JD 4400 HST transmission chatters

[texasranger556]

Hi guys, long time lurker first time posting. Last year I bought a 4300 with a loader. Then I started looking for a backhoe for it since I'll be building a shop soon. I ended up finding a 4400 with under 500 hours in better shape complete with a 430 loader, 48 backhoe, mid PTO, foam filled R4 tires, etc. Second owner had it since 20 hours at a small farm and stored under a car port or barn. Looked good and the price was right so I bought it. The 4300 will be for sale soon once I fix some minor issues with it.

Dad picked up the 4400 for me and noticed that when you first hit the hydro pedals, it doesn't move unless you give it about 1/2 throttle, then it chatters like it has air in the system. Also runs away going downhill sometimes, but has plenty of power pushing dirt and the steering/loader/hoe all work great. We've worked on a fair number of hydrostatic lawn tractors so decided since the fluid didn't smell the best (suspect it is the original fluid) maybe the plates in the hydro were scored allowing loss of pressure. Pulled those out and weren't too bad, but resurfaced them anyway. New JD hydro fluid, filters, suction screen cleaned, etc. Drives a little better but still not nearly as smooth as my 4300, and still the dead pedal when first started.

It's sitting in dad's garage at the moment 5 hours away, I hope to get it hauled to my place soon and better investigate the transmission.

So, do the symptoms ring any bells?
It is my understanding that the transmission gets charged from the power steering circuit. Since the steering works great (better than my 4300), what does that leave to check?

Thanks! Ryan

 

[beenthere]

Pulled those out and weren't too bad, but resurfaced them anyway.

What is involved when pulling out these plates in the hydro? You make it sound like a minor job.

If not one already, better get the service tech manual for the 4300 and the 4400 (all in one anyway).

:welcome: to TBN

 

[texasranger556]

You have to split the tractor and disassemble the HST. Not all that complicated (relatively speaking) but it is tedious and does take time.

I plan on getting a manual, what is the best place to order from?

 

[Kyle_in_Tex]

If it were the later model with the ehydro, I'd say you have the match load switch on and that is how they work. Not sure what else to tell you.

 

[texasranger556]

If it were the later model with the ehydro, I'd say you have the match load switch on and that is how they work. Not sure what else to tell you.

I've driven an ehydro before, I can't imagine why anyone would use that function. It's like you're controlling the transmission with a rubber band.

Started looking through the tech manual, my best guess is a problem with the charge pressure relief valve. Either a broken spring or debris caught under the poppet letting the pressure drop too much at low RPMs, and while the tractor is not running maybe it's letting the oil drain out of the pump. That's making an assumption that the relief dumps to reservoir, which the manual is not clear on.

Now I just need time to check it out

 

[oldnslo]

texasranger,
what type of control in your HST? Is it direct linkage from the foot pedal to the swashplate or some form of servo control taken from a pilot pressure? On my Branson it does not feather from start at low RPM's which I suspect is due to the "neutral" valve having to large of a dead band but once moving it moves smoothly.

Does your JD have some form of 'neutral" valve that could be sticking?

 

[texasranger556]

The foot pedals appear to attach directly to the swash plate on the pump, no servos or pilot controls that I'm aware of.

When I compare between my 4300 and 4400, it's night and day difference. The 4300 will crawl smoothly out of the garage at idle while the 4400 just sits there with the pedal mashed all the way down. Give it some throttle and it starts moving but chatters. Low charge pressure seems to fit the symptoms.

 

[oldnslo]

The foot pedals appear to attach directly to the swash plate on the pump, no servos or pilot controls that I'm aware of.

When I compare between my 4300 and 4400, it's night and day difference. The 4300 will crawl smoothly out of the garage at idle while the 4400 just sits there with the pedal mashed all the way down. Give it some throttle and it starts moving but chatters. Low charge pressure seems to fit the symptoms.

Agree that low charge fits the description but it would almost have to introducing air / drawing a vacuum to get the chatter and freewheeling effect.

If charge is fed from steering and the steering works fine that eliminates the pump so will have to determine were the flow is going when it leaves the steering circuit.

good luck

 

[texasranger556]

Agree that low charge fits the description but it would almost have to introducing air / drawing a vacuum to get the chatter and freewheeling effect.

If charge is fed from steering and the steering works fine that eliminates the pump so will have to determine were the flow is going when it leaves the steering circuit.

good luck

According to the schematic (which could use a little more detail), the only logical place the charge circuit oil can escape back to the reservoir is through the charge pressure relief valve. It's certainly not leaking externally.

I agree with you that to chatter as bad as it does it seems like it would have to be ingesting air from somewhere, so if the valve looks alright I'll have to get a gauge to check for at least 100psi of charge pressure and see if the oil is foamy at the check port and go from there.

 

[dfkrug]

Started looking through the tech manual, my best guess is a problem with the charge pressure
relief valve.

There are pressure test ports for charge pump and the FWD/REV functions. You should get something
like 150psi for the former, and nearly 6K psi for the latter 2, on relief. You can get at the test
ports thru the hole in the bottom of the housing. It is a tight fit, I know.