JD 6400 Hydraulic Pressure

[russhog]

I have a problem with my 6400 transmission with a syncro transmission.
When you put it in gear it will not move unless the rpms are up around 1800.
The system pressure is 170 at startup but then drops to around 100 within a second or two and the low pressure light comes on.

I have replace the transmission pump, pump housing and all the valves in the house. Also replaced the main pump and charge pump for the hydrualics.

Any ideas about why it is dumping the system pressure?

 

[Cdeere]

I have a problem with my 6400 transmission with a syncro transmission.
When you put it in gear it will not move unless the rpms are up around 1800.
The system pressure is 170 at startup but then drops to around 100 within a second or two and the low pressure light comes on.

I have replace the transmission pump, pump housing and all the valves in the house. Also replaced the main pump and charge pump for the hydrualics.

Any ideas about why it is dumping the system pressure?

Did you ever fix the problem? We have run into the same thing and can’t figure it out. Thanks!

 

[rScotty]

Did you ever fix the problem? We have run into the same thing and can’t figure it out. Thanks!

I'd go down to the Vintage John Deere sub-forum and ask Tx Jim about that. He has a lot of JD knowledge.
Those old JDs with their closed center hydraulics are a world of their own.
rScotty

 

[Tx Jim]

rScotty
Thanks for acknowledgement BUT my personal JD experience stops with the 55 series tractors. I'm guessing Cdeere's 6400 has Power-quad trans which is similar to but not exactly to my 4255's Quad-range trans.

 

[Tx Jim]

Cdeere
Welcome to TBN. Please report your tractors symptoms & any diagnostics that have been performed.

Does your tractor have a Power-quad trans? If so have you checked any trans pressures. If it has PQ trans I think it's possible torsion damper could be at fault or trans hyd clutch could be slipping.