John Deere 955 won't move.

[Alumalite]

I had the bolt that holds the drive gear to the hydro break in my old JD 955. (I guess this is a fairly common problem). Following the service manual I pulled the hydro, replaced the bolt, fished out the broken bolt and washer out of the transaxle and put the whole thing back together. After replacing all the fluid I started the transmission bleed procedure, but the tractor will not move in forward or reverse now! I tried moving the shift lever to both fast and slow several times and it didn't do anything. It just acts like it's in neutral.
The rest of the hydraulic functions seem to be acting normally, the power steering is working, the bucket raises/lowers, etc. Is there anything I can check or try before tearing into it again?

 

[Williy]

Did you recheck to see if you have enough fluid??
Is it possible to have air in the system??

willy

 

[Alumalite]

That's what I originally thought it was too. I was working on bleeding the system when I discovered it wouldn't move. The service manual says to check the charge pump pressure, but I don't have the correct gauge. I did open the screw where the pump pressure is tested and bled the air out of it.
I also checked the charge relief valve, which looked fine.
The service manual also recommends checking the charge pump flow, but I don't have a gauge for it either.
I am stumped. The original repair was pretty straight forward (but a ton of work to squeeze the hydro out of the frame rails) so I am not sure why I have a new problem now.
I will go through the bleed procedure again and see if I can find any hidden air pockets. Thanks for the suggestion.

 

[Alumalite]

So, I can push the tractor forward and backwards in all 3 settings: slow, neutral, and Fast. I don't know if that will give any clue as to what's going wrong. I don't know enough about how these work to diagnose the problem.

 

[rScotty]

That's what I originally thought it was too. I was working on bleeding the system when I discovered it wouldn't move. The service manual says to check the charge pump pressure, but I don't have the correct gauge. I did open the screw where the pump pressure is tested and bled the air out of it.
I also checked the charge relief valve, which looked fine.
The service manual also recommends checking the charge pump flow, but I don't have a gauge for it either.
I am stumped. The original repair was pretty straight forward (but a ton of work to squeeze the hydro out of the frame rails) so I am not sure why I have a new problem now.
I will go through the bleed procedure again and see if I can find any hidden air pockets. Thanks for the suggestion.

Pressure gauges are pretty inexpensive. Check Amazon. Less than $20 and about that much again for fittings. A gauge would at least let you know if the pump is making pressure. Without one, I'd just be guessing.
Flowmeters are real expensive and even a lot of medium size tractor dealer shops won't have one. But there are ways around that if you know the pressures.

 

[Alumalite]

I will get a gauge ordered, I have been wanting one anyway. I will update you on pressures when I know. Thanks!

 

[gstrom99]

Which bolt broke? I don't have a repair/parts manual handy. Following, and awaiting your findings... Good luck.

 

[Alumalite]

Bolt "A" seen in this photo. The later models switched to a castle nut since it was a common failure point.

 

[rScotty]

Is that an output gear or does it drive the HST pump? It almost looks like an output. Would a lose nut cause enough gear slop to break the bolt? Maybe a larger exploded parts diagram would help.

 

[gstrom99]

Ouch! Thanks for the pic. I see where that failure would be bad...

 

[Alumalite]

It is the hydro output gear. The bolt broke and the gear (inside the transaxle) was loose. While the bolt was broken the output gear still slightly meshed with the gear inside the transaxle, so it would still drive, but due to the angle of the gears it would slip off and not go into reverse. I replaced the bolt and removed the broken bolt and washer from the transaxle, so it should be good to go now.
I am not sure why I am not getting any power to the transaxle. It acts like the hydro isn't pressurizing the output shaft. I didn't take the hydro apart when I removed it though, so I am not sure why it would randomly stop working. Oil levels are good. I followed the bleed procedure so I don't think I have an airlock, but I guess its still possible. All other hydraulic functions are working fine.
I guess the Hydro output may be spinning and not engaging the gear in the transaxle, but that seems pretty unlikely, there wasn't any change there and no way to adjust the gear mesh.
The transaxle may be stuck in neutral, but again, I didn't change anything in there either so it seems unlikely.
My best guess is the hydro output shaft is no longer spinning, but I don't know what would cause this. The swashplate is moving back and forth freely, so the top rocker pump in the hydro should be pressurizing the fixed plate pump, but I'm just not sure.
For more clarity on the original broken part: Bolt #60 broke. Bolt head and washer 59 were fished out of transaxle. It has been replaced and the hydro has been reinstalled.

 

[Alumalite]

Quick update: I was out of town for the weekend and when I came back I decided to bleed it one more time... and it worked fine. I guess I had a tenacious air pocket in there somewhere.

 

[gstrom99]

Good to hear you got it fixed... oh, and welcome to the forum.

 

[Josias Beekhof]

Hello,

I'm having pretty much the same problem right now. My 855 was working fine, going forwards and revese, but it was leaking oil on the input shaft from my supply pump. I replaced the seal (44 on exploded view) and this wasn't a big deal. But then i filled the tractor up again and it's doing te same; it doesn't go forwards or reverse and tried to bleed it for a long, but it doesn't work: Still no moving, while my hydraulics are working fine. My question is: How did you bleed your transmission? What are the recommended actions to take?

It would be nice if someone could help me out,

Greetings from the Netherlands.

 

[Johndeere3720]

Hello,

I'm having pretty much the same problem right now. My 855 was working fine, going forwards and revese, but it was leaking oil on the input shaft from my supply pump. I replaced the seal (44 on exploded view) and this wasn't a big deal. But then i filled the tractor up again and it's doing te same; it doesn't go forwards or reverse and tried to bleed it for a long, but it doesn't work: Still no moving, while my hydraulics are working fine. My question is: How did you bleed your transmission? What are the recommended actions to take?

It would be nice if someone could help me out,

Greetings from the Netherlands.

Personally haven’t dealt with this specifically on my 955 yet (although I’ve fixed plenty of other things on it). I can see if I can find that procedure in the service manual. Another great resource is there is a Facebook group specific to the 50, 55, and 70 series Deere compacts that’s a wealth of knowledge for these kinds of things. I’ll post a reply to if I can find that bleed procedure in the manual.