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Pto rebuild gone wrong.


brahamfireman
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Pto on the 856 wouldn't stop when I bought it. Previous owner said it held fine, just wouldn't stop turning.

I pulled it apart over Christmas and found most of the fraction disc wore to nothing, blue steel discs,  and brake pads wore to the metal. The back of the drum was slightly grooved from the brake pads.

I rebuilt it to the "heavy duty" specs per the RedRunRite sight. New friction and steel discs, didn't touch the orings on the drum, they looked good.

Now I haven't set the pressure yet, but when you shut it off it wants to barely turn and I can turn it by hand when the tractor is off.

What did I screw up????

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The brakes are disengaged by hydraulic pressure.  Spring pressure engages them when the hydraulic pressure to them is shut off.

Either you have collapsed brake springs, or you are bleeding hydraulic pressure to the brakes even after you disengage the pto.

Try shutting off the tractor and then turn the pto with a wrench to see how much the spring-loaded brakes are holding.

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1 hour ago, Red Tech said:

The brakes are disengaged by hydraulic pressure.  Spring pressure engages them when the hydraulic pressure to them is shut off.

Either you have collapsed brake springs, or you are bleeding hydraulic pressure to the brakes even after you disengage the pto.

Try shutting off the tractor and then turn the pto with a wrench to see how much the spring-loaded brakes are holding.

When I put it together you definitely had to press the springs down to bolt the 2 pieces together, don't see how all three could have suddenly collapsed. 

I thought about the possibility of hydraulic oil bleeding by the spool valve and backing off the springs, but I can turn the pto by hand with the tractor off. I know after assembly it was locked tight by the brake springs. 

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2 hours ago, snoshoe said:

Don't know. Several possible. First guess. Clutch drum snap ring?

That's my thought, it maybe popped out of its groove and the drum lifted, but wouldn't the big spring still push it against the brakes?

I noticed in my pto it didn't have the snap ring to stop the piston from excessive travel, but it was noted online that not all of them have it.

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This is the spring applied brake and not the newer hydraulic applied brake correct? 

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There is not a lot to go wrong here as far as the brake pistons holding the drum. As the other posters have mentioned,, if the drum retaining snap ring is not in the groove or possibly if the brake surface on the back of the drum is worn untrue you may not have enough contact area to stop the drum. If that is the case I would think if you can put up with a little while the brakes would "seat in".

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I had to reread first post. I mistakenly thought pto would barely turn when turned on. As I understand it now. My first response still stands. Comment about seal ring does not. Comment about endplay was in reference to rear bearing and it's two snap rings. Otherwise reassess groove depth and length of replacement brake pistons. With cup snap ring removed. Do the pistons push the cup past the snap ring groove?

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I have seen a light/thin snap ring in a late unit with the heavy retaining snap ring, that didn't let the brakes work very well I think. 

But I'd rate that a little unlikely, although they only get switched or wrong parts put in when they are apart.

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Didn't have much time to look at it tonite. Tractor has been off for 24 hours, with engine off I was able to turn pto shaft by hand either direction. No end play in either shaft.

Weird thing is the brake worked when it was initially put together because I tried turning shafts by hand and couldn't.

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Had a pto unit here that clutch disc's were bare metal and the metal disc's burnt as well but it was still able to turn the pto enough to run the combine but would slip under full load. That snap ring broke in two pieces when I pulled it apart. Got pretty hot I guess in there. Your snap ring may be getting weak too. Don't think it would jump out of the groove but never know. Pretty sure like was said the proper one doesn't have eyelets

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I'm fairly certain I have had early units apart that the 1000 shaft was not machined wide enough that it could use the heavy ring without eyelets. Being a 56 series I doubt it's that but there's a lot that could've happened in its life. 

Maybe those were the ones without the piston stop ring groove cut in them too I'm not sure. 

But those lighter rings seem pretty inadequate when compared to the heavier ones.

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This unit didn't have the piston stop ring in it. I also think I stretched this ring when I pulled it apart. Ring lands measure 1.78 but a new 1.75 ring is WAY to small and a 1.8125 is too big so I guess I'm going to have to call the mother ship in the morning and see if they have one.

The rounded edge is an illusion,  it's nice and square,  just stretched and didn't sit all the way down in the land.

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