8670

[cushman]

I have a friend who brought me an 8670 to try to solve a transmission problem.Starting in 1st upshifting is fine until the 9th-10th shift,at which time it will stall the engine,unless it is clutched,at which time it will go up to 16th OK.Then downshifting it almost stalls with the 8th-7th shift.I have had the CCM to Farmtronics twice,used a known good CCM once,and have found that with the 9th 10th shift the F1 clutch continues to have current to it instead of dropping out when the F2 clutch gets powered up,thus stalling the engine.On the 8th-7th shift the F2 clutch holds current almost long enough to stall the engine.The service manual shows the wiring diagram,but does not tell why the current does not release the clutches when they should.Does anyone know if the instrument panel could be involved?

 

[Larry NCKS]

This is off the top of my head. Modulator valves????
Maybe Bern will chime in here????

 

[Bern]

First thing I'd do is a clutch calibration if you haven't already. Instructions for doing so are in the owner's manual. Make sure the oil is hot.

I don't know how you're determining that one clutch is not releasing soon enough, but I suspect you're overthinking that particular angle. If you're looking at both F1 and F2 current ramps with a scope, you likely will see both engaged at the same time for a brief moment. Since it takes time for a clutch to actually "bite" once it's engaged by the modulator valve, you don't want the off-going clutch dropping too soon or else you end up with a huge hesitation, which is not good under a heavy load.

Understand also that the 9-10 upshift and the 8-7 downshifts will always be the roughest on that particular machine. Having said that, it shouldn't stall the engine while doing it.

If it was in my shop, I'd be comparing actual clutch pressures with the current signal while doing a calibration, for both F1 and F2 clutches. I'm guessing one or both are sticking and not modulating like they're supposed to.

 

[Sean in PA]

I don't know if that tractor has a seat safety switch, but I was having a similar problem on my Kubota with the engine dying whenever I was trying to backup a steep hill. I thought something in the transmission was somehow dragging the engine down and killing it when I was stressing it in reverse. Turned out that the seat safety switch had shifted in its mount and when I was starting out in reverse on a steep hill my weight shifted and the switch triggered. So if that tractor has a seat safety switch and those two shift points cause the tractor to lurch more than the others, the operators weight might be shifting on the seat causing the switch to trigger.

 

[cushman]

I see that F1 is held in by still getting current to the solenoid, while F2 is also getting current.I cannot get the instrument panel to get me the calibration menu,so I cannot calibrate the clutches.

 

[Bern]

I have to assume you're using a scope to see both F1 and F2 energized at the same time. As I said below, it's normal to see that for a split second. As for the instrument panel, I seriously doubt it has anything to do with the shifting you describe.

The rest of my advice below still stands.

 

[cushman]

I should have also mentioned the F1 voltage stays at 6.2 until the engine has stopped,at which time it drops to 0.

 

[Bern]

Sounds like a wiring issue to me. Time to get a wiring diagram out and start with some continuity testing of the harness.