855 PTO will not operate

[855guy]

for past 2 yrs PTO has been intermittent. Last yr I replaced the saftey switch under the seat, helped for a while. Several times this year it has acted up again. I would fiddle with the switch and/or wiggle the wiring and it would eventually work. Last Fri. while running the brush hog, a limb bumped the on/off lever and disengaged the PTO. I got off the tractor, picked up my hat and got back on and PTO would NOT engage. I got off, lifted the seat, pulled the safety switch up and PTO started, put the seat down and nothing. Did this again, same thing - worked with set up, would not work with seat down (me on it). Hasn't worked since. I have tested the switch - meters o.k.. Have checked the wire best I can all the way from seat switch to the dash PTO lever - all seems o.k.. All connections seem good. I don't find and fuses.
Unit is a 1988 and has 1077 hrs on it.


ANY IDEAS?

[unimog_jason]

855guy,

When I first received my 755 back in January the PTO would only engage intermittently and was a cause for great concern. After a little digging I found the electro-magnet that connects the PTO level to the rod that engages the PTO wasn't getting full power. In my case I just cleaned all the terminals up and bench tested the magnet with a battery charger to ensure everything was up to spec and put it back together and it's been working great.

Another thing I did do was lube up all of the rod pivots, the previous owner didn't lube anything up so things were binding a little bit.

I would jumper the seat switch, open the hood and you should be able to look in through on the side under the dash and when you push the level forward, you should see the two parts travel together, remove the jumper and they should separate. If this isn't happening you may want to check your connections and make sure the magnet is functioning correctly.

Hopefully this helps you.

Jason

[855guy]

Jason,
Thanks for prompt post.
Great idea - unfortunately mine isn't that simple.
However you got me past several of my unknowns. I understand now what the magnet does and the function of the rod connected to it. I have NO power to the magnet, regardless of where the safety switch is. This leads me to believe I have a wiring issue someplace.

Anyone have a wiring diagram for a 6/7/855 or where to find one?

[855Idiot]

My 855 will "loose" power to the PTO too. I have found it's the magnetic switch disengaging it's self.

I was brush hogging last weekend and noticed that when the brush hog would strain, the PTO switch would disengage.

I just reset the dash lever and it would be happy again until the next time...

It seems as though I have to lift the lever slowly to make it work right.

Good luck,

Why is the switch magnetic

[855guy]

Not having the schematic of the PTO functions - I would speculate the electro magnet is energized all the time the tractor is running WHEN the safety switch(s) are made (far as I know there is only one under the seat - that works all the way out or all the way down in to make the circuit complete to the magnet).

With the safety switch 'made' the circuit is complete and the magnet will hold onto the handle and pull up the arm that really engages the PTO.

When mine worked - I never had a problem with it staying 'engaged' regardless of what bumps I hit - lawn mowing or mowing with the 5' brush hog. Maybe your magnet is either dirty (as was mentioned earlier) or getting week, time for a replacement (easy to get to on my 88', just pull the side cover and one bolt to remove the arm and a cotter pin in the rod, disconnect a plug and it is in your hand).

[unimog_jason]

You can try applying power directly to the magnet to help eliminate it, outside of that it could be the relay that acts as a delay so that if you bounce in your seat the PTO won't disengage.

I have a diagram around here somewhere, I'll scan it and send it over to you in the morning.

Jason

Originally Posted by 855guy

However you got me past several of my unknowns. I understand now what the magnet does and the function of the rod connected to it. I have NO power to the magnet, regardless of where the safety switch is. This leads me to believe I have a wiring issue someplace.

Anyone have a wiring diagram for a 6/7/855 or where to find one?