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Two 400s, MTD 990, Sears 10XL
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Discussion Starter · #1 ·
All,
I talked the wife into letting my buy a "backup" 400 last winter in case our daily driver 400 went down. I knew when i bought it that it had a hydrostatic input seal leak but did not realize how bad of a leak it was until i got it home. The tractor also came with a rear PTO and tiller so i couldn't check the hydraulic oil level. Well, when i removed the seat pan to pressure wash the machine i saw the sight tube and there was no fluid at all in the tube. The machine still moved and operated normally but it took over 3/4 of a gallon of fluid to get her back to a normal level.
The machine was also horribly dirty with all the hydro fins filled with dirt, the hydraulic fluid makes an excellent glue.
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After pressure washing I ran the machine and confirmed the oil was being slung out of the driveshaft input seal. Off to Greenpartsstore.com to purchase a new input seal and o-ring. I didn't feel slop in the input shaft so decided not to replace the needle bearings behind the seal.
 

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Two 400s, MTD 990, Sears 10XL
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47 Posts
Discussion Starter · #2 ·
After the parts arrived my middle daughter and I started tearing into the old girl. I have done driveshaft work on my MTD 990 and was able to knock out the roll pins connecting the driveshaft to the u-joints thus allowing me to remove the driveshaft from the pump without having to move the engine on or the axle. Well the 400 shaft is welded to the yokes so we ended up moving the engine forward.
Moving the engine was not overly difficult but also not easy. The 400 is repowered with a B&S 23 HP Vanguard, when you move the engine forward the exhaust hits the grill shroud and the oil filter hits the front engine mount. After removing the exhaust we ended up placing wood blocking between the engine and the mounts so we could slide it forward far enough to remove the driveshaft from the pump.
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After removing the driveshaft we removed the charge pump. It was at this time i noticed two issues. When attempting to remove the driveshaft i saw that the driveshaft is only fixed to the engine output shaft and is allowed to slide loosely on the charge pump input shaft. Because the driveshaft is not pushed far onto the output shaft of the engine the yoke on the charge pump input shaft had been rubbing against the seal and charge pump casing. You can see the worn area around the seal in the picture below.

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As i can still read the stamping on the seal i do not believe the yoke caused the leak. I pulled the old seal and placed the new seal slightly farther back in the pump in order to avoid the wear mark on the input shaft that the old seal was riding on. I then replaced the old o-ring and reinstalled the pump.

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I also discovered the woodruff key was worn and distorted. Unfortunately i did not have the correct key on hand and had to go to three different stores to find the correct one the next day. After sourcing the key I did my best to push the driveshaft farther up on the engine output shaft and reattached the driveshaft to the charge pump. It's not the perfect solution but there is a larger gap between the yoke and the charge pump face than before.
The u-joints appeared in to be in good condition, thank goodness, and so i did not replace them while the shaft was loose.
In the end I put it all back together and fired her up and....voila! no leak! If i had to do it again i believe i wouldn't have made any changes to the procedure i followed. Although i've never pulled the transaxle from one of these it appears to be more work than moving the engine forward, especially now that i know what needs to be done
I used this excellent post to prepare for the job in case you are looking to do the same. Best of luck and thanks for reading! John Deere 300 and 400 Series Transmission Input Seal...
 

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So there might be an argument for a two piece driveshaft when I need to repower. Thanks for the write up. Been there, done that-although I went with the transaxle move rather than engine move.
 

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Two 400s, MTD 990, Sears 10XL
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Discussion Starter · #6 ·
So there might be an argument for a two piece driveshaft when I need to repower. Thanks for the write up. Been there, done that-although I went with the transaxle move rather than engine move.
How did you find sliding the transaxle back? If i had to move the engine again i'd say it would take maybe 15 to 20 mins. Thanks.
 

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That's how I ended up with four 400's and a 420. No limit to that kind of thinking, not even theoretical. You can keep buying more and more of them by applying the same logic. It's great.(y):D
I talked the wife into letting my buy a "backup" 400 last winter in case our daily driver 400 went down.
 

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Two 400s, MTD 990, Sears 10XL
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47 Posts
Discussion Starter · #10 ·
Why didn't you pull the 4 bolts to remove the hood and hood mount?
That's a possibility for next time. It would have given me a bit more wiggle room but removing the exhaust was also only 4 bolts and gave me enough room to slide the engine forward as far as needed.
BTW, that battery hold down is an electrical nightmare waiting to happen. It's another left over from the previous owner and is on my list of things to remedy.
 

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After about 15 years I finally got good at that. Relatively speaking I mean. It's still a real PITA to get the brackets to mate up with the bolts. Just takes fewer tries now.
Taking the hood off of a 400 is a pita. It’s not like the 300’s with 4 bolts unfortunately 😬
 
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