B7800 Lost Power

[Minerboyd]

I have a used B7800 and have only used it about five times, today when I tried to use it, the engine seemed to have plenty of power but when trying to move it forward or in reverse in either Medium or High gear it moved very slowly with very low power. I checked the transmission fluid level and it was within the acceptible levels but it was on the low end about 1/8" to 1/4" from the bottom marker. Could the problem be with the low level of "Super UDT" in the transmission case? What else should I check? I made sure the PTO's were disengaged and nothing else appears to be wrong with it other than the very low power and speed when the tractor is under any kind of load/ the greater the load the less power the tracter appears to have. Full throttle up a small incline and the tractor wont move forward all. Same thottle going down the same slope, and it runs fast with no problems noticeable.

Any help that can get me looking in the right direction (forward) would be appreciated.

 

[Eric McCarthy]

Possibility that the clutch is starting to go if it'll barely move out of its own way.

 

[Stumpy]

Works ok in low gear? Eric's probably right. The clutch is worn out or out of adjustment. Definitely sounds like the right symptoms. Careful running it too long like that, you could over heat and glaze or crack the flywheel.

If you want more confirmation before tearing into it; is there any chance you can hook up a PTO driven implement? If it won't spin that properly either then it's almost certainly the clutch.

 

[Minerboyd]

Works ok in low gear? Eric's probably right. The clutch is worn out or out of adjustment. Definitely sounds like the right symptoms. Careful running it too long like that, you could over heat and glaze or crack the flywheel.

If you want more confirmation before tearing into it; is there any chance you can hook up a PTO driven implement? If it won't spin that properly either then it's almost certainly the clutch.

Thanks for replying to my question but even though it made sence at first the more I thought about your reply the more I wondered how it could be the clutch. Since the B7800 has a Hydrstatic Transmission how could the clutch have anything to do with its ability to move forward or reverse in any gear? I thought the Hydrstatic Transmission used hydraulic fluid (oil), forced through a pump to drive the tractor without the use of the clutch.
According to one website I read: "The hydrostatic transmission uses hydraulic fluid forced through a pump to drive the tractor. This fluid drive system is controlled by a foot pedal or a hand lever. The speed of the tractor is maintained by the amount of fluid the operator allows to flow through the system. A benefit of the hydrostatic tractor lies in its ability to provide continually variable speeds without the need to clutch and shift gears. By simply moving the hand lever or pushing a foot pedal, the tractor's speed and torque can be adjusted on the fly. "
If the speed of the tractor is maintained by the amount of fluid allowed to flow through the system without using a clutch, how could the clutch have anything to do with the probem I described on my tractor.
I am wondering if having the fluid level at the lower end of the acceptible level mark on the dipstick could be enough to cause the problems I am having.
If not what else should I check and what tests could I run to find or verify the problem?
Is there a belt that drives the transmission oil pump that could have become loose or is there anything else I should be checking before paying to have it taken the 50 miles to the nearest Kubota dealer for servicing?
We bought it less than two months ago and it was supposidly totally overhauled and rebuilt just before we bought it.

 

[kubotasam]

The clutch is between the engine and the hydrostatic transmission. If the clutch is slipping then no power (or reduced) can get to the hydrostatic transmission.

 

[Stumpy]

Exactly. The clutch allows you to disconnect the hydrostatic transmission so you can shift the range transmission and the PTO (though I think that can be engaged on the fly).

Well I'd make sure the free play is set correctly first. Push on the clutch pedal. You should feel it travel a short distance without much resistance and then have heavier resistance for the rest of the travel. What you're feeling is the throw out bearing engaging the clutch fingers. Ideally the pedal will have about 1/2 to 3/4 of an inch of travel before the bearing touches the clutch fingers. It's possible (though unlikely) that they changed the clutch but set the free play wrong and the clutch is being held partially disengaged.

If you don't feel any free play then you should try adjusting the clutch linkage. On the left side of the tractor forward of the clutch pedal you'll see a rod that's threaded on both ends with nuts. It connects the pedal with a rod sticking out of the transmission. Break the nuts loose (one of them is going to be left hand threaded) and twist the rod to change it's effective length. Lengthen the rod to increase the free play. You want around 10-15% of the pedal's travel to be free play.

 

[65specialk]

Make sure your brake pedals are releasing. MY B 7800 sticks and no way to lube it easily. Very common problem.

Exactly. The clutch allows you to disconnect the hydrostatic transmission so you can shift the range transmission and the PTO (though I think that can be engaged on the fly).

Well I'd make sure the free play is set correctly first. Push on the clutch pedal. You should feel it travel a short distance without much resistance and then have heavier resistance for the rest of the travel. What you're feeling is the throw out bearing engaging the clutch fingers. Ideally the pedal will have about 1/2 to 3/4 of an inch of travel before the bearing touches the clutch fingers. It's possible (though unlikely) that they changed the clutch but set the free play wrong and the clutch is being held partially disengaged.

If you don't feel any free play then you should try adjusting the clutch linkage. On the left side of the tractor forward of the clutch pedal you'll see a rod that's threaded on both ends with nuts. It connects the pedal with a rod sticking out of the transmission. Break the nuts loose (one of them is going to be left hand threaded) and twist the rod to change it's effective length. Lengthen the rod to increase the free play. You want around 10-15% of the pedal's travel to be free play.

 

[Minerboyd]

Exactly. The clutch allows you to disconnect the hydrostatic transmission so you can shift the range transmission and the PTO (though I think that can be engaged on the fly).

Well I'd make sure the free play is set correctly first. Push on the clutch pedal. You should feel it travel a short distance without much resistance and then have heavier resistance for the rest of the travel. What you're feeling is the throw out bearing engaging the clutch fingers. Ideally the pedal will have about 1/2 to 3/4 of an inch of travel before the bearing touches the clutch fingers. It's possible (though unlikely) that they changed the clutch but set the free play wrong and the clutch is being held partially disengaged.

If you don't feel any free play then you should try adjusting the clutch linkage. On the left side of the tractor forward of the clutch pedal you'll see a rod that's threaded on both ends with nuts. It connects the pedal with a rod sticking out of the transmission. Break the nuts loose (one of them is going to be left hand threaded) and twist the rod to change it's effective length. Lengthen the rod to increase the free play. You want around 10-15% of the pedal's travel to be free play.

I checked the free play on the clutch and it had about 1" of free play before engaging. Since this was originally reported I have changed the Super UDT Fluid and both transmission filters. I was noticing that the longer the tractor was used the less power I could get to the wheels. The Dealer that sold it to me said they thought it sounded like an old or dirty filter. After changing it I actually had no improvement. Now it barely moves in any gear.

I don't have any PTO implements to test but I am now almost definitely convinced that the clutch is gone and that no amount of adjusting it will help. I am just really frustrated since the dealer assured us that everything had been checked out and was in good working order. I would bet we have used it for less than 20 total hours since we bought it in March 2013 and we are now looking at $250.00 hauling fee just to get it back to the dealer to get it checked out and another $250 to bring it back once it has been repaired, and who knows what they will charge me for the new clutch and possibly flywheel.

 

[North Idaho Wolfman]

Minerboyd,
Replacing the clutch is not that hard of a job, if you have a good flat spot or garage and a few normal metric tools, floor jack and a couple jack stands, it can be done in a day.
There are plenty of people on here that can help you get threw it, and save a ton.

 

[Minerboyd]

After several weeks in the shop, it turned out to be a problem with the Hydrostatic Transmission which had gone bad. The dealership that sold it to us had assured us that everything was in good working order so when they found out that the hydrostatic transmission was not working correctly and since we had reported problems within the first 30 days o owning it they offered to rebuild it for the cost of the parts only. We got it back with a rebuilt HST for around $1400. which I assume is a decent price for a fully rebuilt HST.

Thank you for everyone that offered suggestions and ideas on how and what ot test to find out what was causing it but in the end it turned out to be a much bigger problem than I or anyone else had expected.