990 pto issues

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simondavidmartin
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Location: West yorkshire

990 pto issues

Post by simondavidmartin » Thu Dec 17, 2015 6:47 pm

I am having problems engaging the pto on my 990 implematic, when i depress the clutch and engage the pto lever it grinds like hell and refuses to go it. this is the first time i have used it, and it may not have been used for quite some time.

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ollek
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RE: 990 pto issues

Post by ollek » Thu Dec 17, 2015 7:08 pm

It is possible that the pto clutch plate is sticking to the flywheel and/or the intermediate plate. Connect a pto driven implement that needs much power to the pto. Then start the tractor and press the clutch pedal fully down whilst the implement is working. I take that you understand that the pto clutch disengages when the clutch pedal is pushed fully down. The last bit of pedal travel is quite heavy, step on the pedal.

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simondavidmartin
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RE: 990 pto issues

Post by simondavidmartin » Thu Dec 17, 2015 7:12 pm

I cannot engage the pto at all when the tractor is running with an implement on, it just grinds. if there is no implement on and the tractor is running i can engage it but it grinds a little.

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db2d
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RE: 990 pto issues

Post by db2d » Thu Dec 17, 2015 8:28 pm

If the suggestions by Ollek do not work the probable reason is the transmission plate is worn down to the stage where it needs renewing. Adjusting the clutch internally is a ' quick fix ' that eventually leads to disintegration of the transmission plate that entails a costly repair

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testbed
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RE: 990 pto issues

Post by testbed » Thu Dec 17, 2015 9:31 pm

DO you realise that to try and free the stuck clutch you need to engage the pto drive with the engine stopped (which may require the pto shaft to be turned very slightly if it is out of mesh) and the pto shaft already connected to an implement which is raised up off the ground so there is as little power required to start the engine as possible. then once running with the foot hard on the clutch at all times vary the revs and require the implement to work as hard as possible in the hope the clutch will release. Often they release as the flywheel warms up to working temp just about the time you are about to give up!

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erkki
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RE: 990 pto issues

Post by erkki » Fri Dec 18, 2015 6:11 am

Testbed's trick is worth trying.

The crank bearings are not designed to run constantly with clutch pedal pressed down, so when trying release by driving, let the pedal up every now and then to ensure axial bearing cooling and lubrication.

If the pto clutch plate has stuck to the flywheel, it is worth trying also to tie the pedal down for a couple of days and make a constant torque to the PTO shaft with PTO gear in 1000 rpm. Soaking the whole assembly by diesel fuel and spray gun may also do the. Diesel will evaporate off when the tractor is taken in use.

W.B.R erkki

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DB780
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Post by DB780 » Fri Dec 18, 2015 8:47 am

It may be the PTO clutch just needs adjusting internally. To do that remove the inspection cover under the clutch housing. In there on the clutch assembly, evenly spaced between the release levers you will see 3 nuts with allen socket screws in them. You need to slacken the nut and screw the screw in until it contacts the metal plate then back off 1 1/2 turns the tighten the nut. Repeat this on all 3 adjusters and you should be fixed.

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ollek
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Post by ollek » Fri Dec 18, 2015 12:05 pm

Please be aware of, that the adjustment of the 3 internal Allen screws can result in costly repairs. The reason is that wearing of the transmission plate will lead to that the pto clutch does not release and this will happen when the transmission plate has worn to the extent that it has to be changed. The problem with the disengagement is in this case a warning that the rivets in the transmission clutch plate will soon start to get in contact with the pressure plate. Adjusting the inner Allen screws will correct the problem with the pto clutch but the transmission clutch plate have to be change as soon as possible. Please see earlier posting from db2d. This same subject has been on this forum a couple of times and there is always some who recommends the internal adjustment. I wold definitely no recommend this 'quick fix'. And one more thing, if you do go for the internal adjustment, then backing off the screws one and a half turn is wrong, they have to be backed off three quarter of a turn.

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DB780
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Post by DB780 » Fri Dec 18, 2015 1:56 pm

ollek wrote:Please be aware of, that the adjustment of the 3 internal Allen screws can result in costly repairs. The reason is that wearing of the transmission plate will lead to that the pto clutch does not release and this will happen when the transmission plate has worn to the extent that it has to be changed. The problem with the disengagement is in this case a warning that the rivets in the transmission clutch plate will soon start to get in contact with the pressure plate. Adjusting the inner Allen screws will correct the problem with the pto clutch but the transmission clutch plate have to be change as soon as possible. Please see earlier posting from db2d. This same subject has been on this forum a couple of times and there is always some who recommends the internal adjustment. I wold definitely no recommend this 'quick fix'. And one more thing, if you do go for the internal adjustment, then backing off the screws one and a half turn is wrong, they have to be backed off three quarter of a turn.
I recommend this adjustment because I don't believe you statement to be correct. I and many other mechanics have adjusted the PTO in this way for many years. As the transmission plate wears no matter how much it effects the PTO adjustment and adjusting the PTO adjusters compensates for this. So you are trying to tell everyone that as soon as the PTO fails to clear the transmission plate is worn out? I

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ollek
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Post by ollek » Fri Dec 18, 2015 2:18 pm

What I am saying is that if the internal Allen screws need adjusting in order to get the pto clutch to disengage, then the transmission clutch plate is worn almost down to the rivets. This is the technical fact and others can be of the opinion they want. But be aware of the risks taken if the Allen screws are adjusted in an old tractor. No one can ever change my opinion in this subject as it is based on technical and engineering facts, and not on any ones "opinions". And I do know that many fitters adjust the Allen screws, but without really realising what they are doing.

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db2d
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Post by db2d » Fri Dec 18, 2015 7:35 pm

The thickness of a new transmission plate is 0.350 inches and the correct gap setting for the PTO adjusters is 0.070 inches during installation and the free play on the clutch pedal at one to one and a half inches. As the transmission plate wears the thrust mechanism moves out towards the gearbox and the free play on the clutch pedal decreases and the gap on the PTO adjusters increases.
When the transmission plate has worn down and the gap on the PTO adjusters has increased to the point where the PTO does not disengage this indicates that the transmission plate has worn down to the rivets or there abouts.
If the PTO adjuster gap is reset at this time the PTO will then disengage as normal but the transmission plate will then continue to wear down through the rivets until it disintegrates usually damaging both pressure plates ( costly )

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DB780
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Post by DB780 » Fri Dec 18, 2015 8:55 pm

db2d wrote:The thickness of a new transmission plate is 0.350 inches and the correct gap setting for the PTO adjusters is 0.070 inches during installation and the free play on the clutch pedal at one to one and a half inches. As the transmission plate wears the thrust mechanism moves out towards the gearbox and the free play on the clutch pedal decreases and the gap on the PTO adjusters increases.
When the transmission plate has worn down and the gap on the PTO adjusters has increased to the point where the PTO does not disengage this indicates that the transmission plate has worn down to the rivets or there abouts.
If the PTO adjuster gap is reset at this time the PTO will then disengage as normal but the transmission plate will then continue to wear down through the rivets until it disintegrates usually damaging both pressure plates ( costly )
This sounds a little theoretical to me but how do you know when the PTO needs adjusting, it could be before the transmission plate half worn or less towards the rivets. I agree if the adjusting screws are disappearing into the locknuts it's time to be changing the transmission plate but not as soon as it needs adjusting especially if there is still plenty of adjustment on the pedal.

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db2d
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Post by db2d » Fri Dec 18, 2015 10:51 pm

The wear on the transmission plate and the increase in the PTO adjuster gap are mechanicly linked. As the transmission pressure plate moves forward due to wear on the drive plate the PTO adjuster gap has to increase It is a built in feature and has been the same from the DB 900 days

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ollek
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Post by ollek » Sat Dec 19, 2015 5:48 am

The Allen screws shall be adjusted only during a clutch repair when a new transmission clutch plate is fitted. Adjusting the screws in the way DB780 is suggesting will make it possible for the driver to continue using the pto until the transmission clutch plate disintegrate without any further warnings. I strongly recommend to change the transmission clutch plate as soon as possible if adjusting the Allen screws helps in disengaging the pto clutch. This is not theoretical at all, it is a mechanical fact.

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DB780
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Post by DB780 » Sat Dec 19, 2015 9:31 am

ollek wrote:The Allen screws shall be adjusted only during a clutch repair when a new transmission clutch plate is fitted. Adjusting the screws in the way DB780 is suggesting will make it possible for the driver to continue using the pto until the transmission clutch plate disintegrate without any further warnings. I strongly recommend to change the transmission clutch plate as soon as possible if adjusting the Allen screws helps in disengaging the pto clutch. This is not theoretical at all, it is a mechanical fact.
So after a period of use you when the PTO clutch needs adjusting you say a new transmission plate needs fitting, what 'theoretical' twaddle. Where in any service manual does it say this?

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