B20 with TPH Stuck Fully Raised

[bruceatlam]

First things first; new member here and I do belive that I ought to say "Hello" before I get to any business. Just bought a 1994 or so B20 with 027 hours on the meter. It's at least 1,027 maybe more --- it's only a three digit meter. A B20 with FEL and TPH --- no backhoe although it does have the frame for the backhoe. It doesn't look like it ever had a BH mounted. It's in reasonable shape short of some cosmetics that need attenion as time passes. Starts right up and maintains about 40 psi oil pressure at working RPM and maybe 30 at idle.

I've been browsing forums loooking for a good Kubota forum and finally landed here -- did a bunch of browsing before I purchased and have continued since.
I've learned a lot --- but not enough. Got a lot left to learn and I hope to do it here.

I've spent most of my time so far learning about it and investigating. Lots of little things that need attention but nothing big until this weekend. This weekend I ran the TPH to full raised position to check it according to the service manual and it's stuck there. Won't budge. I can hear the relief valve work with the control lever at full up position. It's not the rate valve that controls the rate at which it drops --- I've got that valve almost full left (left as you look at the knob standing by the left tire and looking at the knob under the seat) which should be the fastest rate of drop position --- but, I've had that knob in every position possible from full right, which is the lock position, to full left and no dice.

I also can not move the upper lift arms by hand -- not up -- not down.

I serched the forum and found reference to the problem in a couple of other threads but neither thread had a conclusion.

I'm starting to think that I have a fatal mechanical bind somewhere that will require many wrenches, beers and days to resolve.

Can anybody help ---

P.S. No implements mounted on the TPH and yes I stood on the lower lift arms and bounced on them and most everything else I could think of --- won't budge. Cycled the control lever up and down rapidly while standing on the lower arms --- nada.

 

[UnclePaul]

I am also a new member. I have had a B2100 for about 8 years now. I was wondering if you tried your FEL to see if the TPH is starving the hydro pump. If the FEL works like normal then its possible that it is a TPH control problem and not the hydraulic system. I hope this helps.

 

[bruceatlam]

Paul, FEL works as normal. The problem may indeed be in the control valve. If it is in the control valve then it's somehow maintaining constant pressure in that TPH piston cause it's been sitting for 48 hours now and won't budge a hair. That's an awfully well sealed system. One other thing that leads me in the "mechanical bind" direction is the fact that I can move the rate lowering valve in any direction and that should release any latent pressure on the piston and allow the hitch arms to lower --- especially with the tractor off and no pump running to supply pressure.

Maybe the pisotn is frozen in its bore somehow --- this was the first time that I had run the TPH to its full up position. Or, the rockshaft is bound up somehow --- there is a fair amount of play in the splines between the upper lift arms and the splines on the rock shaft so the whole system has seen a fair amount of use over the years.

There doesn't seem to be any direct experience with the same problem among the forum members so maybe the best possible plan is to just start taking it apart. I have to eventually find the problem. The whole thing doesn't look overly complex. A lot of bolts, banjo fittings and pipes plus I'm sure it's a tad heavy --- I could think of better things to do but I don't need it right now, so maybe I'll just start.

Thanks for the help thinking through it ----

 

[MarkV]

Not sure on the B20 but the B21 has a diverter valve to switch the hydraulics from the 3pt hitch to the outlets for the backhoe. If the diverter gets switched to the backhoe function the 3pt will not operate or operate very slowly. On the B21 this valve is a lever that is pulled up or pushed down and sets to the right of the seat. Just a thought, good luck.

MarkV

 

[bruceatlam]

I don't recall seeing that lever --- I'll look. It would be wonderful to find that as the problem. The backhoe circuit is there but the pressure hose is simply plugged in to the return hose now.

 

[tommu56]

Just a guess would the speed control for the 3 point be closed and not letting flow out.
Don't ask me how I know.

tommu

 

[bruceatlam]

I have the speed control knob full left which should be all the way open according to the manual. Left defined as standing next to the tractor and facing rearward looking at the knob under the seat. But, I've had the speed control all over the place with no impact on the problem.

You're all helping me think so keep the thoughts coming. As I study the hydraulic system and think through it, I convince myself again and again that it's a mechanical bind somewhere and not a hydraulic issue. If it were a hydraulic issue, with the engine off and that speed control knob in virtually every position and my weight on the lower arms, the hydraulic pressure has to bleed off --- unless it's possible for something to stick in that speed controla valve and keep the system perfectly sealed. It hasn't moved a hair since last Sunday.

The piston could be stuck in the bore?? The splines on the rock shaft could be bound into the splines on the arm that slips over the rock shaft to move the shaft??? That would depend on how badly the splines are worn I guess. Maybe a tap on the end of the rock shaft would dislodge it??? I haven't tried that --- I will tonight.

 

[bruceatlam]

I can close this one --- turns out that it was a hydraulic problem. I don't think that I fully understand yet, but I'll explain what happened.

Started taking it apart today. I was working to remove the TPH cylinder cap and as I was removing the bolts, the cap was separating from the cylinder. I started to adjust the rate of decent valve and as I did, the cap/cylinder separation closed and the TPH started to drop.

When this started last week, I did have the rate valve closed when I ran the TPH to it's highest position and after that the pressure relief valve actuated -- somehow that high pressure froze the rate valve. Even though I could freely move the rate valve stem left and right, for some reason it wasn't relieving the cylinder pressure. I guess that I don't exactly care that I can't fully reconstruct what happened -- it works again, it's repeatable -- all is right with the world.

Thanks to everyone for the help.

 

[MarkV]

Glad to hear it has worked out with out being a major tear down. I can't recall hearing of anyone on the forum having that problem before. Might be a good idea just to leave that valve where it is and enjoy the tractor for a while.

MarkV

 

[bruceatlam]

Glad to hear it has worked out with out being a major tear down. I can't recall hearing of anyone on the forum having that problem before. Might be a good idea just to leave that valve where it is and enjoy the tractor for a while.

MarkV

That's exactly what I plan to do ---