336D 4WD front-rear mechanical ratio?

[TX mower]

Does anyone know the 4WD Mechanical Ratio for the Yanmar 336D?

This for the purpose of using the lead/lag calculator here to assist in selecting replacement front tires.

By 'reverse engineering' based on the OEM tire specs it seems to be in the range of ~1.60 to ~1.68 but small differences in either the Mechanical Ratio or the tire's spec Rolling Circumference have a big impact on lead/lag when trying to stay in the desired 2%-5% range (closer to 2% but not below preferred), so would like to know the true exact Mechanical Ratio if possible.

Thanks in Advance!

 

[normde2001]

Why is this an issue? Merely replace with same size tire or measure front/rear rolling circumference and divide front by rear.

 

[winston1]

I don't have one, but know from the ones I do have, the original repair manual will have that information in it. I know there are some out there with that manual, maybe they will respond to you. I am quite aware that manufacturers of the same size tires often have different rolling circumferences. I don't blame you for being a bit picky. My several years of experience with the 4 wheel drives leads me to believe it is pretty important if you use the 4 wheel drive with regularity.

 

[TX mower]

I don't have one, but know from the ones I do have, the original repair manual will have that information in it. .....

winston1, Thanks for prompting a third dig through my original Service (repair) Manual where I finally found the info needed:

"Front Axle-to-Rear Axle Speed Ratio: 1.6945 to 1"

Also found the 336D-specific (rather than generic rule-of-thumb) lead spec:

"Front Wheel Pre-Run Percent: Spec 1 to 4%; Wear Limit 0 and 6%"

Also appreciate your understanding of my 'picky-ness' .... I've owned this tractor for ~27 years (second owner) and I believe one reason it's been a reliable workhorse (which I have every reason to expect to continue) is that I try to give it proper PM. It bears the scars of a life of real work but is mechanically and functionally 100% solid.

My 336D is equipped (as sold new to the first owner) with the Yanmar YFL-1500 loader and 67"-wide Yanmar YMB 1-85 heavy-duty box blade with drop-down rippers. Both get frequent use in 4WD. I have every interest in ensuring proper care of my 4WD drivetrain and it's continued reliability.

Gotta mention that the 336D Automatic Draft Control is simply superb with that box blade - I end up doing a lot of gratis driveway maintenance for my neighbors who have tractors lacking that feature which makes the job so much easier and quicker with better finished results.

The last time I had to replace tires the OEM Bridgestones were still available, not the case now, and as you pointed out research reveals a fair amount of difference in rolling circumference among brands even for the same size and basic R1 style.

So yeah, I'm being picky about tire replacement and don't consider that an "issue", just prudent.

 

[winston1]

winston1, Thanks for prompting a third dig through my original Service (repair) Manual where I finally found the info needed:

"Front Axle-to-Rear Axle Speed Ratio: 1.6945 to 1"

Also found the 336D-specific (rather than generic rule-of-thumb) lead spec:

"Front Wheel Pre-Run Percent: Spec 1 to 4%; Wear Limit 0 and 6%"

Also appreciate your understanding of my 'picky-ness' .... I've owned this tractor for ~27 years (second owner) and I believe one reason it's been a reliable workhorse (which I have every reason to expect to continue) is that I try to give it proper PM. It bears the scars of a life of real work but is mechanically and functionally 100% solid.

My 336D is equipped (as sold new to the first owner) with the Yanmar YFL-1500 loader and 67"-wide Yanmar YMB 1-85 heavy-duty box blade with drop-down rippers. Both get frequent use in 4WD. I have every interest in ensuring proper care of my 4WD drivetrain and it's continued reliability.

Gotta mention that the 336D Automatic Draft Control is simply superb with that box blade - I end up doing a lot of gratis driveway maintenance for my neighbors who have tractors lacking that feature which makes the job so much easier and quicker with better finished results.

The last time I had to replace tires the OEM Bridgestones were still available, not the case now, and as you pointed out research reveals a fair amount of difference in rolling circumference among brands even for the same size and basic R1 style.

So yeah, I'm being picky about tire replacement and don't consider that an "issue", just prudent.

Well said. :thumbsup:

 

[rScotty]

Does anyone know the 4WD Mechanical Ratio for the Yanmar 336D?

This for the purpose of using the lead/lag calculator here to assist in selecting replacement front tires.

By 'reverse engineering' based on the OEM tire specs it seems to be in the range of ~1.60 to ~1.68 but small differences in either the Mechanical Ratio or the tire's spec Rolling Circumference have a big impact on lead/lag when trying to stay in the desired 2%-5% range (closer to 2% but not below preferred), so would like to know the true exact Mechanical Ratio if possible.

Thanks in Advance!

I used to have a YM336D and measured that internal gear ratio when I went to turf tires. This may not be arithmatically exact, but to three places the internal ratio is 1.694:1.000.
I haven't used the calculator that you posted as a link. I always did my own measurements. Be sure to use rolling circumference; the shape of a loaded tire is not circular.
Good luck with your project.
rScotty

 

[TX mower]

For anyone interested, perhaps this table will be helpful when shopping for tires:

Just a quick bit of fun with Excel

FWIW per Mr. Steven Sawyer, Sr. Project Engineer at Firestone Ag Tires (successor to Bridgestone Ag in the USA), the specs for the discontinued OEM Bridgestones that came on my 336D when new were:
Front – 8.0-16 Bridgestone Farm Service Lug M, (R1), 6 ply, 1330lbs@35psi max, 6x16 rim, RC:92”
Rear – 12.4/11-28 Bridgestone Farm Service Lug M, (R1), 4 ply, 2216lbs@17psi max, 11x28 rim, RC:147”

^That particular OEM combination would yield a calculated Lead of 6.05%

(not 'obsessing' - just a retired engineer having fun with numbers, it's what we do )

 

[rScotty]

For anyone interested, perhaps this table will be helpful when shopping for tires:

Just a quick bit of fun with Excel


FWIW per Mr. Steven Sawyer, Sr. Project Engineer at Firestone Ag Tires (successor to Bridgestone Ag in the USA), the specs for the discontinued OEM Bridgestones that came on my 336D when new were:
Front 8.0-16 Bridgestone Farm Service Lug M, (R1), 6 ply, 1330lbs@35psi max, 6x16 rim, RC:92
Rear 12.4/11-28 Bridgestone Farm Service Lug M, (R1), 4 ply, 2216lbs@17psi max, 11x28 rim, RC:147

^That particular OEM combination would yield a calculated Lead of 6.05%

(not 'obsessing' - just a retired engineer having fun with numbers, it's what we do )

Wow!, that's not only mighty impressive useof Excel.... but it actually looks to be useful info, too.
I'm going to go look at the original tires for my old YM336D and see how they fit the chart.
Sure wish I could use Excel that well.
rScotty

 

[rScotty]

Wow!, that's not only mighty impressive useof Excel.... but it actually looks to be useful info, too.
I'm going to go look at the original tires for my old YM336D and see how they fit the chart.
Sure wish I could use Excel that well.
rScotty

After 500 hours over 10 years, here is what my YM336D measured with the stock tires. Visually the tires didn't show much wear.
The stock tires on my YM336D were Ag tread (R1). Front is OHTSU 4 ply 8x16 Traction Field and Road which is an 8" wide tire on a 6" wide 16" rim. Rolling Circumference measured 90.4 inches at 20 psi.
Rear is a Firestone, also Traction Field and Road 13.6x26 6 ply with is on a 12" wide 26" rim. Rolling circumference measured 147 inches at 22 psi.

Although these tires are different size OEM from the OEM on TX mower's YM336D, my front to rear internal gear ratio is the same: 1.695:1

So by the chart that gave minea stock lead ratio of around 4.28%.

Going to turf tires some few years later required different rims and different tires. Having my choice of ratios to end up with, I chose to make the tire ratio match the internal gearing pretty nearly exactly. Well, I say "nearly exactly", but there wasn't a significant % difference. Real close to 0% lead. The tractor worked fine that way and steered well too - so my guess is that the real ratio was just ever so slightly postitive. The only oddity was with that new 0% lead setup it could then be shifted between 2WD and 4WD at any speed and on the go without a lurch or a grind. In fact, the weight of the 4WD lever would cause it to shift into and out of 4wd going over bumps. It's possible that Yanmar uses a little lead-induced torque "wind up" on the FWD shaft to keep it in gear. I added a hook to keep the 4wd lever from moving on its own.
rScotty

 

[TX mower]

^Cool, Thanks for sharing that info!