Sunstrand 15

Lee_K

Member
I have a John Deere 400 with a sundstrand 15 drive unit. The hydrostat is weak and so is the power assist steering. I measure about 200-300 psi at the front hydro outlets. My research says the likely culprit is the charge pump on the sundstrand. My question is Is it reasonable to rebuild/the charge pump part of the unit with out going into the rest of the pump/motor?

Thanks,
Lee
 
Hardest part about repairing/replacing the charge upmp is removing the drive shaft from engine to transmission.

Don't know that weak hydraulics are the pump. Relief valve for hydraulics and transmission I believe is on the steering gear/steering motor/pump.

Weak hydro transmission could be due to weak pressure/volume to the charge circuit of transmission, maybe. Is it weak in both directions? How many hours? Maintenance history?
 
Yes the transmission is weak in both directions. I also have a JD 318 which has a similar sunstrand 15U and moving the hydro control quickly forward or back will jerk your head off or spin the tires. The 400 whines a little then slowly picks up speed. Ive only owned the machine less than a year but the previous owner said he had recently changed all the fluids and filters so Im assuming that end is good. I always thought things seemed a little weak but it all got worse today. It is my understanding that the relief valve is on the pump. Can some one confirm this? The hour meter says 8xx hours but my understanding is that it was changed when the motor was rebuilt 20 years ago.

I will add that I mowed with this tractor as a kid 10 to 15 years ago until dad sold it to a friend. Even back then it was not as responsive as the 318, but I remember it being better than it is now.

Thanks,
Lee
 
Charge relief valve is on right side of housing to the rear of charge pump. Adjustment is by shims, don't loose them when removing plug. pressure is 135 plus or minus 45 psi.

Implement relief is on top of housing near charge pump, in front of the two charge check valves. Pressure is 900 plus or minus 50 psi. Adjustment is via shims.

Take charge check valves apart to clean and inspect as well.
 
The charge pump is a simple gerotor pump.

Once the driveshaft is off it's easy to remove the pump and inspect it for excessive wear, scoring, or other damage.

If badly beat up, new ones are around $400. I think I still have a good used one, should you be in the market for one after inspection of yours.

BTW, I ASSUME you've replaced the hydraulic filter?
 
If you put the front wheels against a high curb with engine at full speed and hydro lever full forward, will it kill the engine. It should. There is no high pressure reliefs for hydro, engine is it.
 
I have not personally changed the oil or filter. Should I start there? Looking at the book just now it says the filter should be changed twice as often as the fluid.

Thanks,
Lee
 
"I have not personally changed the oil or filter.


The filter is on the suction side of the pump, if clogged it would certainly affect pump performance.

May well NOT be the issue, but yet probably should be done first.

As to the oil, it certainly never hurts to change it, but unless it looks dirty or cloudy (from moisture) changing the oil isn't likely to fix the problem. (Unless someone has put the wrong oil in it.)

You could drain it into a CLEAN container and see what it looks like, if clear and free of debris you could consider reusing it (if cost is a concern).

Filter is part # AM39653, about $9 at a John Deere dealer, or WIX # 51410, any auto parts store should have that or be able to cross to their brand.

Recommended oil is John Deere "Hygard", aftermarket tractor transmission and hydraulic fluid that meets "J20C" specifications is a substitute.

Post back if any more questions.
 
Update,
Ive got a new filter and will change the first chance I get. I did the test with the wheels against a concrete wall. With the engine at full speed and the hydro full forward in low range spun the tires, in high range it just whined.

Thanks again,
Lee
 
Lee, the hydro I would say is not too bad but not perfect. Maybe getting the charge/implement pressure up would help by keeping the hydro loop full.

Take the implement relief valve out on the top of the transmission, near the charge pump, carefully. There are shims in the "cap", but looking for broken spring or something stuck holding it partially open. Should have 900 psi at a front outlet.
 
Further update,

I changed the filter and my pressure increased to 500 psi cold then after driving around a bit in high range it was 425 ish psi. I removed what I though was a relief valve on the side of the pump but there was no springs ect inside. It appears to just be a plug. Is there any sort of relief valve on the pump or is there one on the H3 control? Im assuming there has to be one some where. I will include a picture of the pump and what the inside of what I thought was a relief valve.

Also what is involved in removing the drive shaft? It almost looked like the front end (engine) would have to move to get enough clearance.


mvphoto55624.jpg


mvphoto55626.jpg
 
Do you have any sort of service manual, or are you "flying blind"?

If you download the manual below and look at Pages 23 and 24 you will find details of the charge pressure relief and implement relief valves.

I have an official "400" Technical Manual, but not at this location, that would be more specific.

Note what the first paragraph on Page 24 says, which I suspect MAY apply to the 400.

I'll try to find my "400" manual this weekend.
Sundstrand
 
I have been looking at that manual. This unit has no ports or valves on the left side where it suggests the implement valve should be (C in the picture). I took out H and there was nothing behind it. Reading some more forums about the 400 I think the only valve is on the tractors H3 hydraulic control.


Lee
 
Looks like something down the 'Hole". Did you try to fish it out?

Gained on pressure with just changing the oil filter!? Did you change the oil?

420 tractor has implement relief on the top of the housing forward of the two charge pressure check valves. Near to
the charge pump.
 
I used a small screw driver and a magnet and got nothing out. I expected there to be spring pressure on the plug. The top of the pump is in one of the pictures I attached. The only thing on top is those allen head plugs that I think are for guages.

I only changed the filter. The fluid looks clean to me. It is read which makes me think it is Type F ATF which is what is one of the recomended fluids.

Thanks,
Lee
 
(quoted from post at 13:47:34 05/30/20) Looks like something down the 'Hole". Did you try to fish it out?

Gained on pressure with just changing the oil filter!? Did you change the oil?

420 tractor has implement relief on the top of the housing forward of the two charge pressure check valves. Near to
the charge pump.

Your "420" hydro has a COMPLETELY different valve block setup than the O.P.'s "400".
 

Here's some info right from the DEERE SM-2103 service manual:

tiAYw8k.jpg


I believe what they are called the "bypass valve" is the relief valve, "D" in the following drawing:

JyMlxRk.jpg


See note below that explains why no charge relief valve is required in this specific system:

IFnXfQ1.jpg


I would drain oil and see what metal filings are in it (if any) BRASS would indicated failing "slippers" on the hydrostatic pump and/or motor pistons.

If no (or very little) brass, I would move on to having a look inside the charge pump.
 
I took that relief valve (D) apart and it all looked good. I did notice there were no shims. I also drained the oil just now and found mostly very fine, but metal shavings. I could get them to move around with a magnet so I'm confident they are not brass.

It looks like I will be digging into the charge pump. What is involved in removing the drive shaft? Will the motor have to come out? Also is there any reason to refill the hydraulic fluid till Im done working on the charge pump?

I really appreciate everyone's help so far. THANK YOU!

Thanks,
Lee
 

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