JD855 Moving Slower

[memse]

My 1991 John Deere 855 has been moving slower & slower over the last few months. I don't use it much as a homeowner but it's now to the point that whatever is wrong needs to be fixed. I've learned that the 855 has 2 hydro pumps and the pump for attachments works fine (bucket & 3pt hitch works fine). The other pump is for the hydrostatic transmission. When driving the 855's forward motion has become slow and gets slower even on level ground. As the machine slows its forward motion the engine RPM does not drop from its full throttle speed (I changed inner/outer air filters recently).

It's been awhile so I thought maybe a hydraulic service would help. I just cleaned the fine steel mesh filter, installed a new spin on hydro filter (getting the old one off was almost a deal breaker!), and changed the fluid which did not help with this problem. Now I'm wondering if there is a PSI adjustment for the transmission pump. I watched a YouTube video on making a PSI ajustment for the attachments pump on JD755/855/955 but it didn't cover the transmission. Before watching this video I did not know that adjustments can be made to my tractor's hydraulic system to set its required operational PSI level!

Any help troubleshooting this problem will be appreciated.

 

[5030]

Hope you didn't use cheap Tractor Supply fluid in place of the JD HyTrans?

 

[oldnslo]

Is it slow going both forward and reverse? Any noticeable new sounds or change in sound from cold to hot?

Not sure but first thing to check is the charge pressure for the hydrostatic pump. Instructions should be in the service manual.

 

[Leejohn]

Are your fwd and rev foot controls even and does it want to creep any? Could be you are not getting full travel and that is adjustable. I just rebuilt a engine on one and there's would creep a little. They said just not to fix, so I can't tell you how to fix for sure. There should not be any play or very little in the fwd and rev foot controls.

 

[memse]

Is it slow going both forward and reverse? Any noticeable new sounds or change in sound from cold to hot?

Not sure but first thing to check is the charge pressure for the hydrostatic pump. Instructions should be in the service manual.

Not sure about being slow in reverse and it seems like the transmission was making more noise. I've only run the tractor for a couple mins since changing the hydro fluid so I need to check reversing. The pressure test is a good idea so I'll look into buying a pressure gauge. My operator's manual doesn't have any details about checking the transmisson pressure but does tell how to adjust the rockshaft.

 

[memse]

Are your fwd and rev foot controls even and does it want to creep any? Could be you are not getting full travel and that is adjustable. I just rebuilt a engine on one and there's would creep a little. They said just not to fix, so I can't tell you how to fix for sure. There should not be any play or very little in the fwd and rev foot controls.

Good idea. I'll lube the foot controls and make sure that there is no obstruction limiting the forward control pedal.

 

[memse]

Hope you didn't use cheap Tractor Supply fluid in place of the JD HyTrans?

Bought JD HyGuard hydro fluid & filter at local dealer.

 

[oldnslo]

Not sure about being slow in reverse and it seems like the transmission was making more noise. I've only run the tractor for a couple mins since changing the hydro fluid so I need to check reversing. The pressure test is a good idea so I'll look into buying a pressure gauge. My operator's manual doesn't have any details about checking the transmisson pressure but does tell how to adjust the rockshaft.

Rock shaft is a complete separate system from the HST.

Charge pressure is usually low in the 100 - 350 PSI depending on transmission style. Noisy is also indication of possible cavitation in the charge circuit.

 

[WinterDeere]

It's been awhile since I've worked on an 855, but I used to be intimately familiar with them, as that was my primary tractor for many years.

I remember the pedal linkage on them was troublesome, and something as stupid as the driveshaft tunnel cover (between foot boards) being loose could cause the problem you're experiencing, although this would present as pedals that become much more difficult to depress.

There's a mesh screen at the bottom of the transaxle, the lower elbow fitting of the return tube that runs up the back of your tractor covers this screen. You should have removed and cleaned or replaced it when you changed your hydro fluid, but I suspect it could have been missed if you were not working from a service manual. These seem to be some combination of damaged or clogged, on many old machines of this model and vintage.

Did you remove and clean or replace that screen?