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Discussion Starter #1
I have a leak ,JD 400, near the rear crankshaft just behind the universal joint when I use the hydraulics the drip increases and then my undercarriage hoses and everything are wet with transmission fluid . anybody want to give me a guess what that is? thank you , Oregon Tom
 

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I'm a little...lot!... confused by your terminology. By "rear crankshaft" do you mean the shaft going between the engine and the rear end (hydro unit) ?
If so, probably a loose fitting or bad seal on charge pump. Remove seat pan, clean area, start tractor and try to determine EXACTLY where the oil is coming from. We can help you from there! Bob
 

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Discussion Starter #3
Thanks Bob, , yeah I was referring to the transmission pump housing the block area . it seems to be seeping out of the front end of that where the s
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haft goes. Heres a pict., the bottom of the pict. Is the correct orientation, Thanks again, Tom
 

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Tom, Most likely the seal in the charge pump, JD part # AT12820. Remove fender deck...watch for wires for lights & seat switch!..., clean area, and start tractor. (You'll have to TEMPORARILY jumper seat switch) and verify leak is in fact around OD of driveshaft and not somewhere else and running down to driveshaft !

Once you've verified it's the seal, remove drive shaft. You may need to slide engine forward to do this! Next, attempt to remove seal from charge pump housing. Clean surrounding area before removing seal! If seal comes out, lube shaft & seal and install new seal. If seal won't come out, remove 4 bolts and charge pump housing. Inspect shaft for wear at bearing & seal diameters. If OK, at this point, I'd replace the o-ring, needle bearing, and seal. When reassembling, everything must be ABSOLUTELY, POSITIVELY CLEAN!!!!!! Wash with solvent/parts cleaner, blow with air, wipe with hand. NO paper towels or cloth shop rags as these will leave lint !

Before you get started, I'd strongly recommend going to jdparts.deere.com and create your (free !) account. Enter a local JD dealer and you'll be able to get a price and if dealer has part in stock. After creating account, enter "400" in Model Search box, scroll down results to 400 lawn & garden tractor, then transmission pump housing. You'll find every bolt & part for your tractor.

Good luck and get back with additional questions AND RESULTS! Bob
 

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Interesting 400. I see you raised the rear fenders up to clear much larger tires. Looks well done!
 

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Discussion Starter #6
Tom, Most likely the seal in the charge pump, JD part # AT12820. Remove fender deck...watch for wires for lights & seat switch!..., clean area, and start tractor. (You'll have to TEMPORARILY jumper seat switch) and verify leak is in fact around OD of driveshaft and not somewhere else and running down to driveshaft !

Once you've verified it's the seal, remove drive shaft. You may need to slide engine forward to do this! Next, attempt to remove seal from charge pump housing. Clean surrounding area before removing seal! If seal comes out, lube shaft & seal and install new seal. If seal won't come out, remove 4 bolts and charge pump housing. Inspect shaft for wear at bearing & seal diameters. If OK, at this point, I'd replace the o-ring, needle bearing, and seal. When reassembling, everything must be ABSOLUTELY, POSITIVELY CLEAN!!!!!! Wash with solvent/parts cleaner, blow with air, wipe with hand. NO paper towels or cloth shop rags as these will leave lint !

Before you get started, I'd strongly recommend going to jdparts.deere.com and create your (free !) account. Enter a local JD dealer and you'll be able to get a price and if dealer has part in stock. After creating account, enter "400" in Model Search box, scroll down results to 400 lawn & garden tractor, then transmission pump housing. You'll find every bolt & part for your tractor.

Good luck and get back with additional questions AND RESULTS! Bob
What a big help Bob. Will the seal usually come out without having to open the unit?
 

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Discussion Starter #7
What a big help Bob. Will the seal usually come out without having to open the unit?
Bob, I took off the front plate to the hydro unit, do you recognize it from the attach
Pict? Why does the large geared washer loosely fit like This? Tom
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That gear is the actual pump. Oil enters when there's space between the teeth and then gets compressed (creating pressure) when the "gears" come into mesh and the space is eliminated. Bob
 

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A word of caution or at least something to be aware of:
The gear on the shaft is driven by a small pin, maybe 1/8" dia x 1 1/2" long. This pin is typically a loose fit in the shaft and can fall out (UN-NOTICED!).

As a quick comment on the looseness of the large gear: The small inner gear is driven by the shaft. The outer gear rotates inside of the housing, so it must have some amount of "looseness". Bob
 

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Discussion Starter #11
A word of caution or at least something to be aware of:
The gear on the shaft is driven by a small pin, maybe 1/8" dia x 1 1/2" long. This pin is typically a loose fit in the shaft and can fall out (UN-NOTICED!).

As a quick comment on the looseness of the large gear: The small inner gear is driven by the shaft. The outer gear rotates inside of the housing, so it must have some amount of "looseness". Bob
Good question about that pin, but I don't think I need to go deeper than what I've shown you. just to replace the bearings seal and the O-ring you know that 6 inch O ring so the little can I I shouldn't aggravate that at all cuz I'm not going that deep correct
 

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Discussion Starter #12
Good caution on that pin. But I shouldn't have to go further in , than what I need to , to replace the large O ring, bearing set and seal. Put the head cover back on , ready to go. That pin should not give me a problem,, correct?
 

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You're correct, no need to go deeper. I wasn't sure if you were going any deeper, so I mentioned the pin.

When doing your final reassembly, I'd get rid of the gloves. Many clearances inside a hyd system of less than .001" and a small piece of debris on your gloves can really hurt the system!
Wash parts...and hands!..., dry, oil all parts with hyd oil, and reassemble. So far, you're doing great! Bob
 

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Discussion Starter #14
Great feedback, thanks, My 1978 400 does not have a cooling fan near the u joint, where I'm currently working, I notice some 400, in u-tubes, have a fan..? Why do you think my 400 does not?
 

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Per the parts catalog, there's fan attached to the end of the driveshaft that attaches to the input shaft on the hydro, just as you state. I can only guess that someone made up a drive shaft when the original failed. At $902.40 for a new JD shaft, I can see why they made their own!

BTW, if you have zerks in your universals, now would be a good time to grease them! Bob
 

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Discussion Starter #16
So if I don't have a fan and it looks like there might have been some creative Design on that drive shaft is the fan Critical for cooling? I appreciate your knowledge and insights if you don't mind the questions as they keep coming, it sure does help me out on all those things that I'm not sure of.
 

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Tom, Thanks for the comment on my knowledge and insight, but it's all just a combination of JD parts catalog...to see what we're working on... and my general mechanical knowledge!
From parts catalog, the 400 should have an oil cooler and this should eliminate the need for a fan...but this is strictly a guesstimate! My 3xx tractors have a fan on the output shaft of the hydro. Perhaps you could find a fan and adapt? This would be a modification of the fan to mount on driveshaft as I don't believe (??) the 400 has an output shaft.

No problem with questions. I'll answer what I can or flat out say I don't know! Another source of information is Weekend Freedom Machines (wfmachines.com). Similar to this site, but 90% Deere tractor. It's a free site, just sign up and post away.
 

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Discussion Starter #18
Tom, Thanks for the comment on my knowledge and insight, but it's all just a combination of JD parts catalog...to see what we're working on... and my general mechanical knowledge!
From parts catalog, the 400 should have an oil cooler and this should eliminate the need for a fan...but this is strictly a guesstimate! My 3xx tractors have a fan on the output shaft of the hydro. Perhaps you could find a fan and adapt? This would be a modification of the fan to mount on driveshaft as I don't believe (??) the 400 has an output shaft.

No problem with questions. I'll answer what I can or flat out say I don't know! Another source of information is Weekend Freedom Machines (wfmachines.com). Similar to this site, but 90% Deere tractor. It's a free site, just sign up and post away.
I do have a oil cooler, when I re-fill the 400 with hydro fluid....I'm never sure of how much to add with the cylindars, I use the front two couples for cylindars too, so, do I fill the tank with those extended or half extended...how does one determine how much fluid to add?, My 1978 has a site tube to guide me for how much to fill.....Tom
 

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Conklint-The pump on a 400 is a Sundstrand 15 Inline. Current manufacturer is Sauer Danfoss. You can get a manual online. There are parts drawings all over the internet. But you aren't into it really that far. Yes, there typically is a fan attached to the drive shaft but it seems to be redundant with the oil cooler, so it seems reasonable to not sweat that it is missing. It doesn't actually move much air anyway. Maybe the fan would be helpful if you did a lot of long days pulling a plow.

Top off the fluid with all the cylinders retracted. That is the condition that the most fluid is back in the transaxle housing.
 

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Discussion Starter #20
Grandpajay, thanks for the input is really valuable information there's a lot of help on this site from several people I sure appreciate your help and if you don't mind I may ask you another question or two as I get these new parts ordered and put in thanks again , Oregon Tom
 
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