Derek's front 8" clam gets cryo treated 488 Nitro thick gears and an upgraded collar.
(67 BIG pics loading)
DEC 24 2017

This arrived from

Everything needed to regear the front and rear diffs in the FJC to 488.
The gear package from JT's basically consists of 4 boxes and 2 solid collars in baggies.
This kit works great as long as the original gears are the 373 ratio.
If the oem gears are 390 or 410 then a new carrier with the lower deck height would be needed....something ZUK probably has.

The above picture shows the carrier split that only the 8" clamshell has.
The oem 373 carrier on the right has a lower deck height....
the 11 tooth pinion is much larger in diameter so the ring gear
has to move farther away and that carrier allows it to happen.

The rear 8" on the left....front hi-pinion reverse cut ring/pinion on the right. They will be at Cryogenics International tomorrow.

Derek sent his diffs to me here.

Gears are back from cryo. Derek's front clam....488 gears....Nitro master kit....and the solid collar.

Remove the un-needed stuff.

This short axle stub comes out easy....

...from the other side.

Easy as butter.

Take the 10 bolts off that secure the lid.

Lid's off.

Remove the 10 flange style ring gear bolts. Good luck. Better have a really good socket and a really super impact wrench.

The thick Nitro 488 ring is now installed. Careful alignment initially to get the bolt holes to be in perfect alignment.

Lots of tapping with the lead filled plastic hammer to seat the tight ring gear.

85 ft/lb per the FSM with blue loctite.

New Koyo carrier bearings were really a tight fit but this hammer was up to the task. This end done.

Now onto the pinion end. Remove the flange.

Press the old 373 pinion out.

There is a special tool to pull the inner pinion race in place. As far as I can tell, it's not needed. <
I have no trouble using a stub hammer that fits in the limited space.

Fully 100% seated down and no damage.

The outer race is even easier.

Starting with a .0775" pinion shim on the new bearing.

Lots of gear oil on the pinion bearings and tighten the pinion nut only enough to get about 15 in/lb bearing preload.

A quick way to determine if the backlash is even the center carrier in and check for wiggle.
There was none here so can't run a paint test without backlash.

Using that just perfect scrap bearing part....

....Tap out the washer plate from the "bowl" and in my case here, went from a thin .069" to a .083".
And change out the washer plate on the lid side also.
Without a good washer plate selection, this can become a frustrating task.
Fortunately, I have a near full selection :)

Bolt it all back together.

So, with the lid bolted least some carrier bearing least some backlash values in the ball park....

I got lucky...only had to change the washer plate on each side only once to get a preload of about 5 in/lb and have a snug backlash of .005".
This is good enough for a paint test.

I already had painted 3 teeth ahead of time, and now, to offer resistance on the pinion flange while turning the sidegear with a cheater bar.

This gives me enough contact resistance to get an easy to read paint.
Here's the drive side and it's a bit too deep.....centered but deep.

The coast appears too deep also.

Drive....reverse painted.

Coast....reverse painted.

The comet tail on the pinion tooth is way too close to the face of the tooth(edge).



Let's try something thinner like .073"

Good time to increase the thickness of the washer plate in the bowl by .002" (from 083 to 085).
That will open up the backlash a little well as increase the preload a little more.

Repaint the teeth...

Repeat and turn the cheater bar back and forth 3 times. Remove the carrier and this is the result.
This is with a pinion depth shim of 073. Just a touch deeper than I want so will use 072 and that will be the winner.


Drive....reverse painted.

Coast...reverse painted.




More backlash checks....all looks in spect at this point which is almost the endpoint.

Now to finish up the pinion end, we just need to put the solid collar and seal in.

Took about 5 times to get the shimming right on the collar....typical.

With the shimming set it's just a matter of supporting the pinion in the hole...

...and tap the outer bearing in place and put the seal in also. This is a good seal...THO....Made in Japan. So we will use it.





The THO seal is next.

Recessed down .190"....evenly.

The oem flange was in excellent shape but #1500 sandpaper still made an appearance.

The high accuracy torque meter measured a smooth 10 in/lb.

FIPG for the lid.

45 ft/lb per the fsm with blue loctite.

The new drivers side seal is tapped in.

Looks good.