoses every 8 years or so. I also rebuild the calipers if I keep vehicles this long.

 

[doghead]

Bolt?, The hole is pipe thread.

 

[emr]

Actually porkysplace is right on it big time. You did not give an answer, and I was thinking the very same thing, really? You have had the truck how long and still havnt done any home work on the simple things like brakes and a few others? Not busting hard to be bad, Just letting you know He is 100% correct. You have a good answer , but what maintenance did you do then ? Do you know what maintenance to do ? One should pull all the wheels and drums and inspect, its a great learning experience, wheel cylinders can weep and not be noticed for a long time, and be very dangerous, Your truck should have a " Major brake adjustment and then keep a record because a minor is due in 3000 miles then 3000 more another major " All brake info in this site, Good luck,

 

[welldigger]

Bolt?, The hole is pipe thread.

Ya I was kind of thinking the same thing. On another note where the air switch is depends on which air pak you have. If you have the short style the air switch is in fact on the front.