B7100 HST Low power. Cause?

[998cc]

A little history. My dad loved gardening and used a TroyBilt roto-tiller until he just couldn't manage it anymore. He then bought a B7100HST package from a rental yard; it included a front loader, box scraper, FL850 rotary tiller and RCR48 mower attachment. The B7100HST had been neglected/abused during its rental life and needed a complete engine rebuild. Dad was a very competent mechanic and happily took it on. I was involved with the rebuild and know he installed new sleeves, pistons, rings bearings, etc. The machine work was done by Del's machine shop in Sacramento. He likely put about 200-300 hours on the tractor after the rebuild.

Fast forward. I inherited the 7100 and attachments in 2013 and have been using mostly for maintaining a road on my property. It seemed to be suffering from low power in both high and low range but was adequate for the road work and roto-tilling. This week, I decided to service the mowing attachment and put it to use; the mower is in pretty good mechanical condition only requiring a little work on the wheel adjusters and all around lube. Problem: The tractor can barely spin up the mower on high PTO speed; trying to move forward will slow it down considerably. It is usable on low PTO speed as long as the grass in no more than about 8 inches tall and using a very slow forward speed. I assume this is not normal. Otherwise, the engine starts easily and runs well, and the fuel is new. Any thoughts on a possible cause/solution?

Thanks folks.

 

[ptsg]

Does the engine bog down as well? Or the mower just slows down along with the drive speed?

If the engine bogs down, then it could be fuel related. If not, then it could be the clutch slipping. Even though it's an HST, it still has a dry clutch to engage and disengage the PTO, however, the input shaft that powers the PTO, also powers the HST, so if the clutch splits, it will affect both PTO and drive.

There is a Workshop manual of this site if you don't have one already. It may help you some. Here is the link: Index of Kubotabooks/Tractor Owners Manuals/

 

[rScotty]

About every one of those older Bs and compact tractors from that era need that cleanable trans/hydraulic screen cleaned in the transmission case, and also a new fuel filter.
Both of those filters need frequent replacement and both will cause it to slow down. The symptom will be that it will start and runs OK at low rpm, but when you try to get up and go - or use more power - or go uphill ..... it will just bog down.

I think that model had a cleanable filter in the transmission. Take a look at the service manual, and if so, be sure to take it out and clean the screen so that your HST doesn't starve for fluid. Taking out the screen will dump all the trans/hydraulic oil so when you do it, replace the spin-on filter as well if it has one... and I think it does. Since the oil is lost, replace that as well with new good quality trans/hydraulic oil yes, that oil is expensive. so be prepared.

BTW, good trans/hydraulic oil is clear. If yours is looking murky or milky it has water contamination - very common in that model. If so, that's another reason to clean the screen filter.

And while you are doing filters, do the fuel filter as well. It's the other thing that will cause your tractorto start and run ok at low rpm as I said....but bog when you advance the throttle.
good luck,
rScotty

 

[998cc]

About every one of those older Bs and compact tractors from that era need that cleanable trans/hydraulic screen cleaned in the transmission case, and also a new fuel filter.
Both of those filters need frequent replacement and both will cause it to slow down. The symptom will be that it will start and runs OK at low rpm, but when you try to get up and go - or use more power - or go uphill ..... it will just bog down.

I think that model had a cleanable filter in the transmission. Take a look at the service manual, and if so, be sure to take it out and clean the screen so that your HST doesn't starve for fluid. Taking out the screen will dump all the trans/hydraulic oil so when you do it, replace the spin-on filter as well if it has one... and I think it does. Since the oil is lost, replace that as well with new good quality trans/hydraulic oil yes, that oil is expensive. so be prepared.

BTW, good trans/hydraulic oil is clear. If yours is looking murky or milky it has water contamination - very common in that model. If so, that's another reason to clean the screen filter.

And while you are doing filters, do the fuel filter as well. It's the other thing that will cause your tractorto start and run ok at low rpm as I said....but bog when you advance the throttle.
good luck,
rScotty

rScotty. That describes the problem pretty well. Bogging down when going uphill is a symptom. I do have the manual for the tractor and will look into it tonight.
Best regards.

 

[998cc]

Does the engine bog down as well? Or the mower just slows down along with the drive speed?

If the engine bogs down, then it could be fuel related. If not, then it could be the clutch slipping. Even though it's an HST, it still has a dry clutch to engage and disengage the PTO, however, the input shaft that powers the PTO, also powers the HST, so if the clutch splits, it will affect both PTO and drive.

There is a Workshop manual of this site if you don't have one already. It may help you some. Here is the link: Index of Kubotabooks/Tractor Owners Manuals/

I agree that fuel may be an issue. Replacing the fuel filter this week. Clutch is not slipping as far as I can tell. It just bogs down (speed and mower jointly). I do have the manual for it.
Best regards.

 

[rScotty]

rScotty. That describes the problem pretty well. Bogging down when going uphill is a symptom. I do have the manual for the tractor and will look into it tonight.
Best regards.

I checked at the online parts using Messick's excellent website:
Messicks | Your home for New Holland, Case IH, Kubota & More.... I order all my parts from them.

Yes, the B7100 HST has both a cleanable screen (below) and a spin on disposable can type filter for the oil in the common sump used by the tractor's hydraulics and HST transmission. Replacing the spin on and cleaning the other will involve new oil there. (UDT or SUDT type)

You also have a replaceable fuel filter. Replacing that will require bleeding the fuel system - which can be frustrating the first time you do it and is simple the second time around. But messy both times.

Those are most likely to be the cause of your problems. But even if they are not, any mechanic is going to require replacing them before looking deeper.
rScotty

 

[998cc]

I checked at the online parts using Messick's excellent website:
Messicks | Your home for New Holland, Case IH, Kubota & More.... I order all my parts from them.

Yes, the B7100 HST has both a cleanable screen (below) and a spin on disposable can type filter for the oil in the common sump used by the tractor's hydraulics and HST transmission. Replacing the spin on and cleaning the other will involve new oil there. (UDT or SUDT type)

You also have a replaceable fuel filter. Replacing that will require bleeding the fuel system - which can be frustrating the first time you do it and is simple the second time around. But messy both times.

Those are most likely to be the cause of your problems. But even if they are not, any mechanic is going to require replacing them before looking deeper.
rScotty

View attachment 737374

I never knew there was a replaceable filter under that cover! Messicks was very helpful. I ordered all of the filters, o-rings and 4 gals of genuine Kubota Super UDT oil. If the problem is in the filter/screens, this should fix it. No worries bleeding the fuel system; between my old Ford 4000 diesel tractor and this Kubota, I have done it many times since the 1970's. 998cc

 

[998cc]

First off, thank you all for your advice.

I cleaned the screens and reinstalled with new O-rings. (The large screen was coated with gunk while the smaller one was fairly clean.) Installed a new Kubota Hydraulic oil filter and a Kubota fuel filter then new Super UDT2 oil. The old oil was murky and needed to be changed. After a few short runs and topping off the hydraulic oil in between runs, the oil level is now normal. No leaks.

The test:
The tractor has a little more pep than before; however, it still lacks enough power use the mower on high PTO. The mower is a little better on low PTO than before.
I was hoping for a better outcome but do have a higher comfort level in the tractor knowing the work has been done. It was well worth doing.

Thanks.
998cc

 

[Jerry/MT]

First off, thank you all for your advice.

I cleaned the screens and reinstalled with new O-rings. (The large screen was coated with gunk while the smaller one was fairly clean.) Installed a new Kubota Hydraulic oil filter and a Kubota fuel filter then new Super UDT2 oil. The old oil was murky and needed to be changed. After a few short runs and topping off the hydraulic oil in between runs, the oil level is now normal. No leaks.

The test:
The tractor has a little more pep than before; however, it still lacks enough power use the mower on high PTO. The mower is a little better on low PTO than before.
I was hoping for a better outcome but do have a higher comfort level in the tractor knowing the work has been done. It was well worth doing.

Thanks.
998cc

Check your fuel flow at the outlet from the fuel filter. Or better yet at the inlet to the injector pump (IP). It should gush out. If it dribbles or is intermittent, there are other areas that can restrict the fuel flow rather than just the fuel filter. The tank outlet, the line from the tank to the filter, the filter head passages, line to the IP. Line could be pinched, etc. If this is an older tractor then I would suspect the tank has crud in it. Some of these tanks have a screen at the outlet that can be clogged.

 

[SDT]

First off, thank you all for your advice.

I cleaned the screens and reinstalled with new O-rings. (The large screen was coated with gunk while the smaller one was fairly clean.) Installed a new Kubota Hydraulic oil filter and a Kubota fuel filter then new Super UDT2 oil. The old oil was murky and needed to be changed. After a few short runs and topping off the hydraulic oil in between runs, the oil level is now normal. No leaks.

The test:
The tractor has a little more pep than before; however, it still lacks enough power use the mower on high PTO. The mower is a little better on low PTO than before.
I was hoping for a better outcome but do have a higher comfort level in the tractor knowing the work has been done. It was well worth doing.

Thanks.
998cc

Assuming that you have serviced/replaced the air filter, sounds like a compression test is in order.

SDT