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