Trailer decoupling problem

[Glen Donnach]

I have a 915A1, and 2 M871 trailers. I have a continual problem on both in getting them unhitched. I can pull the release lever out about 2 inches, see the mechanism move out but never enough to decouple. I eventually get it done by moving forward,backward numerous times and by magic it will eventually let go. Not sure why it decides to work or why it doesn't work smoothly every time.

Does anyone have the same problem or know what the issue might be?

Thanks,
Glen

 

[doghead]

Are you on level ground(side to side)?

Have you tried, after disconnecting airlines(setting trailer brakes), do you back into the trailer a bit?

 

[Nonotagain]

Sounds like you might need to pull the hitch plate apart, clean and lubricate it and re-install everything. Also make sure that the apron is greased because if they are dry and are a pain to pull out from under a trailer.

Second thing to check is that the trailer and tractor is level or atleast both on the same plain. When you crank the landing gear down the truck should ride up a good three or four inches from loaded height.

 

[Glen Donnach]

Decoupling

Thanks for the replies so quickly. I do usually try to backup a bit to ease the pressure. Hasn't worked the last couple of days. It is not a perfectly level spot, but not too bad. How much should I crank up the jackstands?
If nothing else works, I guess I can haul it to a paved parking lot. I live in the country so not much pavement in my neighborhood
Should I see light under the plate or is that too much lift

Thanks,
Glen

 

[kc5mzd]

If the trailer is empty and the truck does not have air suspension you should crank the landing gear down till it just touches the ground. If you start to lift the truck you might end up putting pressure on the pin and the locking mechanism.

 

[M813A1]

Just remember to lift the safety latch on the front of the fifth wheel plate as you pull the main release !! It will make it hard to un-hook if you do not lift the safety latch !! Try that it is far easier then removing the fifth wheel on play wih the latching mechanism

 

[Scrounger]

It sounds to me what you are having is a release problem. The fifth wheels on military tractors doesn’t usually get used enough to wear out. The problem you are experiencing sounds more like a lube problem. Besides lubing the top of the fifth wheel with grease the underside parts also need to be lubed. We use SPL100 to lube the stuff on our fifth wheels at work. Any lube like it will work. First you need to lube all of the pivot points where the linkage is under the front, and then lift the back up; a 2 foot long piece of metal or wood comes in handy, so you don’t get the grease on you. Then lube the underside from the back. If the grease in the jaws of the plate look like it is hardening up from lack of use spray some lite lube in there to free things up. After lubing the fifth wheel couple and uncouple from a trailer a couple of times to spread things around.
When dropping a trailer the landing gear should just touch the ground.

 

[wreckerman893]

If the trailer is loaded you need to crank the legs down to where they take pressure off the 5th wheel ( there is a LOW and HIGH gear for the landing gear)......if it is empty you can just lower it until the legs make good contact and slide right out from under it.

 

[kc5mzd]

Just remember to lift the safety latch on the front of the fifth wheel plate as you pull the main release !! It will make it hard to un-hook if you do not lift the safety latch !!

When I got my tractor I tried for a couple of days to get it unhooked without moving the saftey latch. Finaly I gave up read the TM and decided to go ahead and try lifting the saftey latch - It made it a lot easier...

 

[Floridianson]

Yea same here I have to take some pressure off the plate loaded or empty.

 

[Floridianson]

When I got my tractor I tried for a couple of days to get it unhooked without moving the saftey latch. Finaly I gave up read the TM and decided to go ahead and try lifting the saftey latch - It made it a lot easier...

What truck do you have. The plate on the 915 is different than on the 818.
We have a small pull and big pull leaver. Not the swing trap door style.

 

[jimk]

Usually the handle needs to go past the safety catch then lifted to hook on the edge of the opening. It helps to keep the 5th wheel surface greased. A dry 5th wheel can also cause erratic/dangerous steering behavior (ex-understeer snaps to oversteer).

 

[Glen Donnach]

Thanks for all the tips. I removed a bunch of built up gunk, oiled and greased everything, raised the trailer just a tad, and it worked first time. I think it was a combination of many things but the gunk buildup and very little grease kept it from working correctly. I have not owned the truck very long and I should have done that first thing. Thanks to everyone for the wisdom. If you ever get stuck in Mid Missouri, and need a favor, keep me in mind.

 

[fasttruck]

In snow season keep the tractor under a trailer or cover the fifth wheel jaw with something to keep snow out of the jaw. The presense of snow in the jaw could resujlt in a false lock up of the jaw with the subsequent release of the trailer at speed. Very embarassing: landing gear fold up, air and electric lines break; try and figure out how to raise the trailer top recover it etc. If the combo was last moving forward the king pin will be in the rear of the jaw which puits pressure on the latch and makes uncoupling difficult. As others have suggested backing up to get the pin in the front of the jaw will usually solve the problem. You are allowed 1/2" slack in the jaw.

 

[Stan]

No daylight between the fifth wheel and the trailer.

 

[Old Lincoln County Iron]

Have any of you all used Lucas 5th wheel and slider lubricant? Just curious I haven't found anyone thats using it, to get thier input on it. Thanks!

 

[powerhouseduece]

I had similar issues with the 5th wheel on my m818. The truck has the m915 style 5th wheel on it when I got it. My problem was when trying to unhook from my m127a2c, I had to leave the trailer brakes hooked up (air/hydro brakes) and have someone pull the latch handle while I backed up a little bit causing the jaws to release. I would then pull forward a inch or 2, unhook the air lines and pull out. After all that I decided to pull the 5th wheel off and bob it