Deere 4400 low charge pressure, won't move

[rScotty]

Sounds like we have the same suspicions. Where does the charge pressure enter the transmission? I am still not clear on that. If using air pressure for a diagnostic tool - i think that is a good idea, btw - because then he could measure at the test points to see if the air pressure is the same there as incoming.... That would help diagnose for internal leakage. So how to do that?

I wonder if he can remove the spin-on filter and use that connection as a port? There are a number of filter port rmounting adapters available for moving the filter outboard and/or putting on old school bypass filtration. Would using one of those kits provide an air injection port?

rScotty

 

[AndrewInOz]

Maybe already mentioned, but from the dotted pilot line, I read that "charge relief" valve as setting the upstream pressure ( for PS & aux ) so a downstream pressure of 30psi is not necessarily bad. This is simply the back pressure from charging the pump. The lower this pressure, the better the design so as not to burn up power / generate heat. It does however have to be enough to bottom out the pump pistons back against the swash plate. Is this required pressure known? Sorry if already covered.
If it is below spec and the pistons aren't de stroking (= no traction flow) then it may be more crud downstream in valve after or inside the swash plate pump. Maybe better info in the pump manuf spec sheet.

Since this backpressure is collapsing to 15psi when the pump is stroked up, then we can say that charging flow has increased which doesn't sound right.

The output pressure of a good pump can legitimately be close to zero if no load on the wheels eg tractor jacked up. High pressure there only when wheels are loaded so you won't see pressure there just yet.

Since the problem had instant onset, maybe down a ramp on overrun when pressures are reversed, thinking crud, not wear....

Also, I'm not familiar with these JD models, but down here we see legislative safety "addons" that aren't necessarily documented on original designs.... typ a dump valve to drop the pump pilot oil to tank when tractor deemed unsafe to move ( seat switch, low brake pressure available, etc ).

 

[dustin63933]

Guys I am so sorry for not getting back to you. This forum was sending me updates to my email when I got replies but I never got any emails so I thought the thread died. But I came back here to update everybody on the fix. Apparently the guy we loaned this out to finally told us it came off the trailer while he was driving it and the back wheels touched the ground which made the hydrostat motor grenade on the inside.

The little brass shoes at the end of the pump just broke into pieces and score the housing up and damaged a couple other things up in there. I split the tractor and found the issue pretty quick. There was some brass pieces and steel in the tunnel of the tractor but they never did make it to the screen or else I would have found the problem faster.

Found a used hydrostat motor for $1200 shipped online. Installed it, all is well. Currently has about 10 hours on it since I fixed it. Thanks to everybody with your helpful suggestions, wish I would have known it fell off the trailer instead of just being driven off. The "buddy" is going to pay for all parts and etc for this.

For anybody scared to split the tractor, it was actually very easy being my first time. It was just time consuming but not complicated at all.

 

[Runner]

Thanks so much for the follow-up post on this. Assuming the tractor was parked in neutral, curious why rear wheels moving would grenade the hydro motor. Was it the sudden jolt or excessive speed?

 

[dustin63933]

I'm going to assume it was in gear. He wasn't going far with it so he didn't strap it.
But yeah I don't see how it moved in gear unless there's more to the story, Can't believe anything the guy says anymore. Needless to say he wont be borrowing the tractor again!

 

[oldnslo]

This response is based on the assumption that the hi low range selector was not in neutral when tractor rolled off the trailer when trailer was being towed.

If range selector was in gear them the HST motor is connected to the drive train and would act like a pump. The motor now pump would then try to drive the HST pump like a motor. The motor would be at full displacement and pump at minimum displacement so motor would see high pressure but no charge pressure so there would be no “return” flow to motor inlet causing the piston slippers to lift off and self destruct like in the pictures.

Like others said thanks for posting the problem and solution.

 

[dustin63933]

Lemme post some more pics in case years from now somebody stumbles upon my thread and this helps them out. Also anybody needing the manual dm me or cheapest I could find is $20 on google.

 

[oldnslo]

Dustin
Thanks for posting those additional pictures of that damaged motor.