Carlos Upgrades his 98 4Runner with a Rear Harrop and 488 Nitro Gears
(49 BIG pics loading)
March 16 2020

Carlos's 1998 4Runner

As received from Oklahoma....front 7.5" clamshell and an open 8" rear 3rd.

488 Nitro gear package from and a Harrop A9334 from
(rear 8" ring/pinion delayed a few days)

This link is for the rebuild of the rear diff which is in the fixture right now.

Product is unpacked and organized.

Diff has been cleaned using starting fluid and also a 10,000 rpm angle grinder with wire wheel attachment..

New large inner race is tapped in with 360 degree support.

The small outer race is tapped in with 360 degree support using an old race on top.

The oil retainer under the race will need to be flared up with another tool.

Flared just enough to clear the solid collar.

Now onto the Harrop and the Nitro ring gear.....surfaces checked with a file and no unusual burrs or high spots found.

91% alcohol cleans the ring gear nicely. It only took gentle taps to get the ring to seat....a slip fit.

73 ft/lb on pre-cleaned threads with red Loctite.

New Koyo races are tapped in....the fit was very tight which is desired.


This center carrier is now onto the pinion.

Taking a best guess and starting with a .079" shim

Mounting the pinion with no crush sleeve or solid collar. Those are not needed for just a paint test.

DRIVE side......favors toe end but the main concern it is way too deep.


COAST....looks actually kinda good....ever so slightly to the heel end.

Comet talks to me.....says that it is too deep....remove some shim.

Definitely remove some shim.....

Please remove some shim.(comet tail is favoring the outside)

DRIVE....reshimmed to .073" and a slight deep condition that I prefer...favors toe end.

COAST....can't go any more shallow.

Looking at the reverse painted DRIVE looks very nice.

COAST....reverse painted......good.

Comet tail is now where it should be. ....halfway between the center and the root.


Tail looks good right where it is.

The Nitro kit actually had a factory pinion seal in it. Probably the best insurance against a oil leak down the road.

NOK brand.



New Nitro 29 spline flange. I skipped a few steps but the solid collar is already in.

Crank on the pinion nut until I see 10 inch/pounds start torque.

The tabs are tweaked until I see about 2mm of freeplay....3 in this case.

Got a new Husky brand torque wrench(Home Depot)....old one lasted 10 years worth of gear installs....not bad.

Backlash is recorded from every other tooth.

Minimum is .006"


Now to check a few things on the Harrop. Verifying the magnetic coil resistance of 3.7 ohms.

Now the 12 volt functional test

12 volts applied...turn the pinion which turns the ring gear which forces the 3 pins to ramp up into the case.

Remove the 12 volts and the pins SNAP back out. Harrop works fine.

Done....except for a cosmetic coat of Black Satin Krylon paint.

Notes of the install.