2640 hydraulic issue

About a month ago we replaced the main hydraulic pump.
We had nothing at all no brakes no steering. All hydraulics worked great.
Now it has done the same thing. We warranted the
pump. Put the new pump in and still nothing but this time we
have brakes but Im not sure if its just because they havent
bleed off yet but you can hear hydraulic noise just a bit at the start and then nothing. We have changed the transmission
pump screen. The main hydraulic filter and the filter relief
valve have been changed. New oil. Reservoir above pump is
full. What am I missing? Priority valve? Makes a little more
sense now that this time I have brakes.
 

Hyd brake operation on JD utility tractors such as your 2640 is dependent on trans pump being able to replenish oil level in brake valve reservoir. Main(front) hyd pump has no bearing on operation of brakes. Sounds as if you need to perform detailed hyd diagnostics before replacing any more hyd pumps.

Have you checked hyd oil reservoir suction screen for clogging? Have you checked hyd filter relief valve to be sure it's not stuck open? Does this tractor have options of hyd hi-lo &/or hyd pto? If so have you checked trans pump GPM with both hi-lo in both speeds & with pto in both on & off positions?

Does this tractor have a frt end loader? If so what type valve(ind or scv) controls loader?
 
Yeah we were unsure if my pump was the problem but it does not appear to be the case.
We swapped filter relief valve with a new one. The screen was replaced when first pump was put in.
Filter also. I pulled both out this second time and cleaned screen and replaced filter again just to be sure. I have not gone down the road of transmission pump as every time I check the reservoir its full.
I realize if pressure is low it will cause a problem long term but it should at least be able to supply steering for 10 to 30 seconds with or without cavitation till that tank was empty it doesnt even act like its trying.
I guess Ill start building jumper hoses and go buy a gauge set...
 

Good diagnostics is more important than changing components such as hyd pumps!! Priority valve is in hyd circuit after power steering so the priority valve is not limiting power steering.

DOES YOUR TRACTOR HAVE A FRONT END LOADER????
 

The front pump is the last thing that fails , not the first . It won t move oil if the elastomer drive has failed . Or if the front pump is not having oil pushed up to it by the low pressure pump system in the transmission .
 

I seen a fellow all proud of his independent loader connection .
He was right on with the supply connection into the high pressure line that supplies the SCV .
However he had ran the return line direct into the transmission case . Instead of into a ported oil filter cover .
 
(quoted from post at 19:20:11 03/25/23) Yes to the front end loader plumbed separately not scv
controlled.

I suggest that you perform a simple test. Disconnect FEL control valve return oil hose from tractor & cap orifice on tractor where return hose was attached. Now place open return hose in open hyd filler hole behind seat or a clean container. With FEL control valve levers in neutral start engine & no oil should exit open return oil hose. If return oil hose attaches to ported filter cover with return hose removed from filter cover engage starter for 15 seconds with clean container under opening with foot pedal released. There should be about 1.25 gallons of oil in container. With hyd oil at operating temp., 3 pt raised, engine at idle speed look inside opening hyd filler hole for moving oil. Moving oil indicates faulty rockshaft control valve seals.
 
Hey,
I worked for a Deere dealer during the vintage of the early 40 series Dubuque tractors. We experienced a fair amount of problems with these tractors cracking hydraulic tubes in the area of the shift levers under that cover. This would often cause the transmission pump oil to leak directly back into the transmission and not charge the main pump so you'd have no hydraulics. The brakes also received oil from this pump so in time you would lose the brakes also.The pto clutch also was operated by this pump. You don't say if your pto works or not. This may or may not be your problem but it was usually pretty easy to see. Pull the cover off and start the tractor. If you see oil spraying around in the case that's your issue. It requires splitting the tractor to fix those tubes. Good Luck! John
 

I'll advise not to start JD utility tractor of this era('65-'92) with shift cover removed unless one uses a piece of looped hose to join the 2 larger diameter tubes together that are visible after removing shift cover. With cover removed one can pressure each tube utilizing compressed air while listening for escaping air. Escaping air would indicate a leak in tube or tube sealing ring.
 
Good point Jim. I did forget to mention that you need to install a jumper tube on those two exposed tubes. Compressed air works also as long as you have a good supply.
 
Figured Id post an update on this. Its spring and been crazy busy. So the pump that worked for a month locked up solid and sheared the splines on the front shaft. Upon removing top shifter cover I did peak down with a borescope where I had seen brazing on those internal tubes on a neighbors tractor that got a clutch shaft seal. Sure enough theres splitting on the far right left internal tube. Id be willing to bet that John is right on the money and looks like I have a second one to split in 3 pieces to put a new tube in it.
 
(quoted from post at 16:37:14 04/13/23) Figured Id post an update on this. Its spring and been crazy busy. So the pump that worked for a month locked up solid and sheared the splines on the front shaft. Upon removing top shifter cover I did peak down with a borescope where I had seen brazing on those internal tubes on a neighbors tractor that got a clutch shaft seal. Sure enough theres splitting on the far right left internal tube. Id be willing to bet that John is right on the money and looks like I have a second one to split in 3 pieces to put a new tube in it.

You do not need to split in three pieces. This is not a johndeere powershift.
The transmission can be pulled out of the clutch housing very easily.
 
(quoted from post at 01:43:28 04/14/23)

You do not need to split in three pieces. This is not a johndeere powershift.
The transmission can be pulled out of the clutch housing very easily.

One must split JD utility tractors built between '65-'92 between clutch & trans housings to remove trans components(shafts/gears).
 
(quoted from post at 05:03:17 04/14/23)
(quoted from post at 01:43:28 04/14/23)

You do not need to split in three pieces. This is not a johndeere powershift.
The transmission can be pulled out of the clutch housing very easily.

One must split JD utility tractors built between '65-'92 between clutch & trans housings to remove trans components(shafts/gears).


Exactly whatI said, That is tractor in two pieces,not three like the OP said.
 

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