Kubota B7610 Hydro Behavior

[kcoburn]

I recently bought a used B7610 with about 300 hours. It's equipped with a loader and MMM. The hydrostat will occasionally "upshift", without moving the pedal, as though it was an automatic transmission selecting the next higher gear. The ground speed will increase slightly, maybe 5%. I also have an L5240 with hydro and have never experienced anything similar with it. Is this a "normal" behavior or should I be concerned about "impending doom" ?
An unrelated question. The PTO shaft cover has a hole for a bolt to retain it, but I don't have the bolt. My guess is it's a 6MM about 1/2" long. I've tried a standard 6mm.It will turn about 1 1/2 turns, then starts to hang up. Either there's a nick in the threads in the hole, or it's a different thread count. I'll bet any of the B7--- models have the same PTO shaft cover. Would anyone happen to know the bolt size before I run a 6mm tap into the hole and bung up the threads?

 

[HEC]

I would want to know if and when the filters and hyd. oil were changed . Things don't sound normal to me , but I am new to the hydrostat tranny .

 

[k0ua]

Never had a hydro "upshift or lurch by itself". Hate to say it but that does not sound good. Easy stuff first like fluid and filters.

 

[kcoburn]

The dealer where I bought it says all fluids and filters were changed at 255 hrs

 

[kcoburn]

As I think about it, I wonder if they cleaned the strainer. It could be "starving" the hydro a little, then clearing up causing the surge. Does that make sense?

 

[Tractorrr]

Do the Rpm's jump up when it "up shifts"? Have you checked the fuel filter and air filter? That's what I would start with. Try to fix/ check the simple things first. I also agree with it possibly being a strainer issue.

 

[DennisArrow]

I have a B7610 with perhaps 900 hours on it now. LOTS of bucket, loader, and blade work.....LOTS.......NO that is NOT a normal situation. Please answer all the questions above to help us.
I think, even though the dealer did it, a fluid and filter change would be worth it for sure. Using the CORRECT Kubota recommended filters and fluid. I also go along with KCOBURN's suggestion above. Something is going on for sure. Dealers make mistakes, so that is the first place to start. What does the former owner have to say???

By the way, the factory advises 90W or SUD2 in the front end/hubs. SUD2 weeped out around a couple of knuckle seals. Changed over to 90W and any leakage is gone............. God bless.......Dennis

 

[Tractorrr]

As far as the bolt size, it should be metric I would think. If you could just buy some bolts of 6mm with different size thread pitches and see which one fits. Or, you might also be able to actually order that specific bolt by looking it up on an illustrated parts list from either the KUBOTA or Messick's website

 

[kcoburn]

Parts breakdown doesn't show the bolt, just the plastic cover itself. I'll take your suggestion and see if I can find a couple of 6mm bolts with different pitches.

 

[kcoburn]

I bought the tractor from the dealer and they're reluctant to hook me up with the former owner. I'm going to check with them to confirm that they did clean the strainer when they changed fluid. I hate to dump and replace it with only 30-40 hours on it. It's a lot of work, dropping the deck, etc. And it'll be over $100 for the Super UDT2 and filter.
Thanks for the " heads- up" on the gear oil vs UDT in the front gear case oil. I did that on my L5240. This B7610 was already changed over to gear oil.

 

[rswyan]

We have a B2910 that has roughly 1700 hours, bought new from the dealer ... it has done the surging thing for as far back as I can recall ... probably since very shortly after it was new.

I always assumed that it was something inherent in the design.

 

[kcoburn]

rswyn,
Thanks. I was hoping to hear someone say something like that. I ran the tractor 4 hrs yesterday and it didn't surge at all. I'm still going to follow up to get confirmation that the suction strainer was cleaned.

 

[Egon]

Do the engine rpm's increase when ground speed goes up?

 

[kcoburn]

Egon, No, I don't think they RPM's change, though I've never been watching the tach when it happens. The "pitch" of the engine increases slightly and the ground speed increases as though it's found another slightly higher "gear". The change in engine "pitch" is probably because it's working a little harder maintaining the RPMs in this higher "gear".

 

[Egon]

Only other thing I could add are the foot pedals and linkage free and move easily. Will it happen on both smooth and rough terrain? ie can the seat movement effect your pedal contact? If you have cruise control will it do it then?

Just questions; no solutions!

 

[kcoburn]

Egon, Thanks for sticking with me on this. I just greased the hydro pedal pivot before I last used the machine. That may explain why I ran it for 4 hrs without incident. I'm comforted by the "rswyn"s response above stating that he has experienced "surge" since his machine was nearly new. The seat is locked so tight, it won't move when I try. I've never used "cruise" so I don't know if it happens then. I'm going to just use it, as is, unless it starts acting up again.

 

[duber34]

I had a 2004 B7610 for about 9 years and 450hrs. It would surge/ lurch from new when I was trying to maintain a constant ground speed while mowing in high range. I never had the problem when I began to mow in low range. In high I depressed the pedal roughly 1/3 and in low I could just about keep it floored to maintain a ground speed that provided a quality cut. (RPM's constant for both scenarios) I assumed it was me being a bonehead by cutting in high. My reasoning was I wasn't allowing proper hydro flow with the pedal only depressed 1/3.

Regards,
Duber

 

[rswyan]

Do the engine rpm's increase when ground speed goes up?

From what I recall in our case I don't believe that they do.

 

[duber34]

Same here. RPM's stayed constant through the lurch.

Regards,
Duber

 

[chim]

Does it do the jerk when you are headed uphill? I had a B7500 that did, and someone on here explained there was something in the hydro locking up to eliminate some slip. It was normal. That tractor had over 1000 hours on it when I sold it three years ago and never had any problems with the trans.

I don't think the L3200 does it, but after spending 10 years on the B7500 I may have become so accustomed to it / subconsciously expecting it that it doesn't even register if it happens.