JD401B hydraulics problems

[TMike]

I'd appreciate help with this older JD401B 3pt lift. I've read everything I could find on this forum but can't quite pinpoint the problem. The lift rises so slowly you can barely see it move. I haven't put guages on the transmission pump but the main pump seems good. I adjusted it up from 2100 psi to 2250 and it seems steady. I've checked pressure at the pump, at the pressure control valve and at the port on the right side of the rockshaft. The oil at the rockshaft port had air in it...looked foamy. Not sure if it's a problem, but may be a clue.
I've replaced the trans filter and screen and cleaned the main pump screen. I repaired a broken pin in the oil filter relief valve, which got the steering, brakes, and pto going. The brakes work OK but require pumping.
Right now, I have the rockshaft off and mostly disassembled. The main piston bore looks unscarred and I've ordered a ring/gasket. Two things I'm guessing could still be the culprit now are the control valves in the rockshaft or maybe the pressure control valve I've seen referred to as priority valve. I havent found much info on either of these ...at least not yet. Any suggestions on where to go from here or if I missed anything obvious?? Thanks

 

[TMike]

Update:
Replaced Orings in 3pt control valves and adjusted linkage. No improvement. I did notice, looking through the hyd fluid filler cap, oil spraying but think it may be lube for the trans gears? Next, I think I'll check adjustment of the L/D. Guess I'll be welding a socket and extension.

I mentioned the priority valve previously but DO have good pressure at the rockshaft, so think it may be ok.

Running out of things to check........

 

[TMike]

May be on to something now. Just discovered the flow valve in the rockshaft cover is stuck. Crossing my fingers cleaning it fixes my problem.....

 

[Tx Jim]

May I ask where exactly is this flow control valve located that you're referring to in rockshaft housing as I can't remember a flow control valve located in that location other than rate of drop screw?? By chance are you referring to the pressure control valve located close to the hyd filter cannister? FYI L/D screw was intended to ONLY be adjusted while performing ALL 3 pt linkage adjustments outlined in a JD utility tractor technical manual.

 

[TMike]

The valve is identified in my TM 1091 manual section 50 50-7 Figure 6 as Flow Control Valve. It's just in front of the L/D lever assembly in the rockshaft housing behind a plug. Freeing it up did get the lift working but it's still slower than it should be. I think my problem now may be the pressure control valve. I did make the other adjustments IAW the manual but this was my first time.

 

[Tx Jim]

Thanks for your explanation. I've never experienced any problems with the valve you referred to

 

[TMike]

Unless I missed it, there's precious little information about it in the TM. It's a spool, a spring and a washer. It could still be part of my problem. Freeing it up definitely helped the 3pt but its still too slow. Any ideas?

 

[Tx Jim]

Set hyd stand-by pressure to 2350 psi

 

[TMike]

Thanks Tx Jim. Will try that next.

 

[Tx Jim]

You're welcome

 

[TMike]

Well, I increased pressure to 2350 today. I think it helped a little, but something is still not quite right. The 3pt lift is just slower to rise than it should be. Scratching my head on this thing. Any other suggestions?

 

[TMike]

The flow control valve may still have a problem. I removed a valve (spool?), a spring and a small flat washer. Then, proceeded to clean out the bored area. There are two other passageways that intersect with the valve bore, I think. One has a steel ball at one end in the rockshaft housing. I have not removed it---not sure if it can even be easily removed for cleaning? If anyone can elaborate on this flow control valve and whether I should remove the steel ball, please let me know.
Regards
TMike

 

[Tx Jim]

Some passageway's have a ball driven in the hole to block the passageway.

 

[TMike]

Guess mine is one of them, TX Jim. Good to know--Thanks.

 

[Jim.ME]

Guess mine is one of them, TX Jim. Good to know--Thanks.

During manufacturing machining sometimes, a passage has to be drilled to join some internal passages and has to be drilled from an external point where it would be a leak if not plugged. Driving/pressing a ball in the hole is just a way to plug the hole that should never be opened as it was only needed to make the component, and it can be done without threading for a plug.

 

[Tx Jim]

Guess mine is one of them, TX Jim. Good to know--Thanks.

You're welcome

 

[TMike]

More expert knowledge from the pros. Thanks Jim.ME. I'm trying to rule out every possible point of failure. Since I have pressure and the 3pt does lift, seems to me there's only a few things it could be. One thing bugging me. The lift lever quadrant assembly has broken and been welded back. It looks to me like it may be between 5 and 10 degrees out of position (leaning about that much too far forward). I can cut, move and reweld it but I'm not confident that's the cause of my problem. Thoughts?

 

[Tx Jim]

I think location control handle was welded to 3pt operating shaft could limit height 3 pt raises or lowers but won't have much affect if 3pt will operate.

 

[TMike]

That's what I was thinking too, TxJim. It just acts like high pressure flow is restricted to that cylinder somehow and I was thinking maybe the precise position of the lever and linkage may have had more to do with it than I realized-- to the point that perhaps it was beyond correct adjustment.

 

[TMike]

Update:
I've replaced seals/gaskets/rings in the 3pt lift cylinder and valve assemblies. I've increased standby pump pressure by 100 psi. I freed up a stuck flow control valve in the rockshaft housing (this was preventing the lift from operating). I've readjusted the L/D adjustment screw, lift linkage and lever by the book. I've drained the hydraulic fluid and replaced with J20 compatible fluid. I had gone with a less expensive alternative.

Honestly I'm pretty happy the lift is working as good as it is, so everything is back together and I doubt I'll work on it much more unless I learn something I think will make significant improvement. The problem is still that the lift doesn't rise as quickly as I think it should. Again, it's satisfactory, I suppose...just not ideal.

At this point, the only other thing I can think of that might be restricting the lift speed is the pressure control valve/priority valve ....and I have my doubts about that simply because at last check at the rockshaft portal (right upstream of the flow control valve), I had plenty of pressure. I didn't pick up on this at first, but I think the TM indicates two different pressure control valve diagrams based on tractor serial number. I recall thinking mine may not be correct. When I have a chance, I'll check that.