10/20 Series Transmission Check Valve Modification

[Glen D Anderson]

With respect to the attached OEM service information for the transmission check valve modification designed to solve the lack of hyd. pressure after initial start up, I have some findings to share.



Last year we performed this mod. on our 64' 3020. After installing the check valve in the elbow & admiring the finished product it hit me like a facepalm "I just installed a 3/8" check valve in a 3/4" fitting!"

Knowing that the circuit could potentially see the max. output of the pump which could be close to 20 GPM on paper I started to get concerned so I installed a pressure gauge in the return circuit & installed a jumper hose in one of the SCV outlets to test.

With the engine running at at high idle, hyd. oil ambient / shop temp., SCV cycled with a loop hose on the breakaway, back pressure started at 125 PSI. I continued to run the test for 15 - 20 minutes to see if the back pressure would drop as the oil heated up & was surprised to see the back pressure take an immediate 25 PSI jump up to 150 PSI out of the blue for no apparent reason.

I wasn't happy with what I saw so I removed the fitting so I could remove the check valve to re-test & what I found shocked me. The check valve cage had been pushed off the body & was sitting in the bottom of the fitting along with the spring & check ball. When I installed the check valve I had only drilled the fitting deep enough to accommodate the threads of the check valve thinking that it would help hold the cage on the valve. That apparently didn't work. LOL

Anyway I removed the check valve completely & re-tested again this time the back pressure had dropped to just under 60 PSI.


Now I realize that in the real world 95% of the applications out there will not have the tractor operating at that high of a flow rate so the restriction of the 3/8" check valve may be a moot point. However, if you happen to be in that 5% that uses a loop hose to pre-heat your hyd. system in the winter or perhaps you pull something like a Valmar air-seeder you'll want to take note.


FWIW, if I have to deal with this kind of issue in the future I think I will be installing a 3/4" check valve at the outlet fitting & shortening & re-flaring the steel line to accommodate. It'll be more work & $$$ but will result in a better fix IMO.


Food for thought....


JD Service Literature

Fitting with check valve installed

Engine speed during test

Back pressure with check valve(possibly fallen apart)

Back pressure without check valve

Possible location for external check valve

 

[ET]

The check valve looks identical to the
one used in dubuque tractors. The cage,
ball and spring is usually gone when I've
split those tractors.

 

[WTW]

The Dubuque application for this check ball was only used on tractors with no reverser or two speed option. Just the seat was used on all tractors with this option. So most would not have the ball and spring. I have seen where some had them added but was not there originally. Won't hurt anything if added but, not needed in these applications / options. DW

 

[buickanddeere]

Excellent research and analysis .

 

[ET]

The 1020's and 301's I maintained had niether a reverser or a hi/lo.

 

[WTW]

That would be correct they both would of had the check ball in the pump charge line. DW

 

[SVcummins]

Well I guess Ill drain the oil again and pull mine out . Thought
I found a good idea guess not Ill just have to start the tractor
and let it sit a few minutes which is a good idea anyway

 

[Glen D Anderson]

Hold on! LOL

I'm not advocating that everyone remove these valves in favor of something else.

Just be aware that they will cause additional back pressure to the return circuit, the result of which I cannot attest.

One thing I had thought about doing if I was going to keep the check valve would be to install a bolt, probably 5/16 NF, in the elbow on the opposite side of the check valve. It would be cut to length so that it would provide a stop for the cage to rest on & prevent it from popping off. Obviously the fitting would need to be drilled & tapped and the head of the bolt sealed with a copper washer.

FWIW

(quoted from post at 20:52:51 04/19/21) Well I guess Ill drain the oil again and pull mine out . Thought
I found a good idea guess not Ill just have to start the tractor
and let it sit a few minutes which is a good idea anyway

 

[fdt860]

Great information.
To get real fitting backpressure, I think that it is safer to mesure before and after the fitting, but I may be wrong.

I agree with you that 3/8 seems too small for feeding the pump. Deere never stopped increasing the feed line pipes for the 10,20,30, 40, 50 series

 

[Glen D Anderson]

Measuring before & after the fitting would show the pressure drop without having to remove the check valve. Plus the gauge after the fitting would show how much back pressure was coming from the excess oil that was flowing through the cooler / return plumbing.

Measuring the way I did it just meant that I had to take a reading before I removed the check valve & then again after it was removed.

So, it had a 65 PSI pressure drop across the the check valve to start with & then 90 PSI after the cage blew off & the parts piled up in the fitting.

To get real fitting backpressure, I think that it is safer to mesure before and after the fitting, but I may be wrong.