What does this lever do in my M1088?

[Reworked LMTV]

Hi Guys,
I'm working on my M1088. I think this is an air valve of sorts. What does this lever (with the black ball on top) do? : )

 

[gimpyrobb]

Probably a trailer brake control. Is it a tractor?

 

[Johno176]

Yes that is a trailer brake control valve on the M1088. It allows the driver to manually apply extra breaking force to the trailer above what is supplied via the brake pedal.

 

[Floridianson]

Rerouted mine from trailer to passenger eject seat.

 

[KsM715]

Yes that is a trailer brake control valve on the M1088. It allows the driver to manually apply extra breaking force to the trailer above what is supplied via the brake pedal.

Are you sure about this? Does it apply more braking power above what the foot pedal applies? Or does it apply the trailer brakes without using the foot pedal in the truck? That way you can lock the trailer brakes to hold the trailer in place while you're hooking up or dropping the trailer. Or moving the position of the trailer wheels if the trailer is set up that way.

 

[lmtvjunky]

Trailer brake controller, when you loose control of a load or feel the trailer is getting outta control this will apply brakes to the trailer and straighten you out, just like your trailer brake control tabs in your standard truck

 

[Floridianson]

Are you sure about this? Does it apply more braking power above what the foot pedal applies? Or does it apply the trailer brakes without using the foot pedal in the truck? That way you can lock the trailer brakes to hold the trailer in place while you're hooking up or dropping the trailer. Or moving the position of the trailer wheels if the trailer is set up that way.

Agreed I don't believe it would put any more braking force then the foot brake at full peddle. I use mine like you said when hooking up or fifth wheel adjustment. Yes with small trailers on the hook not fifth wheel plate if the load is not correct or the tonque weight is not correct the small trailers will wag so applying the hand brake/elect controller it will stop the wag.

 

[Reworked LMTV]

Rerouted mine from trailer to passenger eject seat.

Hmmm there's label below it that says: "N. Korea, Care Package, much love, US Army"

 

[Johno176]

yes controller applies air to trailer brakes indendent of the foot pedal. So for any position of the foot pedal, the hand trailer brake control can apply extra breaking force(up to full on with foot pedal).

 

[lmtvjunky]

Agreed I don't believe it would put any more braking force then the foot brake at full peddle. I use mine like you said when hooking up or fifth wheel adjustment. Yes with small trailers on the hook not fifth wheel plate if the load is not correct or the tonque weight is not correct the small trailers will wag so applying the hand brake/elect controller it will stop the wag.

Exactly, straightens the wag or fish tale, most people with extensive tow experience has to have this feature, down hill is the worst

 

[Floridianson]

yes controller applies air to trailer brakes indendent of the foot pedal. So for any position of the foot pedal, the hand trailer brake control can apply extra breaking force(up to full on with foot pedal).

Yea You said it correct, independent of the foot peddle up to full on braking force same a peddle. Some independents with there own tractors and pulling a trailer that was not there's would use the trailer brakes and save the tractor's in some cases.
The wag seems to be more problem with ball hitch trailers and as said not correct distribution of weight on tonque.

 

[Tga]

The trailer service brake control lever ("johnny bar" in trucker lingo) has many uses. Most all of the examples given so far are true. The lever is used to control the service brakes not the emergency brake (also referred to as parking or spring brake system) on the trailer. It can input 0-120psi (or whatever full psi is at any certain time) and is independent of the foot pedal. It can be used independently of the foot pedal or in conjunction with the foot pedal, but can only add to the psi being applied by the foot pedal (to the trailer service brakes only) not decrease applied psi. It's use during attaching or detaching a trailer is not practical since you typically would have air lines detached during those operations. Some of the most common uses (not necessarily in order) would be:
1. Testing fifth wheel/king pin connection. (Could also be tested using trailer parking brake)
2. Testing trailer service brakes. Helps driver to feel and evaluate adjustment, air lag, and sensitivity of trailer brakes. Each trailer is different and knowing how the trailer brakes are going to react (or not react) is good to know.
3. Sliding trailer tandems. Also can (and usually is) be done with trailer parking (emergency) brake set, but is sometimes necessary with heavy loads, stubborn (poorly greased) tandems/rails, or weak parking (spring) brakes.
4. Supplemental braking. If you have poorly adjusted trailer brakes or poorly distributed weight (heavy on trailer tandems, light on kingpin) extra air pressure can be applied (over and above foot pedal) to trailer which will facilitate a shorter safer stop.
5. Holding vehicle on incline. Used to hold vehicle on incline (in traffic or the like) to prevent vehicle from rolling backwards while engaging clutch. Do not use as parking brake! Most will not stay engaged without input from the driver and will slowly disengage due to air pressure on other side of valve if not physically held in place.
6. Emergency bypass of tractor brakes. If a catastrophic failure (blown service air line) of the tractor service brakes occurs
trailer brakes can be used independently to stop vehicle and/or get vehicle to safe place without depletion of air pressure.
7. Preventing jackknife. If tractor drive tires loose traction (typically during mid-high speed cornering on off ramps or the like) and the trailer is "pushing" the tractor the trailer service brakes can be applied to "pull" the tractor straight.
8. Controlling "wag" (as put in previous post). Typically not a big problem with a fifth wheel trailer unless weight distribution is WAY off on a single combination vehicle but is used fairly often to settle down a set of doubles (they are called wiggle wagons for a reason).
9. Isolating air leaks. If you have an air leak in your service brakes you can apply air to trailer only and watch air gauge for reduction in air pressure, if none, then you have isolated leak to tractor.
Obviously there can be other uses and all these examples may not be applicable to all situations/vehicles but are the most common and practical applications in my experience.

 

[Floridianson]

Don't agree on hook up of trailer. Most older military trailers do not have spring parking brakes and they can move if you bump them.

 

[Tow4]

Don't agree on hook up of trailer. Most older military trailers do not have spring parking brakes and they can move if you bump them.

On the older air over hydraulic brake trailers such as M-146, you should air up the trailer first. Once the trailer air system is charged, the brakes work like modern spring parking brakes until the air leaks down.

 

[Tga]

Don't agree on hook up of trailer. Most older military trailers do not have spring parking brakes and they can move if you bump them.

Being in the "Present Conflict Vehicles" category and FMTV topic I was referring to modern air brake equipped vehicles/trailers ,both military and not, not older air/hydraulic or other vehicles/trailers. To the best of my knowledge the modern semi trailers, Ammo trailers, LMTV and FMTV trailers are equipped with spring parking brakes. Wasn't trying to step on any toes, just sharing my experience with heavy duty air equipped vehicles, but there are always exceptions. As I stated in previous post:
Obviously there can be other uses and all these examples may not be applicable to all situations/vehicles but are the most common and practical applications in my experience.

 

[Floridianson]

On the older air over hydraulic brake trailers such as M-146, you should air up the trailer first. Once the trailer air system is charged, the brakes work like modern spring parking brakes until the air leaks down.

Correct you air up the trailer first. Not like the modern systems that need air to release parking. We need air to apply parking so tank needs to be filled or have plenty stored and holding. No air no brakes parking or moving. This also works as the brake away system as long as the tank holds pressure.
The air over Hyd. is good and bad. They way they are if you had to move fast you could hook, open trailer air tank and leave no air lines. With the newer systems you need to air up first and if you were in a rush plus had a bad chamber and it needed to be caged you could not move till caged. Yes I rather change out my axle to S cam straight air which has been done.

So in theory we hook to a Air/Hyd. system with working tractor, air lines first. Air up and use the hand brake before going under for safety first. Don't rely on just the trailer air tank and valve to hold the trailer.
Now lets say you are hooking to a straight air trailer but someone has caged all the brakes and not told anyone. You back under to hook and she rolls into something expensive. To be safe always check the brakes are set or working before you back under to hook. Don't be lazy.