Green Tractor Talk banner

1 - 20 of 34 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1
I have a 75 JD400, love it -runs great, it's been very reliable and I heavily depend on it for manure management on my small acreage. Suddenly, I'm using it the other day and it mysteriously stops moving into forward or reverse. Checked the 2-speed control (thinking maybe I bumped it into Neutral, if that's even possible), it's fine. Tried both low and high, nothing. You can probably tell by now that I'm not very mechanically inclined but I did know enough to check the fluid. It was low (didn't register on the dipstick), so I topped it up - still nothing. So I drained the oil and replaced it with Hygard Low Viscosity, replaced the filter, etc (it was overdue for this). Still nothing. I checked to confirm the brake wasn't accidentally locked on, nope, brakes are not on. Checked the linkage, it does look OK to me - I don't see anything broken, but the hydrostatic lever seems fine, everything appears to be connected and it does move the rod that goes into the side of the transmission. I'm at a loss as to what this could be. Full movement in the FEL and the rear PTO is working (so I'm thinking it's not the hydraulic pump). I looked online at the cost of replacing it - OUCH, sticker-shocked, I'm . I'm back to the drawing board feeling determined to get this ol' girl movin' again It really is the perfect tractor for what I need. I've had a couple guys out here to take a look - much more skilled than me. Without investing alot of time and effort, we haven't been able to diagnose it--neither had tractor experience. I've been reading these forums and although there's a wealth of information on here, I can't find anything that helps this specific situation. I'm really hoping there's someone on here that has experienced something similar, or can point me in the right direction as to what to check. I'm willing to put a new transmission in it, but I'd hate to replace the entire transmission only to discover it was something else. I would appreciate any advice!
 

·
Registered
Joined
·
9,900 Posts
The loader and rear pto are driven off the front pto, the hydrostatic is run off the driveshaft. Is your power steering working like it normally does?


I think your at the point of pulling the fender pan no matter what the answer to that question is. It’s not hard, just awkward.
 

·
Premium Member
Joined
·
5,994 Posts
Is your power steering working like it normally does?
Good question


Is the drive shaft rotating with the motor and is it turning the input shaft of the transmission?
 

·
Registered
Joined
·
19 Posts
Discussion Starter #4
Thank you for your replies. Power steering was working fine last time it moved. I’m pretty clueless when it comes to this stuff, but is there a way to check it even when the tractor is unmoveable? I removed the fender deck to get a better look at the linkage. I’ll take a look at the drive shaft tomorrow.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #5
Yes, the drive shaft is rotating when the engine runs and it appear to be turning the shaft that goes into the transmission. The linkage doesn’t seem right to me though. When I move the hydrostatic lever from Neutral I to the fully forward position, it rotates the shaft that goes into the transmission but only very slightly, maybe 3/8” (both sides of the shaft move equally)? Shouldn’t it rotate it more than that. And it doesn’t appear to rotate it at all when I put it into Reverse? Could this just be a linkage way out of adjustment? When I engage the hydrostatic lever at full throttle, it feels like the machine wants to move, kinda nudges a bit like it wants to move?
 

·
Premium Member
Joined
·
5,994 Posts
Did the steering work? Reason that rydpls asked is the pump that supplies pressure for that is the same one as that supplies pressure for steering. It helps narrow down where the problem is.

And it doesn’t appear to rotate it at all when I put it into Reverse? Could this just be a linkage way out of adjustment?
. If I remember right it should rotate half as far in Reverse as Forward.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #7
Probably a really dumb question, but how do I check the steering if it doesn’t move? I have it on the ground. Do I put it up on blocks? If not working, would the steering feel stiff, or? Appreciate your input - I am at a loss finding local resources to help me with this!
 

·
Registered
Joined
·
9,900 Posts
The 400 hydraulic assist power steering isn’t great, but it should still turn while sitting still on concrete, maybe yours was already so worn you only have manual steering where it takes serious effort to turn sitting still.

I would start inspecting your hydro linkage, maybe disconnect it and try turning the hydro input by hand and exercising that end looking for slop.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #9
Steering was easy last time I drove it. Just tried to move the steering wheel while on the ground, lots of play before the wheels responded and then it was VERY stiff to turn the wheels. Anothwr dumb question, but which pump is used for both the steering and the hydrostatic? I was told that there’s usually a loud whining noise when a pump fails but there’s no noise, so I kind of ruled that out? I did try to manually turn the shaft with the engine running and it still didn’t move.
 

·
Registered
Joined
·
1,425 Posts
Have you run your tractor and let it get nice and warm AND then checked the fluid again? I got my 400 going again this year in order to sell it (sadly let it go but that's life) and it was doing the same thing as you describe. I had to add fluid, quite a bit of fluid.

There is only one pump on the tractor. It could be worn out. How many hours are on the tractor?

If your FEL is stock it will have it's own pump on the front PTO. Sometimes people will use the tractor hydraulic pump to power the FEL but generally that makes it really slow to operate.
 
  • Like
Reactions: Herminator

·
Registered
Joined
·
19 Posts
Discussion Starter #11
It’s got a JD20 FEL and I’m pretty sure it’s powered by the one pump - the pump has 2 lines connected to the top of it so I assume it’s one for front implement and one for rear? So bring both the front are rear PTO are working, can I eliminate the pump as an issue? I was looking at the Sundstrand 15 manual for the transmission and trying to follow their troubleshooting flowchart. After checking oil and linkage, it says check the bypass valve on the pump - comparing to the diagram, I don’t see such a valve. I’m at the point of wanting to toss this thing and bite the bullet and buy a new one but it’s been such a good reliable machine, I was hoping I could get it working again.
 

·
Registered
Joined
·
9,900 Posts
The front and rear tractor pto are driven by the front crank shaft. The 20 loader hydraulics are 100% independent of the drive and power steering system.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #13
Thanks for all your help. So it sounds like it’s either the main pump or transmission? If I was good at mechanics I would do everything I can to fix it but I’m a single woman running a ranch - I’m so done with it, I’ve started the process of buying a new machine. I’d just hate to send this one to the junkyard if it’s something minor like a bad valve. It runs great. Perhaps it has served it’s time, it’s been great for 25 years, a workhorse!
 

·
Registered
Joined
·
19 Posts
Discussion Starter #14
I’m getting closer to diagnosing this thing. We pulled the implement relief valve from the pump (which is still installed) and the pin was bent - not good right? Anyone ever seen this before - what would cause the pin in the valve to be bent - years of wear and tear, or? Then removed the valve bolt from the opposite side of the pump - I think it’s the charge relief valve - and there’s nothing there. Like what the heck - do I need to remove the pump to really get in there to pull out that valve? Best case, maybe I can replace the 2 valves? Worst case, replace the pump? Not sure where to go from here.
 

·
Registered
Joined
·
1,425 Posts
Some pictures would help this thread. Do you have a factory service/maintenance manual? It has a trouble shooting section for the hydraulics and even how to rebuild the pump, if that's what is wrong.

Do the hydraulic lines for the FEL go to a pump attached to your front PTO or do they go to some place on the tractor?
 

·
Registered
Joined
·
19 Posts
Discussion Starter #16
The saga continues. I’m trying to check part #1 in the attached drawing - I am told by Sundstrand and JD that these are prone to fail. But how do I move the drive shaft to get inside the housing - I haven’t removed the pump but they are saying it’s an easy fix so I’m hoping I don’t have to? Also attaching a pic of the shaft and the front of the pump.
741388

741389
 

·
Registered
Joined
·
152 Posts
Sadly, to get the driveshaft off to access the pump, either the engine has to come forward about an inch or the transaxle has to move back about an inch. Neither are an evening job, but doable with some fortitude.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #18
Thanks grandpajay! That’s what I was afraid of - when they say it’s easy sounds like it means it’s easy when the hydrostatic is not installed in the tractor! What do you think is easier, move the engine forward or tranaxle back. Replaced the starter and lifting that engine was a long painful process.
 

·
Registered
Joined
·
152 Posts
I rebuilt my driveshaft and moved the transaxle back to get it out. Another time I broke an axle and had the transaxle out again. I found a replacement transaxle on Ebay that included a pump and just replaced the whole unit. I haven't checked recently but there are a number of 400's being parted out regularly and that could be an option. I was expecting to see a driveshaft fan, but maybe there wasn't one in 1975. Driveshaft looks kind of tight to the pump. There should be enough space to allow the driveshaft to float on the pump input shaft-maybe 1/4" or so. Here is a pic of a seriously modified 400 (and a couple others in the herd):
741405


Here is the transaxle swap:

741406


Changing a pump on a transaxle is straight forward:

741407


This is where the pin goes in the charge pump (sprocket looking gear). I detailed out my old pump and have it on the shelf should I get inspired to put it in.

741408
 

·
Premium Member
Joined
·
5,994 Posts
I agree. Transaxle back. They are correct. Easy once the hard part is over
 
1 - 20 of 34 Posts
Top