JD 770 Can't engage PTO

BikeSanta · Jan 2, 2015

diesel466 said:
On the right side of the clutch housing is a screen that you can remove to see clutch, You have to remove the plastic panel down by your feet. I would try engaging the pto with the engine off and have someone hold clutch pedal down and see if you can turn the pto shaft by hand.

diesel466 - Thanks to the tip from jd110, I bypassed the correct interlock and can easily start the tractor with rear PTO engaged. I removed the screen on the right side of the bell housing and can see both clutch disks. With the engine off, the clutch pedal clamped all the way down and the rear PTO engaged, I can't turn the PTO by hand. Both clutch disks appear to be about the same thickness. The main transmission clutch disk has about .030"+ of float, and can be moved back and forth. The PTO clutch has no space on either side and can't be moved.

From looking at the transmission diagram, it appears that the throw-out bearing is likely of the carbon variety, rather than the ball bearing type. If so, it might be the throw-out bearing that's shot. The operation of the 2-stage pressure plates is a mystery to me, but even a worn pressure plate shouldn't cause this problem.

So, I'm back to the premise that either the PTO clutch is frozen, or I can't get enough clutch travel to disengage it, possibly due to a worn throw-out bearing. Either way, it's likely that I'm looking at splitting the tractor in the spring.

beenthere · Jan 2, 2015

Bike
Looked up a schematic of the dual clutch engaged and disengaged on the tech manual and will post the two. Hope it helps your figuring. Now that you can get the tractor started with PTO engaged, maybe put some attachment on the PTO to try to break loose the PTO clutch. May not take much. I assume a tool (long screw driver?) can't be pushed through where you see the PTO clutch plate tight together?

BikeSanta · Jan 4, 2015

beenthere said:
Bike
Looked up a schematic of the dual clutch engaged and disengaged on the tech manual and will post the two. Hope it helps your figuring. Now that you can get the tractor started with PTO engaged, maybe put some attachment on the PTO to try to break loose the PTO clutch. May not take much. I assume a tool (long screw driver?) can't be pushed through where you see the PTO clutch plate tight together?

beenthere - Thanks for these diagrams. They do help me understand what's going on. I did poke around with a screwdriver, but I was a concerned I might cause a biggrer problem. I tried breaking loose the clutch by clamping the clutch down, engine off and rear PTO engaged. I grabbed a hold of my snow blower second stage impeller and tried turning the PTO. I could turn the PTO shaft a little, and I could see through the access hole in the bell housing that I was turning the whole clutch/flywheel assembly. But I could not break the clutch free. I could just turn it back and forth a few degrees. I may try a longer lever on the PTO if I can think how to make one up. Thanks for your ideas.

jd110 · Jan 4, 2015

I

had forgotten there is a screen on clutch housing on the 770. On the 870, 970, and 1070 I have adjusted The pto though the holes in the clutch housing. I am attaching the picture of the adjusting screws. If you can see theses screws (3 of them) through the hole and can get wrenches on them to adjust them, you can get it fixed without splitting the tractor. Adjust these three screws to .060" under the head of the bolt. You will probably find this clearance now more than that.

pmsmechanic · Jan 4, 2015

If you can see that the pto clutch is releasing then I'm thinking that the clutch disc is rusted onto the flywheel. If that is the case then forcing a strong pointed knife between the flywheel and the clutch disc while holding the clutch pedal down might be enough to release it.

BikeSanta · Jan 5, 2015

jd110 said:
IView attachment 405426 had forgotten there is a screen on clutch housing on the 770. On the 870, 970, and 1070 I have adjusted The pto though the holes in the clutch housing. I am attaching the picture of the adjusting screws. If you can see theses screws (3 of them) through the hole and can get wrenches on them to adjust them, you can get it fixed without splitting the tractor. Adjust these three screws to .060" under the head of the bolt. You will probably find this clearance now more than that.

jd110 - Thanks for the photos. Very helpful. I might be able to get to those bolts. I haven't figured out how to turn the assembly more than just a little using the PTO. If it were a gas tractor, I'd take out the plugs, but with the diesel, hand-turning the engine is a problem. We're going to have a few days of very cold, bad weather, and I'm working outside. When the weather improves a little, I'll give this a try. I might be able to "bump" the engine around with the starter. I saw that your photo is from the TM1470 manual. I went ahead and ordered the manual on CD from John Deere. Thanks.

BikeSanta · Jan 5, 2015

pmsmechanic said:
If you can see that the pto clutch is releasing then I'm thinking that the clutch disc is rusted onto the flywheel. If that is the case then forcing a strong pointed knife between the flywheel and the clutch disc while holding the clutch pedal down might be enough to release it.

pmsmechanic - Thanks for the suggestion. I don't have much space to work in, but I did try to put a thin tool in there - much thinner than a screwdriver. I discovered that there was no space on either side of the PTO clutch disk. So if the disk is rusted to the flywheel, it's rusted to the PTO pressure plate as well. Thanks for your advice, but I don't think I'm going to get anywhere with that. If I can turn the assembly to where I can see the bolt heads, as suggested by JD110, I can at least see if they are adjusted correctly.