OC-12 outer pinion gears


I am taking my diff apart and having trouble getting the outer pinion gears off.
I have loosened the nut and put a gear puller on it but they would not budge.

I suspect I may need a better gear puller and o try harder, but wanted to ask if there is anything else retaining them besides the nut.

Also, how much end play should the pinion gears have? I don't see that in the manual.
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Snowy Rivers

Well-known member
These bad boys are on a shaft with a taper.
Loosen the nut enough to give clearance between the nut and the GEAR
Get the puller on the gear...pressing on the nut end.....USE A PLATE TO PROTECT THE SHAFT.

Tighten the hell out of the puller with an impact wrench....Smack the puller end where you had the rattle wrench.....THEY WILL POP LOOSE

Now...use a die grinder and a bur/stone and mark the tooth that lines up with the keyway in the shaft.
Mark each pinion as to where it was in the case and mark the gears too....these parts have been running in these places a while and will be happier if you put them all back in the same place.

Same thing when you break the compensator apart....mark everything so it all goes back the same.

Be sure the dowel pins go in snug and are peened so they can't wiggle out.

The gears MUST be timed ( keyway or marked gear tooth faces out...A straight line from center of diffy through the center of the small pinion shaft and the center of the keyway)
Line up all 3 before you try to install the drum/gear.....If these are not timed they can bind up....

Book is specific on this.

Another tid bit.

These gear teeth start chewing into the case over time as well as the thrust washers.
Debur the teeth with a dies grinder....Replace the washers with fresh hard ones...FASTENAL CARRIES ONES THAT WILL WORK.

The crappy shim washers they used SUCK.....
I machined the inner case to use standard thrust washers from a couple different auto trannies.

Go into the van cat thread and read all the material on my diffy build.
Lots of pics and data.
It fixed a lot of issues

The rear diify stuff of use starts a post #524 and goes from there


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I read your thread and have those the thrust washers on order.
I am going to look for a different puller. I am using one of those 2/3 jaw puller sin 2 jaw configuration and when I get it really tight it wants to tilt.

Snowy Rivers

Well-known member
The thrust washers ???? For the pinions ??? or the ones for the case and the drum ???

The inner ones require the case to be machined...
Having machine tools makes life good.


I ordered the case and drum washers and will have a local shop do it. If I was in lower 48 I might just send it to someone, but shipping something that heavy from AK will be cost prohibitive.
I will order the pinion washers after I get it open and make sure nothing else is wrong.

I returned the 5 ton puller and got a 7 ton puller. It worked on 3 so I flipped the diff over to go after the ones on the ring side and found the jaws are too big to get under the gears. Maybe I need to try the smaller one again, or a different style of puller?


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Snowy Rivers

Well-known member
These can be a beotch.

I wrapped an old sweatshirt around that bad boy to make sure CHIT did not fly off and give me a fat lip


My friend who is the co-owner got back in town and brought over a puller he had that worked perfect.
Now we are unsure how to get the compensator apart.
I can see someone has done some grinding around the pins, but the current state is better described as "mangled" rather than peened.
I guess tonight's task will be to go after them with a die grinder.


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Snowy Rivers

Well-known member
Do not grind them
Mark the halves of the compensator so it can go back the same way
Take the bolts out
The pins will slip out from between the halves when you tap it apart
The mess in the holes is to keep the pins in place
Somebody just got a bit overzealous on getting this apart
The pins will stay in one side or the other of the compensator
The peening will be there for you when you slide it back together and bolt it up
Look the compensator over for marks on the halves
There should be some
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I have marked the compensator pieces with a punch so I can put them back in same orientation.
I tried beating them apart with a deadblow and nothing budged. Is it supposed to be easy or hard to get apart?


I used a bigger hammer and got it apart. The pins seem to the hold up. They were a very tight fit.
1 pin even stuck to the inner compensator instead of the outer half.

It looks like the pinions chewed in a little. About .005-.010. on half and up to .020 on the other. I plan on deburring the gears but I am wonder if I should do something to the case. Either have the wear welded up and machined smoot, or machined to make room for a hardened washer to mirror the other side?


I meant to attach these in my last post.


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Snowy Rivers

Well-known member
DO NOT WELD.....THE CASE IS IRON.....The small wear will not cause any issues in there.

Debur the teeth so they do not chew any more.

The inner compensator gears can move in and out a bit....really does not hurt anything.....Once the teeth are smoothed up they will stop chewing,

New gears were very sharp on the ends with AS machined teeth.....They act like cutters .... I rounded my teeth really well so hopefully it will stop the CHEWING....
There is no thrusting moment on these....so its not a big issue.....Main thing is to stop the thing from making metal particles that ruin bearings.
****Actually....there is some thrust....the drums have a really crappy thrust washer....if the drum can slop in and out a bunch it will shove the pinions some.....The thrust washers I used are designed to take thrust and handle it well****


These boxes are notorious for having crap in the oil.

The metal junk ruins bearings and then things grenade.... The thin shim washers used behind the drum and inside the compensator are not very study....they wear out...then break up and the junk goes through the R&P and the bearings....RUINS STUFF

The gear in the piccy has not been debured.....Just round all edges to eliminate the chewing.

The second piccy shows the same wear as you have...mine was a bit deeper....


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Snowy Rivers

Well-known member
More pics

PIC 13 shows the drum being machined.
PIC 18 shows the hardened washer sitting on the shoulder of the carrier with the drum in place and thrust washer installed inside....

The TH400 thrust washer sits well on the carrier hub (Relieve the center inside of the washer to fit the radfius)
The outer part of the drum hub needs to be cut back to allow the hard spacer to sit on the ledge when the unit is assembled and still allow the drum a bit of clearance... .010" or so. in and out....
The carrier hub was cut to allow two tangs on the washer to fit in and keep the washer from spinning.

Hard washer goes in next to the drum, then the carrier bearing shims and then the bearing.

The original shim pack should be fine...Just replace them back where they came from...The lock tab washers and nuts are standard items......
I made a wrench to tighten the nuts....The crew before me used a chisel ARRRRRRGH

Nobody had a wrench locally.
I turned up the ring to fit the nut, tapped 3 holes to allow Allen head bolts to screw inside to locate the wrench and one more Allen bolt to engage the slot in the nut..

Good club applied to the wrench handle will suffice to tighten the nuts....bend over the tabs on the washer....good to go...


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I will not be reusing all the shims. This one had a hard life and is ready to be replaced.
I saw your post on using transmission thrust washers and already acquired some. I will find a machine shop after the start of the year.


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Snowy Rivers

Well-known member
That washer looks to be brass ????
The ones that were in my box were steel....
The steel backed babbit and copper are loads better.... (Tranny washers)

Only draw back is that the case parts need to be machined to accept them.

The original design should have been done this way to make a far better set up...

Snowy Rivers

Well-known member
Mine was a complete rebuild.
Cat had been sitting for a long time....Box was about half full of water....A 5 alarm train wreck.
There were bearings that had failed....Thrust washers chewed up, bands were shot......

But the hard parts were still usable.


Did you have a failure or just servicing the oc12?
Just servicing. We recently acquired this Spryte and decide to go through the rear and make sure everything was good in there before we did anything else to the machine.

I feel like the diff is the only unique thing that we can't fab a replacement parts for.


That washer looks to be brass ????
The ones that were in my box were steel....
The steel backed babbit and copper are loads better.... (Tranny washers)

Only draw back is that the case parts need to be machined to accept them.

The original design should have been done this way to make a far better set up...
It is a steel shim, just looks off in that pic.

Snowy Rivers

Well-known member
The Diify is certainly something you can't just whip up stuff easily.......

Things like bearings, shims, bolts and such are easy.
From what I can see your diffy looks good.

Just a caution note


Now is a perfect time to fix things.

The bearings are all common numbered bearings.

I found all of mine on ebay at great prices...NEW OLD STOCK....

The big roller bearing at the gear end of the pinion shaft was costed out new at the industrial supply for $700 and change

I got the identical bearing NOS for $20 to my door

Shopping can save big $$$$$

These machines make lots of noise...You will likely not feel or hear a bad bearing in the diffy until it is way too late....and things start destroying stuff.

The ring and pinion are hard to find any more..... (Keep junk from leaving pieces that can go through the gears)