JP's 2017 Tundra Gets a Harrop A13791 with a Regear to REM and CRYO'd Nitro 529's
(73 BIG pics loading)
MAY 3 2020

JP's 2017 Tacoma


The 10.5" Nitro 529 rear gears were already "REM treated" locally and now they are at

REM makes them look almost like chrome and reduces the friction so no real break-in required.....
whereas Cryo reduces the Austenite content which has the affect of making the metal stronger.
Smoother....shinier ....stronger.

Items are layed out on the bench. The Harrop for the BIG 10.5" is a brand new item for the USA market.
It is not cheap.....retails at $2298.
We just happen to get serial number 001, too!

Disassembly begins on the 108 pound diff.

A paint test was performed on these "2-cut" face hobbed gears.

The 2 cut process is faster and cheaper than the 5-cut process but the 2-cut over time will see more wear
and pitting in the center of the tooth contact.

Bearing caps are removed.

Carrier bearing washer plates are tapped out.
These plates set backlash and carrier bearing preloads.

Part of the Nitro master crush sleeve is included because the factory already puts a solid collar in.


The 12 ring gear bolts are removed.

Pushing the pinion out...

Massive pinion flange.

Seal surface is in excellent shape.

The factory solid collar.

The factory pinion seal UH5186E



My seal remover made quick work of it.

The Nitro kit supplies a pinion seal but the genuine Toyota seal radiates quality.

Genuine vs Nitro




The massive outer pinion bearing comes out.

A simple washer cut in half to help push the old race out with no damage to the oil retainer under it.

Both races have been removed.

No damage to the oil retainer

New race going in and can use the old race to help tap it down with 360 degree support.


One good looking race tapped down 100% with an oil retainer under it.

The larger inner race takes more patience to get it to tap in straight.

100% seated.

Surfaces checked for burrs/ridges and all is good.

I didn't have the heart to scratch the REM surface :)

New ring gear was tapped on. The fit was still very tight.

Red loctite and 145 ft/lb on all 12 bolts.

The Harrop carrier is ready. Now to select a starter shim for the pinion....start with what was on there before.
No REM'ing of the bearing surfaces on the pinion....they obviously masked it off which was wise to do.

The new bearing was a nice, tight press fit as it should be.

Now to mount the pinion inside the differential carrier.

Only tighten the nut enough to develope about 15 inch/pounds of resistance.

Then mount the Harrop.....


First paint test using .0472" shows the drive side to be too deep.

Coast agrees with that.

Comet tail is flaring out to the outside and agrees.


Process is repeated and this time reducing the shim thickness to .041"

A slight adjustment to the washer plates.....


The softer brass hammer seems to do less damage to the washer plates.

Drive .041" looks better.

Coast is favoring the outside Heel.

Comet tail is more in the center....still says it may be too deep.


Disassemble again and reset with .039". This is looking good.

Depth look good but is close to the heel end. Sometimes there is very little to do to correct this.

I like the comet's about halfway between center and the root.

It's a keeper.

A little anti-seize under the bolt-head flanges keeps them from twisting the supplied bracket out of shape.

151 ft/lb per the FSM.

Backlash is recorded on every other tooth. Minimum backlash checking in at .007"

A final paint check.


Harrop coil test......measuring 3.8 ohms.

Live 12 volt test.

With 12 volts applied, the ring gear is turned slightly and the pins recess into the case(ramp affect)

Remove the 12 volts and the pins immediately snap in place.

The rubber grommet with the 2 wires is routed thru the carrier.

Hi Australia......Another 3 inches of wire sure would be nice......

Notes of the install.