JD 855 Inop PTO's - Appears to Be Hydraulic Related

[Dan B]

JD 855 Inop PTO's - Need Help, Savannah Dan
Hello Everyone, my name is Dan & we live in Savannah, GA. I have a 1989 JD 855, Hydrostatic Drive Compact Tractor, with 60" mowing deck and 875 hr. It has been has been a pretty good tractor for us for approx 20 yr. It has had some problems over the years, but nothing I have not been able to sort out till now. I am now challenged with the PTO's Mid and Back inop. We can not cut grass (not good in Savannah in the Summer). I have gone through all of the simple electric checks, Seat switch and the time delay control module check, but no luck. I can see the PTO engagement lever on the left side of the Rear housing moving to engage (roll pin is good on shaft), but neither PTO will work. Suspect some type of hydraulic mechanical problem in rear transmission drive unit . . ? ? Forward & Reverse Hydrostaic Drive seem normal, but have noticed slight lack of hydraulic power steering boost (extra force required to turn frt wheels when stopped - higher Engine RPM seems to help). {I do have a JD 855 Parts Catalog and noticed the Power steering valve hyd return line goes to the PTO input cover ? } Last time I used the Tractor, I noticed the PTO did not want to engage - eventually sort of engaged, but I suspected not quite fully. It was 100 degrees outside but there seemed to be a lot of hotter than normal airdraft coming up from under the tractor and the rear Hyd Transmission had a little different pitch / whine than normal (Transmission sounds normal now - but no PTO's). After cutting 2 acres, I parked the Tractor. Couple days later I checked over all fluids and everything checked good, except no PTO's ? I now have a JD 855 Technical Manual on order, should be here in about 5 days 7/20/12, but I would really appreciate any help from someone who may have had a similiar or same proplem. I am a licensed Aircraft Mechanic and work with a lot of Aircraft & cars, but I have always been a little hesitant to go into the hydrostatic rearend of the 855. Noting that it is challenge to find reasonable Tractor Dealership repairs on these type of problems, I hoping someone can give me some general guidance on where to look and start on this problem. As a quick note there is no burnt smell to the Hydraulic fluid. Fluid & Filter were changed at approx 500 hr. As I am not looking forward to cutting 2 acres with a Lawnmower for long, PLEASE HELP FAST ! Thanks Everyone, Savannah Dan 7/16/12

 

[jd110]

I assume you have shifted mid and rear lever and that lever feels normal. If you grab pto shaft by hand, does it turn freely or is it tight? I am attaching parts diagram of the pto valve and lever. I asume lever #14 is what you are seeing move when you engage pto. It turns lever #29 and moves valve #23. That valve then sends oil pressure to modulating valve assembly parts #1 thru 12. I am suspecting this modulating valve may be your problem. It could be seized in housing, have broken springs or have blown orings.

 

[v8only]

I know you said you checked all your electrical but since you are waiting on your manual read over my thread here: http://www.tractorbynet.com/forums/...249542-pto-stopped-working-seat-switch-2.html

There are also some pictures with how to trouble shoot the PTO system electrically. As you will ready it took me a while to find the faulty TDC module. Also make sure the magnet is engaging.

 

[Dan B]

Hi JD110 Thanks for your inputs. Yes, Not sure if this correct, but Mid / Mid Rear & Rear PTO's turn freely when selected out of Gear. In other words, if the PTO lever is set to rear, the Mid PTO will turn freely and conversly if you select Mid only the rear PTO rotates freely. {Should they be turn freely when in gear ?} When PTO's selected in Gear, I need a very large wrench to turn - (very difficult). I did take the back PTO Spool #28 switch cover off and and was able to see the PTO modulating valve Spool move forward & aft when I moved #14 PTO engagement lever, There does not seem to be any binding in the movement of the the PTO modulating valve Spool. The related modulating spool back spring appeared to be OK from what I could see of it.
I do have the 855 Parts Catalog and looking at page 50-20, illustration MP3859, is there a possibility that the actual PTO Clutch (top of the rear end unit) is bound up not moving to engage the PTO Clutch ? ? Or ref illustration MP4712, could #20 / #21 PTO Shift Fork / Shaft be binding or jammed ? ? I really appreciate your help and I am trying to do take the rear unit apart as minimally as possible, but will do what ever you suggest that makes the most sense. I will take the Parts Catalog to work with me tomorrow, if you want to call me. My number is 912 965 7123 or direct e-mail is Dan.bradl@gulfstream.com Again Thank You very much for your inputs and guidance. Savannah Dan 7/17/12

 

[Dan B]

Hi JD 755 Thanks for your input and attached thread. I did go through that same check of the TDC module by jumpering the tractor side of the TDC harness (Yellow to Blue). but there was no change. I also took the TDC apart and the coil / points looked good. Also the magnet connection is good and the PTO indication light on the dash lights up and the PTO engagement lever, left rear side of the rear drive unit movesforward, but the PTO is not engaging, which is why I am suspecting the issue is internal to the rear end Drive / PTO mechanical unit. Savannah Dan 7/17/12

 

[Mechanos]

Only other things I can think of are the delay valve, the PTO clutch pack and the PTO brake pack. When pressurized oil is applied to the circuit the delay valve delays the engagement of the PTO. Once it's done its thing, pressurized oil is supplied to the clutch pack and the brake pack. A spring loaded piston holds the brake on... the pressurized oil moves the piston removing pressure from the brake pack releasing the brake. At the same time, pressurized oil engages the clutch pack piston putting pressure on the clutch disks which engages the clutch pack. If the seals on the clutch shaft are allowing oil to leak by, the PTO clutch may not be receiving enough pressure to engage the clutch pack. If the seals aon the brake piston are leaking, there might not be enough pressure available to release the brake.

 

[Dan B]

Only other things I can think of are the delay valve, the PTO clutch pack and the PTO brake pack. When pressurized oil is applied to the circuit the delay valve delays the engagement of the PTO. Once it's done its thing, pressurized oil is supplied to the clutch pack and the brake pack. A spring loaded piston holds the brake on... the pressurized oil moves the piston removing pressure from the brake pack releasing the brake. At the same time, pressurized oil engages the clutch pack piston putting pressure on the clutch disks which engages the clutch pack. If the seals on the clutch shaft are allowing oil to leak by, the PTO clutch may not be receiving enough pressure to engage the clutch pack. If the seals aon the brake piston are leaking, there might not be enough pressure available to release the brake.

7/22/12 Thank You Mechanos for your inputs. I received my JD 855 Shop Manual on Thursday and went through all the related info and illustrations regarding the Hydraulic PTO system on the 855. I rechecked the PTO electrical switches one last time to confirm they were engaging properly and pulling the PTO engagement lever, left side of the rear differential. I also did a PTO Clutch pressure check (Port, upper aft left corner of the rear diff, right above the PTO Clutch & Brake Control valves). There was supposed to be 30 -120 psi at 3450 rpm with the PTO engaged, but since the PTO clutch will not engage there was 0 pressure. I then took off the PTO Valve side cover (left side rear differential) and removed both the Clutch and Brake Control valves. I disassembled both spools and Springs / o-ring seals looked OK. I then removed the Hydraulic Pump, PTO Inertia Brake cover, PTO inertia Brake, springs & piston. PTO Brake Clutch disc & stators measured / inspected OK. I then drained the balance of HYD fluid and inspected the metal screen Return filter at the bottom of the rear differential. With a little over 800 hours on the tractor there was very little dirt and or metal shavings inside bottom of rear differential cavity. I am now at a loss as to what to disassemble / inspect next. It is also very frustating in that I have not found anything that appears to be abnormal. Please also remember that the Tractor hydrostatic drive and rear lift systems are working normal. The steering however does appear to have a moderate resistance at lower rpm (approx 1600 rpm) which it never seemed to have before. Noting that the PTO hydraulic feed pressure comes from the steering return pressure, is there something I should be checking there or with the flow divider valve, which output hydraulic pressure feeds the steering system. Any help / suggestions are very much appreciated. Thanks, Savannah Dan 7/22/12 10:23 PM

 

[Zebrafive]

Probably not a help, but on my JD2030 its hydraulic PTO quit and when engaged the three point hitch would not work. It turned out to be an internal steel line from the PTO valve to the PTO clutch had broke and when engaged was just dumping hydraulic oil back to sump. I had to split the tractor to replace the line.

Since you have zero pressure at the PTO test port, you need to determine how pressure gets to the PTO valve then how it gets to the PTO clucth. Having the parts catalog and service manual you should be able to track it down.

 

[David VanName]

There is a pto safety interlock switch under the seat to automatically turn off the pto should you dismount tractor while pto is engaged. This switch has a manual bypass position so you can operate a 3 point hitch post hole auger while standing beside the tractor. Something to check.

 

[Ed J]

Dan,
Did you ever find this PTO problem with your 855? I am having the very same thing on my 655. tried your email but it bounced..
r
Ed