Yanmar YM1510D – Front Wheel Assist Not Working

bmaverick · Saturday at 5:53 PM

YanmarMatt said:
Update:

Thanks again, everyone, for all your help so far. It’s been reassuring to know that I can ask questions here and get such thoughtful advice.

I was working on my tractor again today and wanted to share what I’ve found:

I removed the left axle cover to check for stripped gears—so far, nothing looks destroyed in there.

I pulled the driveshaft, and the lower U-joint looks a bit scuffed up. It’s not completely broken, but I think I’ll go ahead and replace it.

One thing I’m still debating: On the front differential, where the driveshaft connects—if I spin that input gear, I would expect the axle spindles to turn. However, they’re not.

Looking behind the left plate, I can see a gear spinning, so something is moving internally.

My main question now: Is there some sort of clutch or mechanism in the front differential that engages the wheels? If so, I’d like to understand how it’s supposed to work so I can troubleshoot more effectively.

So far, I’m encouraged not to have found any completely destroyed gears—just the chippedView attachment 3884820 View attachment 3884821 View attachment 3884822 gear I posted about earlier and the U-joint that needs replacing. If anyone can help me identify how this front differential functions, I’d really appreciate it.

Thanks again for all the guidance.

— Matthew

Like this,

YanmarMatt · Saturday at 5:57 PM

I originally thought I could buy the U joint replacements from brand M parts, but it looks like it’s just some of the components. The part that looks worn on mine is the part that attaches to the input drive for the front differential. I don’t know if replacing those roll pins would help. On that input drive it looked like it was a slotted for a key however the U joint didn’t seem to match that key. I don’t know if the key portion would’ve got worn off, either way the input drive is not spinning the axle drives as I would have expected.

bmaverick · Saturday at 5:58 PM

winston1 · 2025-08-10T06:55:44-0400

Long video but might be worth your time.

bmaverick · 2025-08-10T10:51:50-0400

winston1 said:
Long video but might be worth your time.

Winston, amazing video, thanks for posting. This goes into all kinds of details for the 4WD system. I learned a bunch from this, even though I have 2WD.

Yanmar made the system rather easy, not difficult.

Oz_Kioti · 2025-08-10T18:05:56-0400

Agree 100%. Good clear and STEADY video, good audio, and a great presenter, and well worth my time to enjoy watching. Well done Dr.

YanmarMatt · 2025-08-10T18:29:46-0400

Thanks again for all the help so far—it’s been a huge benefit having this forum to turn to.

We spent more time on the tractor and ended up tearing into the front differential. The good news: we found no damage at all to the gears inside. That’s encouraging.

What seems to be the underlying issue is that the roll pin (shear pin) on the lower U-joint may have been the problem all along. I’ll be replacing that. You can see the sheared pin and before and after.

I was surprised that the roll pin is carrying all that torque to those front wheels, but I suppose an engineer was thinking let’s make the fail point be a cheap piece to replace and easy to access (little did that engineer know I’d still rip apart the entire tractor!!

)

Reassembly & Oil Questions

Oil flow for U-joint & driveshaft
- I know how to get oil into the lower differential, but how do I get oil into the U-joint with its housing?
- For the upper U-joint and housing—does that oil also flow down the driveshaft? Or is it isolated?
Gear oil
- What oil do you recommend for the gears in this model? Any specific type/weight?
Gaskets
- For reassembly, should I order new gaskets (do they even exist) or just make my own?
- If making my own, what gasket material works best here?
- Should I use any silicone or sealant in addition to the gasket material? If so, what type?

I’ll try to post a couple of photos of the roll pin area and the U-joint in case that helps confirm what I’m seeing.

Thanks again for all your help—this has been a great learning experience so far.

Also, in the previous post, I mentioned that the input drive for the gearbox would spin but the axle wouldn’t spin. Turns out the reason for that is because I had the left axle hub off, which presses the differential gear into the helix gear. Just thought you guys would get a good laugh out of that bit of user error.

Thanks again for all the guidance—this has been a great learning experience so far. I’ll order some new parts and hope to have a concluding post in 2 weeks or so.

gengine · 2025-08-10T18:37:59-0400

Where Yanmar makes a lot of the smaller John Deere tractors, if you have a Yanmar part number, most likely the JD dealer can cross reference the part numbers and get one out of their warehouses. Your gonna pay more for it, but a parked tractor isn't worth much. I have crossed several JD parts to Yanmar parts to buy cheaper, but if the cheaper isn't available, then I had to suck it up and buy the JD part.

careyo63 · 2025-08-10T18:38:22-0400

YanmarMatt said:
Thanks again for all the help so far—it’s been a huge benefit having this forum to turn to.

We spent more time on the tractor and ended up tearing into the front differential. The good news: we found no damage at all to the gears inside. That’s encouraging.

What seems to be the underlying issue is that the roll pin (shear pin) on the lower U-joint may have been the problem all along. I’ll be replacing that. You can see the sheared pin and before and after.
View attachment 3885664 View attachment 3885665 View attachment 3885666

I was surprised that the roll pin is carrying all that torque to those front wheels, but I suppose an engineer was thinking let’s make the fail point be a cheap piece to replace and easy to access (little did that engineer know I’d still rip apart the entire tractor!! )

Reassembly & Oil Questions

Oil flow for U-joint & driveshaft

I know how to get oil into the lower differential, but how do I get oil into the U-joint with its housing?

For the upper U-joint and housing—does that oil also flow down the driveshaft? Or is it isolated?

Gear oil

What oil do you recommend for the gears in this model? Any specific type/weight?

Gaskets

For reassembly, should I order new gaskets (do they even exist) or just make my own?

If making my own, what gasket material works best here?

Should I use any silicone or sealant in addition to the gasket material? If so, what type?

I’ll try to post a couple of photos of the roll pin area and the U-joint in case that helps confirm what I’m seeing.

Thanks again for all your help—this has been a great learning experience so far.

Also, in the previous post, I mentioned that the input drive for the gearbox would spin but the axle wouldn’t spin. Turns out the reason for that is because I had the left axle hub off, which presses the differential gear into the helix gear. Just thought you guys would get a good laugh out of that bit of user error.

Thanks again for all the guidance—this has been a great learning experience so far. I’ll order some new parts and hope to have a concluding post in 2 weeks or so.

My overrun clutch is setup with a pin and hard to see or get to for that matter. You have to line the outside to the Pin on the PTO.. My FM 95% of the time so never have to remove it! If I did it would be spring loaded so I could remove it easy. Old and new if I was going to remove it. The Yanmar RS1400 Tiller you couldn't use either. Yanmar PTO shaft was way to long. BTDT...

bmaverick · 2025-08-10T22:45:16-0400

YanmarMatt said:
Gear oil

What oil do you recommend for the gears in this model? Any specific type/weight?

Some use oil and some use grease. The manuals call for the old school GL4 80W90.

Unless you have a time machine, GL4 is a rare thing to find anymore. And GL5 is not all that great.
What you can do, upgrade to 75W90 synthetic. Shop around for a good deal.

Example,