Kubota B21 TLB complete driveline rebuild

[dfkrug]

I came across this 1998 Kubota B21 TLB this summer, and I bought it as
an interesting repair project. It was owned by a small water company, which
took good care of it, having frequent maintenance done at the Kubota dealer.
It seems to have been stored inside and greased frequently. This tractor has
about all the options the buyer could get from the dealer: a 4-in-1 FEL bucket
with front auxilliary hyd valve. Factory work lights on the FOPS. A triple-spool
rear aux hyd valve block, also factory. The 4-in-1 is only about 510 lb and not
made by Kubota or any known 3rd party. It has some wear and tear, but it
seems quite servicable.

The tractor experienced transmission problems, so it went to the dealer for
repair back in the spring. The dealer cracked the tractor and gave the owner
the bad news....my guess is more than $10,000 for repairs. Instead they
sold the owner a new tractor, taking this machine in trade. The dealer re-assembled
enough to get it rolling, then sent it off to an auction yard. They left out and
"lost" many of the important internals, including gears, shafts, and various
misc pieces. This is a mechanic's nightmare. The missing parts and how they
go together would need to be deduced from the cryptic parts diagrams and
the marginal factory service manual. I like a challenge.

Following are the steps I took to disassemble, analyze, buy parts, and re-assemble.

First photo is how the tractor arrived, off the trailer. I also filled the bed
of my PU truck with parts.

Next: further dissassembly

 

[dfkrug]

This is the so-called main frame (or main flame, as it is called in
the parts book).

The main frame weighs just a bit less than 200#, but seems to
be designed to maximize the rigidity of the b/h mount. 1.5"
pins, too. This style of subframe is what I used to model my
custom subframes after.

The second photo shows that the upper pin does seem to get a
bit of wiggle.

 

[dfkrug]

Cracked.

Note the steel "mid-frame" that connects the clutch housing to the
main transmission.

Other things unlike other CUTs I have worked on or seen include
a separate centrally-mounted hydraulic oil tank, already removed.

The cowling (front section of the hood) is 1/8" steel plate!

 

[ultrarunner]

I've been looking at the B21's for sale and so far the prices have been what I consider rather high unless it is for a well worn rental yard unit.

Interesting project... I hope you were able to buy it right and keep posting!

 

[machmeter62]

There is another gentleman on this board that faced similar problems with a B-21 that he purchased from a rental yard. The HST went "Tango/Uniform" shortly after the sale, even though the HST had been rebuilt prior to the sale?

He totally dismantled the tractor, and showed step-by-step, the rebuilding of the HST an other issues, which included many detailed photos of critical parts of the HST, that may have been overlooked on the prior rebuild?

His project was about a year ago, or less, and you may want to do a search; he is very talented with attention to details too!

 

[dfkrug]

This is a shot under the rear half of the tractor. Note the cast axle
housing extensions that support the ROPS. The 8 bolts that hold the
ROPS to this part of the rear easily collect debris and get rusty. This
tractor was well cared for and not left out, but the bolts probably had
less than half their original strength left. Note the new grade 8 bolt in
the second photo. If your tractor supports its ROPS this way, your
bolts could be seriously compromised, too.

 

[dfkrug]

I've been looking at the B21's for sale and so far the prices have been what I consider rather high unless it is for a well worn rental yard unit.

A rental B21 just went up for sale last week nearby. $15.3K, I think it was.
Rental is a hard life, and my first tractors were all rentals. This one has
2350 hr, but looks WAY better than rental units with 1/3 the hours and years.
I was very attracted to the 4-in-1 also. More on that later.

Also, a nearer rental yard has a newish B21, which I have looked at a few
times to see where certain parts go, exp the many many hyd hard lines.
My unit is together and working now, but I have a couple of left over parts.
Hmmmm.

 

[dfkrug]

There is another gentleman on this board that faced similar problems with a B-21 that he purchased from a rental yard. The HST went "Tango/Uniform" shortly after the sale, even though the HST had been rebuilt prior to the sale?

He totally dismantled the tractor, and showed step-by-step, the rebuilding of the HST an other issues, which included many detailed photos of critical parts of the HST, that may have been overlooked on the prior rebuild?

His project was about a year ago, or less, and you may want to do a search; he is very talented with attention to details too!

Thanks for mentioning that. I found it.....OCT 06. I don't know how it got
by me.....

He had broken ring/pinion in the rear diff. I had that, too, but I get ahead
of myself.....

 

[dfkrug]

When I got the tractor, the clutch friction disk, press plate, and
flywheel were together in a box, and filthy with dirt and oil. When
I pulled them apart, I found my first major problem.

A closeup of the friction disk shows that the male splines have been
turned into sharp teeth. The clutch had become oil contaminated,
big time. So my working theory was that seal between the clutch and
primary gear box had failed, causing oil to get into the forward part
of the clutch housing. BTW, this also means that the trans input
shaft was also toast, as can be seen if you look closely at the splines.

This spline shaft shows one of the 3 bevel gears that comprise the
primary trans, which seems to serve only to lower the main drive shaft.
It increases speed by a ratio of 1.15. Because the gears are beveled
(for noise reduction I assume), the horribly chattering clutch served to
put excessive end thrust on one of the gears, distorting one of the spacers.
I am glad I checked for that.

As for my working theory of failure, it was wrong. The engine crank seal
had failed, dumping oil onto the clutch. Now I wonder if this violently
chattering clutch somehow precipitated the broken gears I had in the
main gearbox?

 

[EddieWalker]

Interersting project!!!!

Thanks for all the details and pics. There's allot that you are doing that I've never seen before, nor do I really want to attempt, so it's realy nice to see what you're doing.

I doubt this will help, but when the transmission went out on my jeep, I pulled it out to have it rebuilt, and found out that it was cheaper to just buy a brand new one to replace the old one. Faster too!!

Eddie

 

[machmeter62]

DAVE: When you get that industrial strength TLB back together; it should draw a lot of attention, if you trailer it anywhere with that 4n1 bucket? If you ever decide to sell it, it may draw a ransom price also!?

My adjacent neighbor has had one for several years, and I am amazed at it's capability....no 4n1 bucket however! Which I think is very rare too?

I have the B21's big brother the L35, and also have the 1/8" (boiler plate on the hood),... small rocks, etc. just bounce off! I like the manueverability of this generation of Kubotas, and their strength/ability to work in confined quarters. I still think Kubota should have painted them yellow?

You are making good progress on the rebuild, and enjoy the progress reports/photos too!
LEE

 

[dfkrug]

I doubt this will help, but when the transmission went out on my jeep, I pulled it out to have it rebuilt, and found out that it was cheaper to just buy a brand new one to replace the old one. Faster too!!

But, Eddie, half the fun is doing it yourself! And, since I work for "free"
on my own stuff, I am way ahead on costs.

Thanks

 

[dfkrug]

I have the B21's big brother the L35, and also have the 1/8" (boiler plate on the hood),... small rocks, etc. just bounce off! I like the manueverability of this generation of Kubotas, and their strength/ability to work in confined quarters. I still think Kubota should have painted them yellow?

Thx, Lee.

One of the reasons I got this machine is I wanted to see first hand what
some of the differences are betw regular CUTs and industrial CUTs.

Not only do I see 1/8" plate on the cowl, but also excellent undercarriage
armor, a throttle that is accessible while working the hoe, a complex
seat rotation mechanism, fairly hi hyd flow, triple filtration of hyd oil, etc.

 

[dfkrug]

OK, now for the fun part.

One of the reasons I was interested in this tractor is to take apart
a modern HST. The good news here is that the HST is OK, and needs
nothing. There is a separate filter for the HST, which protected it from
the puree of broken metal fragments that came out of the main gearbox
and rear end.

First photo shows the main components of the HST. The motor and the
pump are virtually identical. The pump varies its displacement with
a variable angle swash plate. The motor uses a fixed swash plate.
The tube with the O-rings in the middle is where the MFWD drive shaft
passes thru the HST on its way to the main gearbox. Oil in the HST
does not mix with that in the gearboxes until after filtration. Nice.

2nd photo shows the cylinder block and pistons. Note the hole in the
brass "slipper", that rubs against the swash plate. That supplied lube
to the plate, and, of course, contributes to some of the inefficiencies
of a HST.

Finally, I miked everything and nothing was out of spec. One bit of
good news. I replaced the main shaft ball bearings anyway (they are
cheap).

Next: charge pump and main gearbox

 

[machmeter62]

OK, now for the fun part.

One of the reasons I was interested in this tractor is to take apart
a modern HST. The good news here is that the HST is OK, and needs
nothing. There is a separate filter for the HST, which protected it from
the puree of broken metal fragments that came out of the main gearbox
and rear end.

First photo shows the main components of the HST. The motor and the
pump are virtually identical. The pump varies its displacement with
a variable angle swash plate. The motor uses a fixed swash plate.
The tube with the O-rings in the middle is where the MFWD drive shaft
passes thru the HST on its way to the main gearbox. Oil in the HST
does not mix with that in the gearboxes until after filtration. Nice.

2nd photo shows the cylinder block and pistons. Note the hole in the
brass "slipper", that rubs against the swash plate. That supplied lube
to the plate, and, of course, contributes to some of the inefficiencies
of a HST.

Finally, I miked everything and nothing was out of spec. One bit of
good news. I replaced the main shaft ball bearings anyway (they are
cheap).

Next: charge pump and main gearbox

DAVE: I really enjoy your posts and pictures of the inter-workings of that B21. It is beyond my skill level, and too many parts would be leftover!

My skill level was challenged with my first car, a '40 Chev. coupe, which had a vacuum shift for synchronizing the gears, which was soon inoperative! I had to learn to "double clutch" it, that often got the attention of pedestrians, with verbal comments of "grind me a few pounds" till I found the solution!
LEE

 

[dfkrug]

This post gets into the charge pump, which supplies hyd fluid to the suction
side of the HST pump, and the implement pump.

The charge pump (first pic) is mounted to the front of the HST and is always
driven at engine speed by the drive shaft, even when the HST has no demand
(foot off the go pedal). This takes up a few hp, further sapping some of the
engine power seen by the PTO, even when the tractor is not moving. Looking
at the pump, I saw scoring of the aluminum case, and the steel rotary gears.
This can be attributed to the fact that this pump draws oil from the reservoir thru
a steel mesh screen, which did not completely exclude the metal particles that
got into the oil from the disintegrated main gearbox. The charge pump only
operates at a couple hundred psi, and this one may suffice, but I was not
comfortable re-using it. Another $300 for a new pump.

The second pic is a little blurry, but it shows the implement pump, which I
opened up to check. It is in fine condition, thanks to good filtration. The
diverter valve sends oil to the power steering valve, and excess oil (when not
steering) supplements the flow from the charge pump to the HST. The HST's
oil from the charge pump is filtered again, explaining the lack of damage to the
HST. In the past with older cars, I liked to open up the engine oil pumps to
check for scoring, which gave me some indication of how well the previous
owner(s) cared for the car.

Next: look, Ma, no gears!

 

[rtdiggr]

interesting project, i look forward to the progress.
Shane

 

[dfkrug]

Here is the main gearbox just after I separated it from the HST, and
the rear diff housing. Nothing inside but one gear, one shaft, and one of
the 4 shifter forks!

2nd photo is the inside of the diff housing. Pinion gear and shaft are
missing, but the damaged ring gear is in there.

3rd photo shows some of the loose broken pieces I found. The circlip
and steel casting fragment were inside the hyd oil reservoir, also in the
picture. The new steel casting forms a bearing and shaft support
inside the gearbox. Some huge forces shattered the original. Most
interesting was the crushed spring, which came from the MFWD shifter
detent. I found it at the bottom of the diff housing, behind the largest
axle gear. I think it got crushed between the ring and pinion gears, shattering
their teeth. If so, what caused the spring to come out? Perhaps a
broken shifter fork, as that one is only aluminum, and the operator could
have forced it.

 

[yubby]

Dave,

Been there done that. Looks like you are making good progress on the rebuild.

It is interesting to note that we are both in Norcal (I am in Ovale), too bad our B21's didn't break down around the same time.. Could have compared notes.

So far my b21 is running solid after the rear-diff rebuild (about 60 hours).

Just make sure you get the HST pedal return spring on before you put it all back together (I forgot and had it all back together before realizing).

Cheers -Lucas

 

[dfkrug]

Been there done that. Looks like you are making good progress on the rebuild.

It is interesting to note that we are both in Norcal (I am in Ovale), too bad our B21's didn't break down around the same time.. Could have compared notes.

So far my b21 is running solid after the rear-diff rebuild (about 60 hours).

Just make sure you get the HST pedal return spring on before you put it all back together (I forgot and had it all back together before realizing).

Hey Lucas....

I missed your B21 thread the first time around, but I read it all as soon as
MACHMETER pointed it out. I am glad nothing has broken since.

It is true that there were some assembly order issues for me as I did not
take the tractor apart first. I had some trouble with the HST pedal spring,
but not the one you had. I had to fabricate the part on the HST casting
as it was one of my missing parts. I DID make the mistake of putting the
2 halves of the tractor together before attaching the top hyd hard line to the
charge pump. This would not have happened if I had taken the tractor
apart myself.

Were your ROPS/FOPS support bolts on the rear axle as bad as mine?