L2500DT: fixing front wheel drive

[pigdoc]

Hi Folks,

Just a quick note for now, I'll follow-up this evening with more detail.

I have found a reason for the front wheel drive to be nonfunctional on this tractor - the front coupler on the propeller shaft was completely stripped out. Apparently, this is not uncommon. $250 later, I got all the parts I needed (including a new prop shaft) at Messick's yesterday.

While I had the prop shaft off, I took a good look at the drive pinion in the front axle. It has about 20 degrees of rotational 'slop' in it (rotates when tractor not moving). It looks like someone had (over)filled the front axle with motor oil, not UDT as recommended in the operator's manual. I figure whoever did that knew that the ring/pinion were wasted, and just wanted to put something cheap in there to keep the bearings lubed. I drained a small amount out of the center section for a peek. It was nice and clear, yellowish like motor oil is, not dirty at all, but there was steel shavings in it. Not a lot, but enough to notice.

So, I'm NOT inclined to just install the new prop shaft and forget about it.

Right now, I need a scan of the WSM pages that cover the front axle drive pinion set-up: mesh and preload.
If I'm lucky, the preload is out of adjustment (but, don't know how that could have occurred...).

I'll do some more investigation this afternoon, including draining all the oil out of the front axle.

Also the splines on the end of the drive pinion that engage the prop shaft coupler are worn. Not horribly, but enough to allow the shaft to wobble. Not good.

I have a sinking feeling that I'll be installing new ring and pinion gears, if not the entire differential.

Anybody have DT front axle for earlier L-series for sale?
This one is all cast-iron (no tube stock), and it has "L2250" cast into the back side of the right end.

The drive pinion and prop shaft are both 20mm (major diameter), 14 splines.

More later,
Thanks,
-Paul

 

[pigdoc]

More detail.

First thing I did was check the transmission fluid (UDT). It was a brownish, milky color, so I just drained everything (about 12 quarts). While I was at it, I pulled the screen. It was about half covered with gray snot. I wiped that off with a paper towel and soaked it in Purple Power. After a few minutes, I wiped that off, and soaked it again. Rinsed it under hot water, and it came out clean as a whistle.

There is a procedure for R&Ring the propeller shaft on Youtube that gives some perspective on the task:
How to fix Kubota 4X4 drive coupling. - YouTube

However, with my tractor, I found it easier to just unbolt the Front Wheel Drive case at the bottom of the transmission (4 bolts) and pull the entire prop shaft assembly. I could not get the two-piece shaft cover to telescope enough to access the couplers, let alone drive the split pins out from underneath! Besides, I had already drained the trans fluid. I could tell someone had been in there before - gray silicone sealer slopped on the Front Wheel Drive case gasket.

The propeller shaft on this tractor is super long - 80cm, and heavy - 3kg with the couplers. Seems like a lot of potential for inertia to be an issue if there is any wobble. [If I was designing this shaft installation, I would have supported it with a pillow block at both ends.]

Looking at the drive pinion in the front axle again, there does not seem to be any sideplay or endplay in it. It just has that rotational slop in it. Somebody please tell me that's normal! This diff is engineered very similar to a Chrysler 8-3/4 or a Ford 9-inch. There are 11 bolts/studs holding the 'chunk' into the housing. Uses shims under the pinion bearings to adjust pinion depth. Pretty standard stuff. The side-to-side location of the ring gear is adjusted by a shim against the R bearing cap, and an adjuster threaded into the L bearing cap.

I'm not intimidated by rebuilding and setting up the diff, I'm just not looking forward to all the heavy lifting to get it out of there! Looks like I'll have to pull the bevel gear housings that create the drop down to the front wheels, so that I can pull the axle shafts out of the diff. Once the diff is out of the axle case, I can rebuild it on the benchtop.

I just spent about an hour surfing Messick's parts diagrams, and it looks like about every 25-30hp Kubota L-series tractor from 1985-2000 used the same ring gear and pinion (31353-99120). I found 10 models in all:

1985-1992: L2250 - L2550 - L2850
1989-1991: L2050
1991-1993: L2650 - L2950
1991-1998: L2350
1998-2000: L2500
2000-2003: L2600 - L3000

Doesn't seem likely that I'll find a parts tractor that's not suffering the same wear. Yesterday, I spent about an hour in the parts tractor lot at Wenger's (of Myerstown). I spotted about 30 Kubota back-halves, but not a single DT front axle, anywhere. That tells you something, I guess.

I don't relish the idea of shelling out $750 for a new ring gear and drive pinion, but if that's my only option...And then, there are the differential side gears ($200) and pinion gears ($150) that are probably also roached if the drive pinion is bad.

I wondered, if I drained the oil out of the front axle, could I get a bore scope up through the drainhole close enough to inspect the gear teeth? I half-expect to be able to shove my little finger up the drain hole and find a loose gear tooth laying there, on the bottom of the axle case.

I once shelled a ring gear behind a 300hp V8 during a launch. was a 3.91 ratio. Tore 5 teeth off the ring gear, all next to each other. I figured it a cracked tooth that caused it to fail.

Any ideas welcome!

I'm going to be using front-wheel drive a LOT, so I need to make it right.

[Sorry, I don't have any pics. I can't get them off my phone and into my emailbox right now.]
But, that youtube video is pretty much exactly what I saw, except my prop shaft was also toasted.

-Paul

 

[pigdoc]

Well, today I stuck a borescope in the oil drain hole of the front axle and got a GOOD look at about 10 of the ring gear teeth. They all look absolutely perfect. So, I'm NOT going to rebuild the differential. Yay!!!

Plus, I could look at the borescope screen while turning the drive pinion, and see that there is very little, if any lash between it and the ring gear. That 20 degrees of rotational slop is happening in the bevel gear housings at the outer ends of the axle shafts. I can actually hear the gears clanking out there when I turn the drive pinion back and forth. That's a good indication to be CAREFUL when shifting from forward to reverse when in 4WD so that I'm not hammering those bevel gears.

So, I'm going to bolt everything back together and fill 'er up with oil!

The splines on the drive pinion are moderately worn, from the old coupler slipping on them.
Could use some advice on how (or whether) to bed the front prop shaft coupler on the drive pinion. Was thinking a few strips of steel shim stock, just to eliminate any slop in the splines. Had thought of JB Weld, but it probably won't stand up to the pressure between the splines. Both? I'll be able to complete the installation well before the JB Weld sets up, so alignment shouldn't be a concern.

I'm just trying to save the splines on the drive pinion for a later day (a MUCH later day!) and eliminate any wracking that will hammer on the splines.

The coupler can be jammed onto the drive pinion tight, because to remove the prop shaft next time, I'll do it like I did this time - just drop the front drive housing and pull everything out together. The front coupler can just stay jammed onto the drive pinion.

I think I'll delete the prop shaft cover. I can see that it would serve the purpose of preventing grass and weeds from winding around the prop shaft, but I don't have any ground like that here! Besides, the new shaft does not have a back cut for the cover seal where the two halves meet, anyway.

Last night, I replaced the lever for the FEL control valve and the bushing it swivels in. The old bushing was VERY worn and fussy to remove. The new bushing needed to be reamed after I pressed it in with a C-clamp, but I got it fitting the shaft on the lever perfectly. MUCH better!

Seat tracks and adjuster are VERY rusty. I got the assembly out, but the pin that the seat brackets ride on when the seat tilts forward on is frozen solid into its bore. I'll put a torch on it to see if I can loosen it up and drive it out. It needs to be replaced anyway. And the holes in the brackets that ride on that pin are wallered out pretty bad. I think what I'll do is get a new Kubota pin, and then find a couple of steel bushings that will fit on it. Then, I can drill out the wallered holes to fit the OD of the bushings and weld them to the brackets. That will provide a much larger wear surface.

I thought the rollers for the seat track were innovative. Just 4 short lengths of coiled spring, laying on their sides to serve as rollers. Probably better than ball bearings, because they ride in a mild-steel track. The load needs to be spread out a bit...

Got a new aftermarket seat in the mail this week. Was $120, including shipping. Made in Turkey. Not an identical replacement - plastic structure rather than steel. But, it looks to be very well made. Bolt holes match up - that's always a plus! I'll follow up with a report after I install it. But, gotta deal with those brackets first. No more sitting on a wet sponge!

-Paul

 

[pigdoc]

Did some more cogitating on how to deal with the badly worn splines on the front axle drive pinion.

The engineers had in mind that you'd telescope the two-piece shaft cover to access the couplers at each end, then punch out the spring pins that center the couplers, and then just slide (retract) the couplers towards the middle of the prop shaft, letting the prop shaft drop straight down. Simple....IF you don't have an FEL support in the way!!!

Again, when I took mine apart, rather than fight the stuck shaft cover and the close fit of the FEL support, and try to drive those split pins out while laying on my back, I just dropped the Front Wheel Drive case and pulled the prop shaft out towards the rear of the tractor as an assembly. Worked slick as snot.
That's the only way I'll ever do it again.
That's the only way I'll ever do it again.

HEY, so then the couplers do not need to be retractable! That means I can make them longer, allowing the added coupler length to engage unused spline area on the transmission output drive, the front drive pinion, AND the prop shaft itself!!! Looks like the added length will engage another 8 mm of unused spline area on the trans output shaft:

...and on the front axle drive pinion:

NASTY, huh?
That slipping coupler must have acted like a grinder on those splines... Because, any time the front wheels are turning, that drive pinion is spinning. Notice how well the shaft cover was protecting BOTH shafts from moisture <cough>. That's the old o-ring still there in the inside of the axle casting.

I mean, duh, the prop shaft is going to get warm, just from heat gain from the groove in the engine oil pan that it passes through. What happens when you shut the tractor off and the air inside the shaft cover cools off again? Condensation! You gotta let them puppies BREATH!

The unused spline length is between the red lines. It's not much, but I'll take what I can get! I'll grind out the split pin holes in the coupler large enough to plug-weld it solidly to the front drive pinion in two places (see image below). Given how trashed the splines are on that front drive pinion, there's no need to try to save their integrity. I'll complete the reassembly before making that weld, so that the coupler is perfectly aligned with the pinion. Utilizing that unused spline area will help align everything.

For the trans output shaft, I think I'll drill up through the split pin hole in the coupler to make a small (3-4mm) divot in the shaft. Then, I'll drive the split pin into that divot in the shaft to prevent the coupler from sliding on the trans output shaft.

By pinning the coupler to the trans shaft and welding the coupler the front drive pinion, the couplers will not slide out of place and then the prop shaft itself can just float between the couplers.

To get the added coupler length, I'm just going to get another NOS coupler, cut it in half, and buttweld each half to another NOS coupler. My son is a professional welder - he'll probably want to TiG the coupler pieces together.

It's curious that the engineers tried to make it um, *convenient* to remove the prop shaft. Just what were they anticipating? On the other hand, it seems somewhat unusual for industrial engineers, in the design, to actually facilitate replacement of parts that are prone to failure. {That should be part of the "right to repair" laws.]

Here's a pic to illustrate the surplus spline length on the prop shaft:

That hole is for the split pin, which is supposed to go across the coupler between the shaft ends to locate the coupler.

Badda-BING!!!
-Paul

 

[North Idaho Wolfman]

I've seen much greater wear on pinion splines.
I would just throw new couplings on it and call it good.

You can change the shims on the bevel cases to tighten up the gear slop on them.

 

[Henro]

How did you determine it was motor oil and not 80W90 gear oil which is an acceptable substitute for UDT in the front axle?

 

[pigdoc]

How did you determine it was motor oil and not 80W90 gear oil which is an acceptable substitute for UDT in the front axle?

Thanks Henro,
When I wrote that it was motor oil, I had only drained out a couple of tablespoons, so I was just guessing. When I drained the rest (just over a gallon), and poured it off, it was obvious that it was 80W90 gear oil. It was still very clean, so I just put it back in, leaving the very small amount of steel shavings sticking to the bottom of the drain pan.
-Paul

 

[pigdoc]

I've seen much greater wear on pinion splines.
I would just throw new couplings on it and call it good.

Thanks for your reply Wolfman.
Ya, I was tempted to do just what you suggest. But, I measured the true sideplay between a NEW coupler and the drive pinion - more than 0.020". And, it's just going to get worse. And, I'm going to seriously test that connection with the work I have planned for this tractor. If I strip the rest of the splines off that drive pinion, it's game over. The odd thing is that, the wear is worse on the top half of the shaft, the splines you can't see in the image.

When you're in 4WD and the tires are losing and then gaining traction, there's going to be a helluva lot of wracking at the prop shaft couplers. So, the way I'm going to use the tractor, the problem is going to get worse...FAST, if I'm not aggressive about fixing it. I do NOT want to see this thing fail again in the middle of January! I can tell that it's going to be useless to try to push snow without 4WD. Need some rear wheel weights, too!

You can change the shims on the bevel cases to tighten up the gear slop on them.

That's good to know!
It's another big job, but something I'll have to put on my to-do list. Seems like the R side is worse than the L. Now, if you'll excuse me, I'm going to go shop a WSM...

Thanks,
-Paul

 

[pigdoc]

Finished the repair.
Cut a 13mm long section from a new prop shaft coupler.
Then, TiG welded it to another coupler. This added length to cover unused splines on the front drive pinion.
Here's a pic of the welded coupler:

You can see how I beveled the ends of the splines in the coupler to ease installation with a die grinder.

Welder son strongly advised against any attempt to weld on the shaft, as weld would be brittle, and just crack. So, I backed off to the less invasive fix, and continued.

Then, I disconnected one end of the tie rod, to give me better access to the drive pinion.
Hit it hard with a wire wheel on my angle grinder to polish it:

Sprayed everything down with Brak-leen.
Then, I slathered the drive pinion splines with JB Weld, used almost a teaspoon.
Tapped the coupler into place, and then installed the shaft, the other coupler, and the front wheel drive case. Gave the whole thing a few spins (with one front wheel off the ground) to align everything. Then, let it set for a day-and-a-half.

Test drove it in 4WD today, very cautiously, on a loose surface, and it looks like it will hold. If it doesn't, I can always try something else!

-Paul