B7100 HST Diff lock does not seem to be working

[Whit]

I am a recent owner of the B7100 HST.
I have checked the diff lock works on jack stands. When I push the diff lock in both the rear wheels turn and cant be held back with you hands, so it seems the diff lock is working. However when I have been mowing on a slope and get one rear wheel spinning, I press the diff lock in and even though the pedal goes all the way down to the place where it seems to lock in. Only one wheel spins still.
Steps for this.
One rear wheel spins
Stop accelerating, brake.
Push diff lock in,
accelerate
One rear wheel spins.

I can see from the parts diagram there is sort of a clutch with a spring that engages the splines. All I can think of is one of these parts is warn? So even though I cant hold the wheels back with my hands on the jack stands out in the field there is a lot more pressure? There is never any grinding nosies.

Or am I not engaging the diff lock correctly?

I am thinking I need to take the rear right side cover off to check the condition of differential lock parts out? To do this do I need to drain the hydraulic fluid and can the hydraulic fluid be reused?

What do you guys think?

 

[TheOldHokie]

I am a recent owner of the B7100 HST.
I have checked the diff lock works on jack stands. When I push the diff lock in both the rear wheels turn and cant be held back with you hands, so it seems the diff lock is working. However when I have been mowing on a slope and get one rear wheel spinning, I press the diff lock in and even though the pedal goes all the way down to the place where it seems to lock in. Only one wheel spins still.
Steps for this.
One rear wheel spins
Stop accelerating, brake.
Push diff lock in,
accelerate
One rear wheel spins.

I can see from the parts diagram there is sort of a clutch with a spring that engages the splines. All I can think of is one of these parts is warn? So even though I cant hold the wheels back with my hands on the jack stands out in the field there is a lot more pressure? There is never any grinding nosies.

Or am I not engaging the diff lock correctly?

I am thinking I need to take the rear right side cover off to check the condition of differential lock parts out? To do this do I need to drain the hydraulic fluid and can the hydraulic fluid be reused?

What do you guys think?

Assuming its the same as the B7200 the lock is a dog clutch with two square keys. IIRC the spring holds the clutch apart and the pedal overcomes the spring and engages the clutch. The square edges of the keys can get worn off and slip under load. On my tractor that produced noise and a pulsing feel in the pedal. Not a horrible job to replace the clutch.

Dan

 

[Henro]

Not sure if it applies to your tractor, but I have read here that one is not supposed to engage the diff lock when a wheel is spinning. At least on small tractors like the B series.

MAYBE OK if the wheel is slipping very slowly?

Suggest you find a manual that explains how to use the diff lock on your tractor properly...whatever "properly" might be...

 

[Whit]

Assuming its the same as the B7200 the lock is a dog clutch with two square keys. IIRC the spring holds the clutch apart and the pedal overcomes the spring and engages the clutch. The square edges of the keys can get worn off and slip under load. On my tractor that produced noise and a pulsing feel in the pedal. Not a horrible job to replace the clutch.

Dan

View attachment 86714

Yes that looks to be the same. When you replaced it did you have to drain the hydraulic fluid?

 

[TheOldHokie]

Yes that looks to be the same. When you replaced it did you have to drain the hydraulic fluid?

1. The drawing is the B7100 parts breakdown.
2. You are opening up the differential case so you must drain the oil.
3. IIRC the dogs engage the differential carrier and on mine the carrier was still in good shape. If yours is not the cost goes way up.

Dan

 

[Whit]

1. The drawing is the B7100 parts breakdown.
2. You are opening up the differential case so you must drain the oil.
3. IIRC the dogs engage the differential carrier and on mine the carrier was still in good shape. If yours is not the cost goes way up.

Dan

Thanks Dan, sorry I missed that it was the B7100. Is there anything else I should check while I have the diff oil drained? I am guessing I cant re use the oil?

 

[TheOldHokie]

Thanks Dan, sorry I missed that it was the B7100. Is there anything else I should check while I have the diff oil drained? I am guessing I cant re use the oil?

Oil is pretty cheap

Dan

 

[PoTreeBoy]

Thanks Dan, sorry I missed that it was the B7100. Is there anything else I should check while I have the diff oil drained? I am guessing I cant re use the oil?

If it's less than, say, half way to the next change, I'd say reuse it. Make sure you use a clean/dry pan and clean around the plug so you don't drop dirt in it. Then filter through clean/dry cloth when refilling.

I think you have a suction screen, no filter. You should definitely pull and clean it.

 

[Whit]

Oil is pretty cheap

Dan

I guess it is all relative, the B7100 HST takes 3.6 gallons or 13.6 litres of Kubota UDT hydraulic oil, that is about $80USD or $120AUD

 

[Whit]

If it's less than, say, half way to the next change, I'd say reuse it. Make sure you use a clean/dry pan and clean around the plug so you don't drop dirt in it. Then filter through clean/dry cloth when refilling.

I think you have a suction screen, no filter. You should definitely pull and clean it.

Thanks for the tips

 

[hodge]

If at all possible, do not engage the diff lock with a wheel spinning. That is when excessive wear or breakage happens. It is seldom that the dogs are lined up when the lock is engaged, so the wheel should be rotated as slowly as possible, until it engages. Slipping in is much different than shock engaging.
It's possible that the previous owner of your tractor had misused the diff lock.

 

[Whit]

I drained the hydraulic fluid (as it needs changing anyway) I removed the rear right axel from watching this video

This was the hydraulic oil that came out. Does it look normal?

I noticed sludge build up in the axel case corners, I am guessing it is throughout other areas of the machine. How do you flush and clean the hydraulic system?

The teeth on the dog clutch on the diff case look slightly worn down on one side, I hoping this is not causing my diff lock not working problem as it looks like the diff case would need to be replaced?

The side with the spring looks like it is not worn at all.

The only other thing that I found was the mechanism that engages the diff lock was a little rusted, it is also cast and not smooth which I found strange. The shaft was a little rusted and pitted. I cleaned the best I could.

I am yet to put back together to see if the diff lock will work. What do you guys think? Will I need to replace the diff case with the warn dog teeth?

 

[TheOldHokie]

I drained the hydraulic fluid (as it needs changing anyway) I removed the rear right axel from watching this video

This was the hydraulic oil that came out. Does it look normal?
View attachment 88201

I noticed sludge build up in the axel case corners, I am guessing it is throughout other areas of the machine. How do you flush and clean the hydraulic system?
View attachment 88194

The teeth on the dog clutch on the diff case look slightly worn down on one side, I hoping this is not causing my diff lock not working problem as it looks like the diff case would need to be replaced?

View attachment 88195

View attachment 88196

The side with the spring looks like it is not worn at all.
View attachment 88197
View attachment 88198

The only other thing that I found was the mechanism that engages the diff lock was a little rusted, it is also cast and not smooth which I found strange. The shaft was a little rusted and pitted. I cleaned the best I could.
View attachment 88199
View attachment 88200

I am yet to put back together to see if the diff lock will work. What do you guys think? Will I need to replace the diff case with the warn dog teeth?

Hate to say it but I think your problem is that damage to the differential carrier. Good news is its only $260.

Dan

 

[Russell King]

The fluid looks like it is loaded with water and your tractor may be leaking water into the transmission case through the shifters or somewhere else if it was stored outside

 

[Whit]

I think/hope I have fixed the diff lock issue.
I put the rear right back together and did a full services. Replacing all fluids and filters.

The diff lock pedal had about 25mm of free play before lever on rear right was engaged. Pedal was also hitting the mid mound mower hanger bracket.
Figured out lever on rear right was only moving 15mm. The service manual with the 3 parts seems to suggest it needs to be 23mm.
The adjuster rod was already maxed out, so I moved the lever position from pointing straight up vertically, to one spline position to the rear, this allowed me to adjust the rod out so there was no play in the pedal. The lever was now moving about 23mm and the pedal was just touching the mid mound mower hanger when fully pressed.
Photo showing new diff lock lever position.

I only had a change to do a quick test but it seemed to work more consistently in forward and reverse. I had the tractor at the bottom of a steep slope, slowly went up one rear wheel would spin almost instantly. Took foot off forward pedal, pressed diff lock pressed forward pedal both wheels would spin, took foot off forward pedal and then diff lock pedal. Pressed the forward pedal, one rear wheel would spin. I tried this a couple of times in forward and reverse and seemed to work as expected.

I am hoping that the issue was the dog clutch was not engaging all the way in and that is what rounded the corners of the diff housing side, and that there is still enough left on it when it is fully engaged.
I will test again when I have more time.

 

[Whit]

I think/hope I have fixed the diff lock issue.
I put the rear right back together and did a full services. Replacing all fluids and filters.

The diff lock pedal had about 25mm of free play before lever on rear right was engaged. Pedal was also hitting the mid mound mower hanger bracket.
Figured out lever on rear right was only moving 15mm. The service manual with the 3 parts seems to suggest it needs to be 23mm.
The adjuster rod was already maxed out, so I moved the lever position from pointing straight up vertically, to one spline position to the rear, this allowed me to adjust the rod out so there was no play in the pedal. The lever was now moving about 23mm and the pedal was just touching the mid mound mower hanger when fully pressed.
Photo showing new diff lock lever position.
View attachment 88599

I only had a change to do a quick test but it seemed to work more consistently in forward and reverse. I had the tractor at the bottom of a steep slope, slowly went up one rear wheel would spin almost instantly. Took foot off forward pedal, pressed diff lock pressed forward pedal both wheels would spin, took foot off forward pedal and then diff lock pedal. Pressed the forward pedal, one rear wheel would spin. I tried this a couple of times in forward and reverse and seemed to work as expected.

I am hoping that the issue was the dog clutch was not engaging all the way in and that is what rounded the corners of the diff housing side, and that there is still enough left on it when it is fully engaged.
I will test again when I have more time.

This fixed my diff lock issue. Works as expected now.

 

[Geezer3d]

Glad that you got this working with minimal expense. And thank you for following up to let us know what solved the problem.

I am surprised that the diff. housing side wore so much more than the other side of the clutch. I wonder if maybe that part has been replaced at some point before you bought the tractor.

 

[Whit]

Glad that you got this working with minimal expense. And thank you for following up to let us know what solved the problem.

I am surprised that the diff. housing side wore so much more than the other side of the clutch. I wonder if maybe that part has been replaced at some point before you bought the tractor.

You could be right as there was some different looking bolts when I pulled it apart.