8 Speed Power shift knowledge needed

[LStallbaumer2]

I have read all the conversations on this site regarding the 8 speed power shift. Lots of great knowledge out here. .Doing extensive testing before I tear into this. Here is my question – On a 68 4020 When you press in the inching pedal/clutch what does that actually do— does that cut off all oil supply to the shift valve on the right / pasenger hand side of the transmission is that ---all---- it does?? So here's the symptom that I'm trying to figure out is that 1. in park I have poor power shift pressure on the gauge on the dash goes to zero unless you got it running it 2200 rpm and will not keep front pump primed below 1500 RPM. 2. Press the inching pedal in park the power shift pressure gauge pegs out plenty of pressure. 3. And with inching pedal depressed main high pressure pump has good flow and plenty of pressure regardless of rpm. This all just started to happen and I do not believe I have cooked the clutches yet!!!. i check the screen and changed the filters and hyguard fluid. Nothing alarming in them.
Do I understand this correctly
1. The inching pedal pedal only function is to cut pressure to right hand shift valve. Nothing else
2. in park there should be no no clutches / circuits pressurized to be leaking when in park from the shift valve on right hand side of trans.
.
Then my leak has to be in shift valve orings? Could they leak so much it keeps the front pump from staying primed at Idle.

Thanks In advance for you expert information. Lynn
LYnn

 

[wore out]

I have read all the conversations on this site regarding the 8 speed power shift. Lots of great knowledge out here. .Doing extensive testing before I tear into this. Here is my question – On a 68 4020 When you press in the inching pedal/clutch what does that actually do— does that cut off all oil supply to the shift valve on the right / pasenger hand side of the transmission is that ---all---- it does?? So here's the symptom that I'm trying to figure out is that 1. in park I have poor power shift pressure on the gauge on the dash goes to zero unless you got it running it 2200 rpm and will not keep front pump primed below 1500 RPM. 2. Press the inching pedal in park the power shift pressure gauge pegs out plenty of pressure. 3. And with inching pedal depressed main high pressure pump has good flow and plenty of pressure regardless of rpm. This all just started to happen and I do not believe I have cooked the clutches yet!!!. i check the screen and changed the filters and hyguard fluid. Nothing alarming in them.
Do I understand this correctly
1. The inching pedal pedal only function is to cut pressure to right hand shift valve. Nothing else
2. in park there should be no no clutches / circuits pressurized to be leaking when in park from the shift valve on right hand side of trans.
.
Then my leak has to be in shift valve orings? Could they leak so much it keeps the front pump from staying primed at Idle.

Thanks In advance for you expert information. Lynn
LYnn

Some random thoughts...

What you are calling the "power shift pressure gauge" is actually the transmission lube pressure gauge. Transmission pump flow left over after needs are met goes to "lube", low lube pressure means the transmission pump is either low on flow or flow is being lost so there's inadequate flow left over for "lube". A "high pressure leak to sump" will bleed off flow available for lube, as well.

Dunno if your transmission pump output may be low/borderline to begin with or what all may be going on, the "B1" brake is applied in many shift positions (see chart below) and I THINK a leak at the accumulator is possible, as well, plus I suppose gasket leak somewhere in the clutch valve or shift valve area is possible, as well.

I would suggest having a factory shop manual at hand and following the troubleshooting procedures to narrow this down.

 

[WTW]

When you step on inching / clutch pedal and hydraulic function return / improve, condition indicates you shut off a transmission leak. Pretty sure clutch pedal control / shuts off oil supply to C1 and C2 clutches to release input from engine to remainder of transmission. This means leak could be in either C1 or C2 or both?? Need to monitor lube pressure gauge with transmission disconnect pulled at back of transmission / operator platform while shifting through speeds to see which clutch has better pressure and which does not referring to shift chart that was previously provided to determine which element is leaking. NOTE: 7th and 8th use both clutches. If pressure is good in speeds 1 and 2, C2 is leaking. If good in 3,4,5 and 6 C1 is leaking. Hope this helps.

 

[LStallbaumer2]

When you step on inching / clutch pedal and hydraulic function return / improve, condition indicates you shut off a transmission leak. Pretty sure clutch pedal control / shuts off oil supply to C1 and C2 clutches to release input from engine to remainder of transmission. This means leak could be in either C1 or C2 or both?? Need to monitor lube pressure gauge with transmission disconnect pulled at back of transmission / operator platform while shifting through speeds to see which clutch has better pressure and which does not referring to shift chart that was previously provided to determine which element is leaking. NOTE: 7th and 8th use both clutches. If pressure is good in speeds 1 and 2, C2 is leaking. If good in 3,4,5 and 6 C1 is leaking. Hope this helps.

The thing I don;t understand is that in park none of the clutch packs should be engaged correct. and the gauge on dash is on zero unless you rev it up. Start it up in park and it wont railse 3 point hardly at all. Press clutch in park and 3 point comes up normal and I have a loader on it and uses lots of oil and it goes up and down like normal with clutch engaged in park. l. So where is the oil going when in park and clutch let out.

 

[LStallbaumer2]

So you are saying b1 is engaged in park

 

[wore out]

So you are saying b1 is engaged in park

You can see in the chart that "B1" is applied in "neutral".

Nothing changes in the valve body as the selector is moved into "Park", the additional movement of the selector lever drops the parking pawl on the gear ahead of the differential pinion.

You could look at the chart and note a "gear" that doesn't use "B1" (2nd fwd, as an example) and shift to one of those gears and see if lube pressure comes up.

 

[LStallbaumer2]

I appreciate the info. Just trying to wrap my head around what the inching clutch does the concept before I do all the pressure test. So what I have gained from this is that the inching clutch does. If i understand it correctly it cuts pressure to c1 and c2.. ---- C1 and c2 are used in 7th and 8th I have good pressure in 7th and 8th gears only and only those two gears. and can kill motor with brakes and seems to have good flows loader works fine. 7th and 8th.

B3 is common for most other gears and is used in neutral. But oil flow to b3 is not controled by the inching pedal. So why in park / nuetral do I loose and gain pressure so dramatically with the inching clutch in neutral. That is the what I do not understand Going to put gauges on and go through the checks before I tear into it.

In 40 series manual it says to take right sided valve body off and apply compressed air to passages. I have considered just starting there.

Thanks for the info gentlemen I better get back to work.

 

[wore out]

I appreciate the info. Just trying to wrap my head around what the inching clutch does the concept before I do all the pressure test. So what I have gained from this is that the inching clutch does. If i understand it correctly it cuts pressure to c1 and c2.. ---- C1 and c2 are used in 7th and 8th I have good pressure in 7th and 8th gears only and only those two gears. and can kill motor with brakes and seems to have good flows loader works fine. 7th and 8th.

B3 is common for most other gears and is used in neutral. But oil flow to b3 is not controled by the inching pedal. So why in park / nuetral do I loose and gain pressure so dramatically with the inching clutch in neutral. That is the what I do not understand Going to put gauges on and go through the checks before I tear into it.

In 40 series manual it says to take right sided valve body off and apply compressed air to passages. I have considered just starting there.

Thanks for the info gentlemen I better get back to work.

"take right sided valve body off and apply compressed air to passages"

That MAY be what it will come down to.

 

[Scott 730]

I appreciate the info. Just trying to wrap my head around what the inching clutch does the concept before I do all the pressure test. So what I have gained from this is that the inching clutch does. If i understand it correctly it cuts pressure to c1 and c2.. ---- C1 and c2 are used in 7th and 8th I have good pressure in 7th and 8th gears only and only those two gears. and can kill motor with brakes and seems to have good flows loader works fine. 7th and 8th.

B3 is common for most other gears and is used in neutral. But oil flow to b3 is not controled by the inching pedal. So why in park / nuetral do I loose and gain pressure so dramatically with the inching clutch in neutral. That is the what I do not understand Going to put gauges on and go through the checks before I tear into it.

In 40 series manual it says to take right sided valve body off and apply compressed air to passages. I have considered just starting there.

Thanks for the info gentlemen I better get back to work.

B3 is only used in reverse.

 

[Big 86]

Does this tractor have a manual destroke screw installed at the front hydraulic pump? If so, does destroking the pump change the lube pressure?

It is highly advisable to run a full test of all transmission and hydraulic pressures before proceeding much farther. Since the lube pressure is low until the inching (aka clutch) pedal is pushed in seems to indicate C1/C2 as leaking. However, there could be another cause, such as the pedal valve and pressure regulating valve failure (some of the possibilities listed in the 30 series manual I have on hand). The JD tech manual is a must here as it goes into detail as to how and where to check pressures, and gives direction on how to proceed. You will need the manual for your 4020, as the pressure values change depending on the model of tractor even though they have the 8 speed powershift transmission.

As previously stated, the dash gauge on a 4020 is for lube pressure, the 'extra' oil in the system. I would get a quality mechanical psi gauge to verify what pressures you have when testing, as the amount of pressure drop will be helpful in finding the leak. Lube pressure is a good way to locate a problem and leak, but the system must have the correct operating pressure to function properly.

 

[Big 86]

Looked at my tech manual again for the 4430/4630 tractors, and it indicates that B2 is engaged in park. The inching pedal does not control oil to B2, but that brake is engaged in park. Manual also indicates that B1/B2 will show pressure in 7th and 8th gear, but no oil is actually going to the elements as it is stopped at the shift valve. Since 7th and 8th gears work it makes me wonder about the relationship with B1 and B2, as these two gear selections are the only times B1/B2 are not engaged.

I would think a major leak in C1/C2 should cause 7th and 8th to be problematic.

Still a check of all pressures in each clutch/brake is indicated here to verify the source of the problem.

It may not matter here, but does the PTO start and stop correctly?

 

[LStallbaumer2]

Fixed it thanks for the help It turned out to be the gasket between the cast portion of the power shift valve and the steel plate. The gasket had blew out between oil runs off of the passage that controls b1. I took the valve off the side of the trans and put air to the ports on the trans for each clutch brake etc.

They all checked out fine. Then disassembled the valve body and found the gasket failure. I recently had the body off to correct issue where the external arm on the body was loose turned out to be a spring pin that should have had one pin inside another pin but only had one pin and it had collapsed. Don't know why the gasket did not hold but this time I had the surface machined to make sure the cast body was flat and used a gasket sealer that was recommended for valve bodies. Thanks for the help!!!! Lynn

 

[wore out]

Fixed it thanks for the help It turned out to be the gasket between the cast portion of the power shift valve and the steel plate. The gasket had blew out between oil runs off of the passage that controls b1. I took the valve off the side of the trans and put air to the ports on the trans for each clutch brake etc. View attachment 75247
They all checked out fine. Then disassembled the valve body and found the gasket failure. I recently had the body off to correct issue where the external arm on the body was loose turned out to be a spring pin that should have had one pin inside another pin but only had one pin and it had collapsed. Don't know why the gasket did not hold but this time I had the surface machined to make sure the cast body was flat and used a gasket sealer that was recommended for valve bodies. Thanks for the help!!!! Lynn

GOOD JOB!

The clutch apply chart pointed to something in the "B1 circuit", I'm glad it was the valve body gasket vs. something deeper in that would require a "split" to repair!

 

[tim s]

I have chased this problem around a few times,, it always ends up being a worn transmission pump...