pto clutch pressure readings

   #1  

jonsstihl

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Hey guys. Just a little info I would like to share about an interesting observation I made on my PTO clutch pressure system.

been chasing a PTO clutch problem around for a few years now and trying to avoid splitting the tractor to repair.

My point is to be careful when checking the pressure. I was surprised to find the pressure varied anywhere from 280psi to 370 psi depending on idle or rated rpm and whether the oil was hot or cold.

manual says to test at rated rpm and with oil between 40 and 60 degrees celsius. spec is 362psi to 413 psi for HST models.

oil at 10 degrees at idle I was getting around 280 psi
oil at 40 degrees at idle was getting 300PSI
oil 40 deg PTO RPM was getting 320 PSI
and oil at 40 deg PTO rpm actually using the PTO (with a wood chipper) got 370 PSI

what really surprised me was how much of a difference the temperature made because I wasn't expecting that much of a difference with only 30 degrees difference.
as a reference
room temp is approx 20 deg C water freezes at 0 deg C and water boils at 100 deg C

ran the tractor for a couple of hours running a hydraulic splitter and the oil never got much above 40 deg C compared to engine oil at 65 at the filter.

temps were taken with a laser thermometer.

there is a check valve (ball and spring) in the elbow at the pto clutch solenoid valve that can cause trouble. it has been removed in newer models and can also be removed from older models.

also another problem area is the spool in the pressure reducing valve sometimes sticks so it was suggested that I remove it to confirm free movement and polish lightly.

I removed the spool last night and everything was clean. had to gently pull with needle nose pliers to get the spool out but no visible damage or debris was found. didn't get to test the pressures after the spool cleaning but will test again.
 
  
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jonsstihl

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here is a link to a better description of the problem.

what I have also learned in the mean time is that the PTO clutch circuit is powered from the power steering side of the pump not the main system side.
 
  
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jonsstihl

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cleared the drive way this weekend with the blower and after about an hour of running it engine oil temp was 48 deg C and hydro oil was at 32deg C so about like a hot summer day. not death valley hot but still hot for around here. Not quite up to the 40 deg minimum the shop manual calls for and the PTO pressure was 340 PSI
 
   #4  

mcfarmall

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Interesting findings. Thanks for posting all of your data! I'm sure that it will be of help to someone along the way. L4740 correct?
 
  
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jonsstihl

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Yes correct, an L4740 2012
i'm not to worried for now because it is within range when at the right temp and tractor is still functional unless mowing at hot ambient temps for a long time. I will have to see about getting a pressure gauge teed into the power steering circuit to see if that is within spec. I couldn't find anything in the manual about adjusting the pressure other than replacing the steering controller if not within spec.
 
  
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#6  
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jonsstihl

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it really isn't hard to get a gauge on the pto clutch circuit it is an 1/8 npt plug. If it saves you the pto clutch issues I am having you will be glad you took the time to do it.

the point of this thread was to let guys know that they should check their pressures and that the oil temps affect the pressure more than I thought they would.
 
   #7  

MHarryE

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I was surprised to see your lower pressure reading when cold than when a bit warmer. Then, having owned a Grand L 40 (L5740) I remembered suction filters and what they do with cold oil. At Caterpillar, my products mostly had a strainer at the inlet of a gear pump supplying charge and steering oil. From the pump the charge flow when through a dual pressure filter before charging the hydro. This was to insure the hydros (we had 3 hydros, one for front axle, one for rear axle, and one for implement) never cavitated due to low pressure. Kubota has the suction filter up front which creates more restriction at the gear pump inlet and is a reason for SUDT-2 and its cold flow properties. We had one suction filter system at my Cat division, a product from a company we purchased. In our Minnesota plant, we used a fork lift to carry the 15 ton machines due to be shipped the next day inside overnight to warm the oil so they could be driven on the truck. Our filtration after the charge pump was not always a great thing because if a person revved the engine to high idle when really cold, they could blow out the charge filters. My M7 with KVT has its hydrostatic motors in the transmission that are very touchy. Warm up procedure is idle for 5 minutes at temps over freezing, 15 minutes for 14 to 32 degrees, 25 minutes for -4 to 14, and more than 30 minutes for temperatures below -4. If you neglect to warm up, the tractor will refuse to operate. The ranges I listed - it will not allow you to move for 3, 5 or 7 minutes so giving some warm up is a must. When I start on a cold morning (we have had temperatures to 0 this week, -10 forecast for Monday night) I have warning alerts and continuous beeps. Time to go inside and have another cup of coffee. The M7 does not have the luxury of being able to use SUDT-2. It has a special UDT-HD oil and at $72,000 for a reman transmission, I am not going to try anything different. The WSM that I still have for the L5740 shows a direct relief in the PTO system so the greater the flow going over relief, the higher the poppet must lift against spring pressure to create a wider flow path and the higher the pressure. So a PTO clutch will be pressure sensitive for it's torque capability but PTO is a set engine speed and therefore closely controlled at normal operating temp.
 
  
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jonsstihl

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thanks for the info. I am running sudt 2 in it. your 6060 should be very similar in terms of pto clutch operation. the oil for the pto clutch system is taken from the power steering circuit and reduced by a presure reducing valve. maybe that is why pressures are lower when cold. I'm used to seeing high pressures when cold (think oil pressure in an engine)

I would have thought the bypass valves would open before the filters blew out.
 
   #9  

5030

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One thing to always keep in mind and that is Kubota's have notoriously weak clutch brakes. When running any implement that don't have a built in over running clutch, I advise adding one to the pto stub. Will save you a lot of grief down the road because the only way to access the hydraulic clutch pack is by splitting the tractor. If you remove the pto shaft carrier in the back, you can see the pack but no way can you reach it. Strictly 'unobtainum' unless you split the unit.
 
 
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