Harrop elocker (8.4" 3rd) and Nitro 488 gears for Jose's '04 Tundra
(74 BIG pics loading)
SEPT 14 2017

2004 Tundra. Talk about a bird's eye view.

Beachin it.

Jose from California uses his Tundra for all the right purposes.....camping....

....more beaching......


Jose was needing more traction for some of the stuff he was running across and found out about a strong, selectable electric locker that was
available for the 8.4" diff. Yotalockers.com

A Nitro Gear 488 will be going in the front 7.5" clam but that's being saved for another link.

This box also arrived from Jose....most of the product had already purchased from Yukon before he found out about Nitro.

This link documents the rear 8.4" Harrop install.

Shown is the elocker, the Yukon master kit, the solid collar, and the Yukon 488.

A quick pre-check is made by applying 12 volts and verifying that the 3 pins start to cam into the case and they did.

Koyo bearings were supplied(preferred). Surprisingly, the kit also had the 12 flange style ring gear bolts.
The oem pinion seal was supplied by Jose. I have had some bad luck with generics in the past
and was happy to see that Jose had supplied the rear deal.

Good gears....manufactured in Korea.

Nice cuts all around....even in the root of the tooth shown here.

OEM rules....or even the Marlin seals work very nicely. BH4053G made by NOK.

Disassembly begins....the brace comes off first.

The 2 washer plates are removed and then the center carrier.

Pinion end next. The electric impact wizzed off the nut in 1 second.

Out with the old races and in with the new. Not seen but the factory .081" pinion depth plate was backed up with another .006" shim
for a total of .087" pinion shim depth.

An old race will knock it all the way down 100%.

Visible is the thick .081" factory washer plate and an almost hidden .006"shim.

The outer race is very easy to knock down.


The pinion shim is already located behind the inner race so just the new bearing gets pressed on here.

The 12 ton makes easy work of it.

The pinion is temporarily mounted and the nut tightened just enough have some preload.

A couple things need to be put on the Harrop elocker now.

Surface check.....no unusual ridges or burrs.

This particular Nitro was a very tight fit.....took forever just to get it started 1/8" down.

This made the other 1/2" go on like melted butter. All the time constantly checking the stop tabs to make sure nothing is binding or getting bent.

Securing the Harrop in the vice without scratching it.

The 12 ring gear bolts all get 92 ft/lbs and blue Loctite.

Carrier bearings next.

The factory washer plates went in too easy....

...so after a few tries, adding .003 to one side and adding .009" to the other made it fit tight enough with an adequate amount of backlash
to actually paint a legitimate pattern.

With the proper washer plates the backlash was checked.

The tabs were in the way of the brace....slight bending of each tab to clear the brace and to give the recommended ~2mm of stop tab play.

Drive looks nice. Depth is correct. Favoring of the toe.

Coast verifies that the depth is good. It's favoring the heel end.

Drive of the pinion tooth......comet tail is not tucked in hard to the tooth root.

Pretty much in the center which is perfect....actually that would mean "slight deep".

With pinion depth established, now I can turn attention to the grommet.

The .453" hole will be drilled about here....

.....right about here.

Solid collar to be installed now.

Doing the math, I'll start with .051".

The pinion is installed and the electric impact is used to cautiously tighten the pinion nut.

Pinion preload was way too high at about 35~40 inch/pounds.

From previous experience, for every .001" added to the shim will reduce the preload by about 8 in/lb.
Adding .004" should relax 32 of those inch/pounds.

NICE. Right on schedule. Just lucky again.

The master install kits generally come with generic pinion seals. A genuine Toyota seal is the best insurance against a leak.

Grease on the garter spring prevents it from popping off during the hammer hits.

All rubber surfaces are oiled up...

BAM!! The seal is tapped evenly down....fully flush.

Seal by NOK in Japan.

BH4053G for the 8.4" application.

#1500 fine grade wet/dry sandpaper is always used on the re-used flanges.



The pinion nut is cranked extra tight til a good solid 10 in/lb is noted....proof that the solid collars are not fully "solid".

DING!!! and the pinion nut will never loosen on its own.

I like to use RTV on the rubber grommet....acts as a lubricant and makes it possible to push the grommet thru the hole with less bad words.

A final tweak on the washer plates to open up the backlash to the .006" spec.
Without a good selection of factory plates, this is not possible.
And trying to add in .005" thin shims with the thick washer plates is unworkable.

With the bridge brace bolted in place and 83 ft/lb on all 4 bolts, now the final backlash readings can be recorded for every other tooth.

Pattern check. Only added about .0025" more backlash so the pattern really does not reflect any drastic change.


Testing the grey electromagnetic ring is easy.

Applying 12 volts as shown locks the camming ring to the grey electro ring....
Well, not really "locks" it but is attracted enough to allow the 3 pins to ride up the cam ring.

Disconnect the 12 volts and the cam ring snaps immediately into the resting position shown.(unlocked)

Double check....making sure there really is 83 ft/lb on the 4 bolts and there was.
Also, making sure there is about 2mm of stop tab play and there was actually closer to 3mm which is also just fine.

Engraving the ring with basic specs.

Measuring the resistance of the electromagnet coil and was almost exactly 4.0 ohms.
Ohm's Law says that even in a 16 volt system that the amps drawn thru a 4 ohm coil will be 16/4 = 4 amps.

My little test battery when loaded down was below 12 volts....and the current draw shown above (2.8 amps) reflects that.

A final snapshot of the notes.