Brake Lights On too long

[m139h2otruck]

My son noticed that the brake lights on the water truck seem to stay on for an extended period after the pedal is released. I confirmed this in the yard with a mirror on the step ladder, and removed the breather on the top of the switch and added a shot of air tool oil to the switch. Also added oil to the air booster per the manual (have done this before). Seemed to be OK, just a touch sticky. However, after moving the truck to a job in Hooksett, and following our driver back to the job with a full load of water (heavy!!!) the brake lights stayed on for over 30 seconds or more. Any ideas??

Both the front and rear glad hand fittings have been removed and solidly capped. Would this make a difference?? Have a new switch from ODIron that I bought to use in the sprag air line for a reverse alarm switch, but it is different than the existing original switch, without the vent and mounting feet.

 

[rmgill]

Could the vent line be blocked? If that's the case it may not be letting the air vent easily. Extra pressure on the air pressure switch could be enough to trip it but not enough to put useful pressure on the brakes.

 

[m139h2otruck]

Which air vent? The master cylinder is vented through some sort of vent system (to the air cleaner I think). Is the air booster vented the same way? Brakes do not hang up or drag at all. There was a post about the glad hands needing venting or else something happens. This is why I noted that ours are capped off.

 

[bugei]

doesn't that sound like a bad (sticky) switch, as opposed to a brake problem? can you hook a ohm meter to the switch with no wires hooked to it, and see if it is just a "draggy" switch.

sorry if this is somehow crazy, just a thought from an electronics geek.

 

[rmgill]

The switch closes with a few PSI of pressure if I'm not mistaken. IF the pressure which is 120 PSI or so takes some time to vent throught he vent system then it may take a second or two to open the switch. More so if it had fresh oil in the vent line that prevented it leaking down quickly.

The air pack has a vent line that joins up with the master cylinder AND another vent line from the fuel tank. The single unified line then runs to the road draft tube (slobber pipe) off the side of the engine.

There's an MWO to split the vent lines and have the brake system lines run to a breather up on the firewall.

 

[acetomatoco]

I would check the MC for a lazy return.. there is probably crud in the system.. the hydraulic switch on the MC was replaced by a Air one.. by MWO and it could be full of water.. drain those air tanks... when the brake lights are on... you have thirty seconds you say... have a wrench on one of the wheel cyl bleeders and open it and see it the brake lites go off..sure sign of residual pressure in the hydraulic side...

 

[m139h2otruck]

The brake switch is on the air side of the system (stock), and we have not noticed any dragging of the shoes or heating of the drums from a sticky MC. Air tanks are drained every day, and water has not been a problem.

 

[mangus580]

I have this problem on my deuce as well. Although mine coincides with a switch change. I went from a switch that would hardly ever turn the lights on.... to one that doesnt like to turn them off. go figure!

 

[m139h2otruck]

Following truck again today on the road (loaded with 4,000 gallons of river water or 33,300#) and the brake lights still stay on for over a minute after the driver lets off. Air tanks are empty of water & MC not dragging. Have noticed on new tractor that right front glad hand cover has a vent like the transmission and TC that lets air out but not in. The water truck's front air connections are capped off, should the right hand one on the front have an air release vent?

 

[acetomatoco]

Yes, the right front one needs to be vented... early ones had the little cap vent, like an axle vent, and later ones just had a hole drilled in em... There is a check valve further back in the system which opens when you pressurize that glad hand to apply the brakes on the towed truck... if a little air leaks past the checkvalve it is unable to get past the glad hand to vent and pressurizes the main system by default...and viola your brake switch thinks the brakes are on.. and it is not enough to apply the brakes...I have had 5 tons fail to move because of this malady...some folks claim not to have any trouble, but that is because they have a nice check valve...which probably just needs some exercise on your unit...

 

[m139h2otruck]

Thanks, I thought that there had to be a good reason why the glad hand had a vent. Will try and vent the line and see how the lights act then.

 

[m139h2otruck]

Will try drilling a pinhole in the plug we put in the right side front air line to see if this works. We don't go fording with the truck so a pinhole should work OK.