PTO wont engage

[FLJohnDeere420]

I've been having a problem with my front PTO . When I start the tractor (some of you would call it a mower) the PTO will start fine and off I go mowing like a champ. Recently if I turn the PTO off or if the motor freakishly stalls I can't get the PTO to engage, but if I try again the next day it engages and off I go.

I've checked the power going to the PTO clutch and it has 12.5 volts. My dad and I think it might be a safety switch, maybe gets rattled and shuts the motor down. Maybe its stuck and wont let the PTO re-engage. I'm not sure if thats really it or not, I looked all over for the safety switches and thus far I have only found the one for the starter (making sure the tractor isn't in fwd or reverse).

Any hints will be gratefully accepted.

Here are the specs:
Model: JD 420
Motor: Onan (I think 20 or 22 hp)
Deck: 60"

Thanks and look forwards to the ideas.

 

[Willl]

I've checked the power going to the PTO clutch and it has 12.5 volts.

If you have power at the clutch, it should engage.
I can't believe it's a safety switch, if it was you wouldn't be able to get power to the clutch in the first place.

I'm betting it's a bad clutch.

 

[Willl]

If you have power at the clutch (and ground), it should engage.

...............

 

[Willl]

Another thought, could be a bad connection that's letting just enough voltage for your meter to read but drops out when higher amps are needed.

Try disconnecting clutch power and running a direct wire from battery.

 

[FLJohnDeere420]

Heading out to try that now. I'll post an update in a bit. Thanks for the idea and I hope its not the PTO clutch, I hear they can be a couple hundred

 

[FLJohnDeere420]

OK, so I think you were right about the amp drop over the wire. It just doesn't make sense to me that it would work initially and then not work 40 mins later after use. Maybe the switch is getting cooked? I put 12 V to the PTO wire when the switch wouldn't engage it today and wamo it works. Thanks for the idea. I'm going to replace the entire cable later this week.

I found out the reason for the engine cutting out was **** ethanol fuel, drained some out and it looked like crap, wasn't even that old. I'm adding Startron to every gas tank and vehicle I own now.

I'll update when I get everything working and if I find any more bugs.

 

[ccsial]

One other quick test you could do is put a jumper wire across the switch and see if it engages. The switch, or the connections to it, could have high resistance too.

 

[Dutch445]

If it's not restarting while hot, it could be
a gap issue in the clutch. As the clutch wears,
the gap gets larger and larger. Eventually, you will
notice the PTO won't restart while hot, because that gap
is too big. I think there are 3 nuts around the clutch that allow
for gap adjustment, with springs between the plates.
I don't know the recommended spec right off, but that
may be where the problem lies. Tighten each nut equally till
you reach the proper gap spec and you may find everything is ok after.
let us know

 

[Dutch445]

did a little digging, here is the airgap spec:

AIR GAP SPECIFICATION IS .012-.020 INCH (0.3-0.5 MM). .016 INCH
(0.4 MM) IS PREFERRED SPECIFICATION.

 

[FLJohnDeere420]

Thanks for the ideas, I'll check both the spacing and the resistance in the other wires tomorrow night. Unfortunately work is getting in the way of working on the tractor this evening.

I'm thinking if it is the resistance that I might have to re-wire the whole tractor. Not to big of a deal but when I get into a wiring job I usually get a little OCD. I'll update tomorrow night after some tinkering.