John Deere 400a/2020 hydraulic issues

[ProfessionalIdiot]

Good Morning All (or evening depending on where your from I suppose)

I purchased a John Deere 400a which is essentially the 2020 but instead of the 3 point hitch arrangement it has a backhoe.

They were sluggish and useless when I first bought it so I gave it a full service, cleaned the trans screen, replaced the oil etc etc. I then went and used it quite happily for a bit and after approx half a day it became sluggish and the oil got pretty toasty.

I checked the oil and it smelt burnt. As a precaution I thought I'll flush it all out, replace it and go from there. I cleaned the trans screen once again but it was pretty clear this time.

Since I've done this (and this is where it just gets silly) the air in the system renders it totally unusable. It's absolutely horrendous.

I thought well it has to be the charge pump so I've had it in bits, replaced the seals, new bearings etc and still it does it.

I've checked the output of the trans pump with the old point a hose in a bucket.and it's perfect. No air in the fluid, the right amount over a minute etc etc.
Disconnected the T piece at the accumulator on the high pressure side and Jesus H Christ. It's fluttery and spewing oil like nothing on earth.

After that looooong description my question is thus, how can the front pump draw or create such volumes of air if it is a sealed unit with a constant feed from the trans pump? It's also only putting out a very fluttery 1500psi.

Secondly do I have an internal leak somewhere to have the oil smelling burnt after approx 15 hours work? It doesnt have the rockshaft arrangement as it's a digger, so where do I start looking?

Thirdly I pulled the covers off the top of the trans and noticed a small jet of fluid from the trans pump directed forward. Is this a bearing lube setup or have the seals went?

Any light you guys can shed is massively appreciated as I'm not sure where to go next with it.

 

[Tx Jim]

Welcome to TBN
Although the models 2020 & 400 are similar there are differences especially when it has to do with hyd systems. Does your 400 have a hyd reverser? If so my guess is that is where the burnt smell originates or possibly the steering valve. I suggest to disconnect & cap oil supply to steering valve then check operation of hyd system. You're correct that trans pump lubricates the trans gears/shafts.

 

[Zebrafive]

I do not understand the small jet of fluid from the trans pump directed forward.
Can you tell where exactly it's coming from?

 

[Tx Jim]

If OP removed cover on trans case to expose trans pump wouldn't that also exposé oil galley that would supply oil to a tractor equipped with a rockshaft?

https://partscatalog.deere.com/jdrc/sidebyside/equipment/79759/referrer/navigation/pgId/171459

 

[ProfessionalIdiot]

Hi all,
The tractor insnt fitted with a hyd reverser. I can dream though lol.
There is oil that exits through the casing to what would be the gallery you mention but I currently have that filled with a piece of hose and an elbow on it so the oil is directed back into the open trans case. I think this gallery is capped off by the casing as it's unused.
The steering was capped off by my test gauge and there was no difference at all to function.
The oil jet the trans pump is spitting from is at the 12 o clock position on the trans pump itself. It shoots forward onto the rear of the bellhousing casing. Should be a picture here or here abouts.
I'm wondering if the trans pump isn't supplying the oil at enough volume and pressure to meet the demands of the front pump? Also if any of the seals have failed on the trans allowing oil to leak past at pressure hence the burning and high temps?

Thanks guys.

 

[Zebrafive]

OK, I was able to see the jet of oil in picture.
I do not know if that's by design or a casting flaw.

In your first post you said you checked the transmission pump and it was perfect.
How much flow did you get? What was the pressure?