B7610 sudden loss of forward / reverse power

[Ideehoan]

My mid 90s B7610 has been a 100% faithful workhorse for 20 years. I don't know it's hours as the meter reads 600.7 and that can't be right assuming the last digit is 10ths. I never pay attention to it, just do annual oil changes. Today it lost forward and reverse power. It will move on flat ground but will not climb a slight hill in forward or reverse even in low range.
Hydraulic fluid level is OK. Hydraulic power on the loader seems OK lifts front of machine easily. It had been functioning normally when I parked it a few days ago so I'm baffled.

I suspect the hydrostatic drive may have failed. Very bad timing as we are about to move and I have heavy items I would normally use the loader for.

I would appreciate any ideas for troubleshooting.

 

[jonsstihl]

the old hours meters were on a cable and 1 hr was at PTO rpm. An hour at idle would not amount to 1 hr on the meter. I think those models have a screen on the hydraulic system as well as the filters. did that get cleaned out at the last hydraulic fluid change. perhaps its a clutch issue. I'm pretty sure the hydraulic system only supplies the pre charge pressure to the system and the transmission creates its high pressure internally.

 

[Carl_NH]

Check all the linkages from the shift lever to the transmission case - there are several connections - one may have come loose. Hope it's something this simple.

 

[Ideehoan]

I just had the notion to check in 4wd as I was roading it in 2WD this morning when the trouble started. Well in 4WD I have normal drive power. Most of my work is in 4WD and I'm not sure how long since I used 2WD.
So I assume my hydrostatics are fine and the problem is with the rear diff. It's narrowed down but I'm still baffled at what can cause partial power to the rear diff. I have a foot pedal for diff lock. I assume there's a clutch in the diff?

(I did crawl under and saw nothing amiss.)

 

[Carl_NH]

Hmm this is odd - there is no clutch in the Diff and the diff lock should not change - you might try the diff lock when in 2WD and see if that makes a difference - that might give you some idea if its gear related.

For what its worth I run in 2WD most of the time and use 4WD only as needed and on gravel or grass.

 

[Ideehoan]

It just occurred to me to check 2WD function with the diff lock engaged. I have power again with the diff lock on!
So it seems the most likely failure is a broken axle shaft.
Not sure how these come apart but I'm about to find out.

 

[Ideehoan]

Looking online not finding a downloadable service manual.
Can anyone help with that? Looking for the process to change an axle.

 

[Carl_NH]

Here's a link to Messicks - on line parts diagrams - best I can do but gives you some idea of what you are dealing with, Kubota B7610HSD (Hydrostatic Transmission, 4wd) Parts Diagrams

 

[Carl_NH]

Also might try brake turning - meaning engage the RH brake, and LH brake independently to see if they both stop the wheel. This I believe is in the upper part of the case conneting to the wheel stub shaft.

Kubota B7610HSD (Hydrostatic Transmission, 4wd) Parts Diagrams

Kubota Parts Catalog Lookup. Buy Kubota Parts Online & Save!

www.messicks.com

 

[oldnslo]

Stupid question but is one of the rear tires spinning on the rim? Take a piece of chalk or paint marker and mark both tires vs valve stem. Drive around in 2 wd to see if orientation changes on one of the tires.

Sounds silly but this does happen.

 

[Ideehoan]

I have the R axle off. Geared arrangement with the diff lock. All seems normal.
The L wheel is off and feels normal.
The wheels/tires are so heavy they must have fluid and the R one is leaking a bit around the rim.

oldnslo may have hit the nail on the head with his "stupid" but brilliant question?

 

[Ideehoan]

I think oldnslo may have hit the nail on the head with his not so "stupid" brilliant question!
Just went and looked closer at the tires. I noted they are super heavy taking them off. I didn't know they were fluid filled when I bought it. There's a few drops of purple fluid leaking from the tire bead on one. Maybe beet juice?
That tire has zero PSI!!
Did not look low on air.
OK I'm an idiot for not checking pressure but I'm 99% sure that's it so I'm a happy idiot.
I can put it together in 20 minutes. It was due for a fluid and filter change anyway.

I think oldnslo just saved my bacon. Thanks to all who replied and especially oldnslo who is not so slo after all.

 

[Carl_NH]

Awesome - Old Onslo gets the prize for proper diagnosis! And the leaking fluid would cause the slippage.

Yes they are very heavy filled with fluid - 250-300Lbs maybe? And changing the Hyd fluid, access to the strainer and filters are much easier with the left rear wheel off on my machine.

 

[ning]

epic TBN win!

 

[oldnslo]

I hope the slipping tire on rim is the problem since easy fix.

I will be the first to admit that it would not be my first thought on why tractor suddenly won’t move…

 

[Ideehoan]

Re-posting, replied earlier but maybe didn't hit send.

I think you saved my bacon oldnslo. I pulled the R axle - nothing bad. Checking L with wheel off also seems ok.
I noticed taking the wheels off they are obviously filled and noticed a little drip of colored fluid from the tire bead.
Could not get a pressure reading due to stuck valve but with valve removal it's definitely low.

So I put the axle back on, waiting for sealant to dry. Replaced the tire valve, put in 40 psi and will test the theory shortly.

Very thankful for the help here. Perhaps oldnslo is really not so slow!

 

[Ideehoan]

Problem solved!

I was having serious thoughts of removing the differential - no small job.
I can only imagine doing that and being stumped - nightmare.

oldnslo really did save the day - my deepest gratitude!

 

[oldnslo]

Glad to help and thanks for letting us know what the solution was.

 

[Little Red Tractor]

Old age and treachery will overcome youth and skill...almost every time! Oldnslo for the win!

 

[jonsstihl]

thanks for updating the thread. it is nice that it was a simple solution too bad you already had the axle out by the time you figured it out. must by industrial tires the carcass is so stiff it doesn't go flat even at 0 PSI.